Rinse-Off Products

Rinse-off products differ from leave-on products because they are only on the body transiently and are then washed away.

• Therefore, they are not generally used to deliver functional ingredients for absorption.

• They must deliver their function(s) rapidly.

• They might contain some minimal amount of ingredients designed to remain after rinsing.

• They can better tolerate the presence of ingredients that might cause irritation or allergies than a leave-on product.

• Mostly, rinse-off products for personal care are used as cleansers, so surfactants and solvents are key ingredients.

Cleaning – A Bit of History

• Ancient civilizations employed various methods for cleaning skin and hair using natural substances.

• Egyptian civilization: used soap-like materials made from animal fats, vegetable oils, and alkaline salts; oils and fragrances for hair.

• Mesopotamian civilization: used water, clay, and plant-based substances; olive and castor oils were used.

• Greek and Roman civilization: used water, oils, and other botanicals; olive oil scented with herbs or flowers; bathhouses were very popular.

Key Roles of Surfactants

• Emulsifiers

• Detergents

• Wetting agents

• Solubilizing agents

• Dispersing agents

• Suspending agents

• Foaming and antifoaming agents

Detergency

• If detergents clean mainly by reduction of surface tension, then why doesn't everyone just use SLES (sodium laureth sulphate)?

• SLES produces low surface tension, is safe, and is cheap.

• However, low surface tension alone is not sufficient for effective cleaning.

Surface Tension vs Interfacial Tension

• For general dirt (soil), water needs to get in to reduce forces between molecules.

• Surface tension matters for wetting the surface – low surface tension allows water to reach dirt.

• Once water reaches dirt, removal depends on interfacial tension (dirt-water).

• When optimized, low interfacial tension allows oil to detach from the surface and break into droplets.

• A monolayer of water reduces van der Waals attraction by orders of magnitude (1/r⁶ dependency).

• Low interfacial tension and curvature are needed more than just low surface tension.

Detergency Mechanisms

• Solubilization (micellar): oil molecules partition into micelles; works very well for small amounts of oil; true for most hand washing.

• But if you coat your hand in olive oil and wash with a foamed hand cleanser, it needs an awful lot of soap.

• Emulsification: oil forms droplets, coated with surfactant, and stabilized against coalescence.

• Shampoo and dishwashing are emulsification-dominated.

Achieving Good Detergency

• You want to achieve low interfacial tension at the wash temperature.

• HLD = 0 is good for solubilization but poor for emulsion stability.

• Droplets removed from surfaces might easily contact and spread on another.

• Therefore, an HLD slightly below zero is best.

• Most commercial detergents contain polymeric surfactants – great solubilizers but too slow when used alone.

• Use conventional small molecules to get oil off the surface, and polymeric surfactants to prevent re-deposition.

• A system of around 5-15% anionics and 5-15% non-ionics tends to work well.

• Polymers used for steric stabilization; anionic cellulosics stick to cellulose fibers and repel anionic dirt particles; PET-PEO di-block polymers stick to PET fibers; polyacrylics are the workhorse anionics for sequestration of Ca ions, charge stabilization, and avoidance of re-deposition.

Consumer Perspective and Technical Quality

Consumer perspective:

• Neutral or pleasant odor and color.

• Easy to rub on with appropriate foaming property.

• Easy to spread.

• Pleasant feeling during application.

• Non-oily/non-greasy feeling.

• Leaves no residue.

• Moisturizes the skin while cleaning.

• Non-comedogenic.

• Well tolerated and non-allergenic.

• Hand sanitizers: do not dry the skin, but kill bacteria and viruses.

Technical quality:

• Long-term stability.

• Smooth texture.

• No microbiological contamination and growth.

• Appropriate rheological properties.

• Appropriate foaming activity.

• Appropriate performance.

• Appropriate pH.

• Dermatological safety/reduced irritancy.

Choosing Detergents in Wash Products

• (Title slide – limited content)

Additional Formulation Notes

• Colorants may contribute to marketing appeal; both natural and synthetic colorants can be used; titanium dioxide or glycol stearate used as opacifiers.

• Fragrances mask odor of raw ingredients but may be highly irritative, especially for sensitive skin.

• Preservatives provide protection against microbiological contamination (parabens, phenoxyethanol, benzoates).

• pH buffers may be used: alkaline solutions for saponification (potassium hydroxide, sodium hydroxide, ammonium hydroxide); citric acid and lactic acid shift pH to acidic range (closer to natural skin pH, less irritant); pH buffers like triethanolamine may be needed to thicken formulation via neutralizing thickeners.

Antibacterial Agents and Other Ingredients

• Antibacterial agents are widely used; may be beneficial for acne, superficial skin infections (folliculitis), and infection control.

• Most commonly used compound is triclosan (safety/efficacy currently being investigated by FDA).

• Additional examples: benzoyl peroxide, lactic acid (soaps with higher lactic acid have acidic pH, thought to be antibacterial).

• Absorbents mainly used in facial masks to absorb sebum (zinc oxide, titanium dioxide, kaolin, calamine, clay, natural mud).

• Astringents are major ingredients in facial toners; tighten pores and refresh skin (alcohol, witch hazel).

• Certain soaps contain vitamins and exotic natural ingredients (derived from fruits, other plants).

Solvent Cleaners

• Solvents (EtOH, IPA, etc.) are great for industrial cleaning but perceived as "bad" by consumers.

• Subject to ever-more-restrictive rules on volatile organic content (VOC).

• Purely aqueous cleaning with modest surfactant can be fine for many soils but useless when soil requires solvency.

• A compromise is to deliver solvent within an aqueous environment – perceived as user-friendly and environmentally benign.

• If solvent is fully water-soluble, unlikely to be a good solvent for water-insoluble oil.

• An effective solution for water-insoluble solvents is to deliver them as a microemulsion.

Why a Microemulsion?

• If drops are relatively large, the amount of surfactant required to cover and stabilize the emulsion is modest (advantage).

• However, such emulsions are generally not successful because the emulsion must be stable for practical use – the surfactant shell around the solvent drop provides a barrier to effective cleaning.

• The more stable the emulsion (so it can be shipped and used conveniently), the less effective it is as a cleaner.

• Therefore, a microemulsion with smaller droplet size can be more effective, although it takes higher amounts of surfactant.

• Applications: industrial adhesive removal, degreasing and tar removal.

Foams

• When a group of spherical bubbles meet so that most water has disappeared ("dry" foam), the most energy-efficient form of packing involves polyhedral faces.

• Making foams is easy – keeping them needs a surfactant.

• Key properties: elasticity, disjoining pressure, resistance to ripening, resistance to draining, resistance to defects.

• Foam bubbles are made from film walls, linked by Plateau borders which meet at nodes.

Anti-Foams

• Antifoams can be pure oils, pure hydrophobic particles, or blends.

• The problem is to make them with small droplet size – using a surfactant.

• Silicones tend to be most successful at 0.2% surfactant because they are harder to emulsify than oils.

• Another class of antifoams destroy the surfactant itself rather than the foam.

• Hard water when surfactants are fatty acid salts (e.g., sodium stearate) – calcium ions cause stearate to become insoluble and foam disappears.

• A small amount of cationic surfactant can rapidly destroy an anionic surfactant foam.

• Adding a lot of salt to a foam with large electrostatic disjoining pressure can reduce the disjoining pressure, thin the foam, and make it more susceptible to collapse.

• Added to carpet extractors and scrubbers to protect vacuum motors from liquid intake.

Surfactant Types and Properties

Non-ionic:

• Low stable foam, supports other surfactants, emulsifiers, solubilizers.

• Examples: glycerol-based (emulsifiers), sorbitol-based (solubilizers), e.g., sorbitan isostearate, PEG-castor oil, Cocamide DEA, Lauramide MEA.

Anionic (negative charge):

• Wetting agents, good detergency, cleaning, high coarse foam.

• Examples: alkyl and alkyl ethoxy sulfates, alkyl aryl sulfonates, alpha olefin sulfonates, e.g., sodium lauryl ether sulfate, ammonium laureth sulfate, sodium lauryl sarcosinate.

Anionic soaps:

• Hard soap = sodium salts of fatty acids (sodium cocoate, sodium palmate).

• Soft soap = potassium salts of fatty acids (potassium laurate, potassium palmate).

Cationic (positive charge):

• Conditioning agents, antistatic, very low foaming; cannot mix with anionics.

• Examples: quaternary ammonium salts (Quaternium-80, Behentrimonium chloride, silicone quaternium).

Amphoteric or Zwitterionic (dual charge):

• Mild-to-fine foaming, used in 2-in-1 shampoo.

• Contain dual functional groups: anionic in alkali, nonionic at neutral pH, or cationic in acid.

• Example: Cocoamido propyl betaine.

Surfactant Comparison Table

Good Cleansing Formulation Principles

• Good cleansing – choosing the right surfactant or combination based on expectations.

• Good viscosity – micellar arrangement/behavior, co-surfactants, thickeners, electrolytes, compatibility of ingredients and processes.

• Foaming – based on selection of surfactants depending on the brief.

• No precipitates/separation – all ingredients well solubilized, no chelation.

• Reduced irritancy – reduced harshness, superfatting agents, pH is skin compatible.

Surfactant Irritancy Mechanisms and Reduction

Mechanisms of irritancy:

1. Surfactants bind to skin proteins and denature them.

2. Bind to lipid matrix, making skin permeable.

3. Disrupt natural moisturizing factor (NMF).

4. Stimulate anti-inflammatory response by interacting with epidermal cells.

5. Stimulate oxidative response.

Methods to reduce irritancy:

1. Use only mild surfactants (non-ionics/ethoxylated anionics).

2. Blend with amphoterics (betaines).

3. Polymer/hydrolyzed protein additives.

4. Refatting agents/refatteners (fatty acid esters, fatty alcohols, various oils).

5. Antioxidants.

Fragrance Use in Rinse-Off Products (EU Regulations)

• All ingredients added as fragrances must comply with IFRA's code of conduct.

• Fragrances may be classified as H412 or H413.

• Products recommended/advertised for babies may not contain fragrances.

• Nitro musk and polycyclic musk compounds are prohibited.

• The following fragrances are permitted only up to 0.01%:

  • Benzyl alcohol, Amyl cinnamal, Cinnamyl alcohol, Citral, Eugenol, Hydroxycitronellal, Isoeugenol, Amylcinnamyl alcohol, Benzyl salicylate, Cinnamal, Coumarin, Geraniol, Hydroxyisohexyl 3-cyclohexene carboxaldehyde, Anise alcohol, Benzyl cinnamate, Farnesol, Butylphenyl methylpropional, Linalool, Benzyl benzoate, Citronellol, Hexyl cinnamal, Limonene, Methyl-2-octynoate, Alpha-isomethyl ionone, Evernia prunastri extract, Evernia furfuracea extract.

Resources and Further Reading

• Baki, G., & Alexander, K. S. (2015). Introduction to cosmetic formulation and technology.

• Carli, B. (2016). Cosmetic Formulations: An Advanced Guide.

• Barel, A. O., Paye, M., & Maibach, H. I. (2014). Handbook of cosmetic science and technology (4th ed.).

• Darvin, M., & Lademann, J. (2007). Dermatologic, Cosmeceutic, and Cosmetic Development.

• Tadros, T. F. (2016 & 2018). Formulation Science and Technology & Formulations: In Cosmetic and Personal Care.

• Barton, S. et al. (Eds.). (2020). Discovering Cosmetic Science. Royal Society of Chemistry.

Anionic Surfactant – Sodium Laureth Sulfate (SLES)

• INCI: Sodium Laureth Sulfate (Sodium Lauryl Ether Sulfate) – NOT SLS.

• Very effective surfactant and foaming agent, derived from palm oil or coconut oil.

• Low cost.

• Has mild irritancy to the skin (whereas SLS is a known irritant).

• Typically has pH of around 7–9 at 2% in water.

Anionic Surfactant – Sodium Coco Sulfate

• INCI: Sodium Coco Sulfate; minimum 90% active content.

• Natural, high foaming, anionic surfactant suitable for Ecocert formulas where thickness is required.

• Can be irritating to the skin – addition of mildness-improving ingredients recommended.

• Works best in pH range between 6 and 12; may require a chelating agent.

Anionic Surfactant – Sodium Cocoyl Isethionate (SCI)

• INCI: Sodium Cocoyl Isethionate (powder or granules).

• Very mild surfactant designed to work effectively in hard water.

• Derived from coconut fatty acids; fully biodegradable.

• Gentle enough for baby products and personal cleansers for sensitive areas (e.g., eye-makeup removers).

• Leaves a silky skin feel whilst exhibiting excellent lathering properties.

• Usage: 3–40% in heated phase of surfactant formulations.

• Solubility: soluble in water.

• pH (1% in water): 4.5–7.5.

Anionic Surfactant – Sodium Lauryl Sulfoacetate (SLSA)

• INCI: Sodium Lauryl Sulfoacetate; minimum 65% active content.

• Mild surfactant perfect for powdered bubble baths, shampoos, cleansing creams, and bath bombs.

• Naturally derived from palm and coconut oils.

• Offers rich lather without irritation potential of some other foam-building surfactants.

• Due to large molecular size, will not penetrate skin or mucous membranes.

• Non-irritating to skin up to 70%; non-irritating to eyes up to 3%.

• Usage: 0.5–3% in skin care applications, baby products, pet products; 2.0–10% in body washes, soaks, shampoos.

Amphoteric Surfactant – Cocamidopropyl Betaine

• 29–31% active content.

• Mild co-surfactant compatible with anionic, non-ionic, and cationic surfactants; also useful as primary surfactant.

• Effective cleanser, foam booster, and increases viscosity of finished product.

• Excellent conditioning and antistatic agent.

• Common in shampoos, conditioners, bubble baths, cleansing lotions, hand soaps.

• Palm-free, derived from coconut oil.

• Solubility: water soluble.

• Usage: 4–10%.

• pH: 4–12.

Non-Ionic Surfactants – Coco and Decyl Glucoside

Coco Glucoside:

• 51–53% active content.

• Non-ionic surfactant used as foaming, cleansing, conditioning, and thickening agent.

• Derived from coconut and/or palm oil and corn sugars; completely biodegradable; gentle on all skin and hair types.

• Works best in pH between 4 and 12.

Decyl Glucoside:

• 51–55% active content.

• Extremely mild and gentle non-ionic surfactant naturally derived from sugar.

• Recommended for sensitive skin, facial wash products, shampoo, and body wash.

• Generates exceptional fine and stable foam.

• Readily biodegradable, low toxicity, extremely mild, performs well in hard water.

• Non-irritating even at high concentrations with extended contact (24 hours).

• Works best in pH between 4 and 12.

Non-Ionic Surfactant – Lauryl Glucoside

• 50–53% active content.

• Natural surfactant made from coconut oil and/or palm oil and sugar.

• Very gentle – popular in products for sensitive skin and baby products.

• Part of the alkyl glycoside family (APGs).

• Made from renewable, sustainable raw materials; readily biodegradable.

• Works best in pH between 4 and 12.

Superfatting Additive – Lamesoft PO 65

• INCI: Coco Glucoside and Glyceryl Oleate (superfatting).

• Naturally derived from coconut and sunflower oil.

• High-performance additive that supports moisturization claims in surfactant systems.

• Softens and conditions skin by depositing glyceryl oleate on its surface.

• Lipid layer enhancer for surfactant-based cleansers.

• Improves mildness of formulation; enhances viscosity in sulfate-free systems.

• Cold processable – saves time and energy.

• Can be used in clear, opacified, and pearlized formulations.

• 100% naturally derived.

• Usage: between 1–5%:

  • 1%: proven lipid layer enhancement in 'light' formulas.

  • 3%: perceivable skin softness and smoothness.

  • 5%: 24-hour moisturization.

Cationic Surfactant – BTMS-50

• INCI: Behentrimonium Methosulfate (&) Cetyl Alcohol (&) Butylene Glycol.

• Natural emulsifying wax; can emulsify creams, lotions, and scrubs leaving soft silky feeling.

• Most used to make hair conditioners.

• Cationic (positively charged) – conditioning agent giving excellent detangling, antistatic, and softening properties in leave-on and rinse-off hair care.

• Extremely popular in solid bar recipes.

• Contains 50% active content (BTMS-25 has 25%, BTMS-80 has 80%, palm-free).

• Comes as easy-to-use flakes.

• Potential applications: conditioners, shampoos, solid bars, creams, lotions, body butters, balms.

• Usage: usually up to 15%.

Hair Care Formulations (Conditioners and Styling)

New Hair Style and Maintenance

New hair style:

• Increase or decrease volume, straightness, curliness.

• In straight hair, volume and alignment are inversely related; however, some polymers can increase fiber diameter.

• In textured hair, volume is dependent on hair curvature.

• Enhancing lubricity and/or glueing hair fibers in a new position.

Maintaining a hair style:

• Prevent the uptake of moisture from the atmosphere.

Hair Styling

• Polymers – used in styling gels, foams, mousses, lotions, creams, and finishing sprays.

• Type, combination, and concentration of polymers define level of hold and stickiness.

• Polymer films may be brittle and tough or plastic and soft.

• Plasticizers (polyols, surfactants) can adjust product finish.

• The stronger the hold, the more water resistance matters.

• Volatile organic solvents may be required.

• Oils and waxes – provide lubrication, smoothness, and water impermeability, particularly useful in textured hair.

• Powders – provide matte appearance and enhance grip by increasing friction.

Conditioners: Purpose and Overview

• Sebum is a natural and effective 'conditioner', but constant removal by washing and rubbing means consumers need extrinsic compounds.

• Conditioners are used for:

  • Increasing smoothness.

  • Easier wet and dry combing.

  • Reducing static electricity.

  • Adjusting volume and improving texture.

• Incorporating conditioning agents into shampoo formulations can significantly enhance performance.

Rinse-Off vs Leave-On Conditioners

• Rinse-off conditioners: deliver intensive care through concentrated formulas for short-term contact; rich texture penetrates deeply during brief application; washes away cleanly without residue.

• Leave-on formulations: feature lighter molecular weights and specialized dispersing agents that prevent buildup; provide continuous protection against environmental stressors while maintaining optimal moisture levels.

• Choice depends on hair porosity and structure:

  • Fine hair benefits from lightweight leave-on sprays.

  • Thick or coarse textures may require both (rinse-off for deep nourishment, leave-on for ongoing care).

• For straight, fine strands: light plant-derived esters with hydrolyzed proteins create effective products that don't weigh hair down.

• Wavy and curly patterns: balanced formulas with panthenol and botanical extracts (aloe vera) enhance natural curl definition while maintaining moisture balance.

• Tightly coiled/textured hair: rich butters combined with hyaluronic acid provide deep nourishment.

Common Conditioning Agents

1. Cationic polymers (e.g., polyquaterniums): positively charged, adhere to negatively charged hair shaft, offer detangling, static control, and improved combability without interacting negatively with anionic surfactants.

2. Silicones: impart smoothness, shine, and manageability by forming thin layer around hair shaft, reducing friction and providing protection; most widely used is dimethicone.

3. Fatty alcohols (cetyl, stearyl, cetearyl alcohol): improve texture and spreadability while providing conditioning and emollient properties.

4. Natural oils and butters (argan oil, coconut oil, shea butter, jojoba oil): help replenish lost lipids, nourish, hydrate, and improve overall hair health.

Cationic Surfactants

• Carry positive charges in aqueous medium, easily adsorbing to negatively charged wet hair.

• Mainly used in rinse-off formats.

• Quaternary ammonium compounds (quats) often have preservation-boosting properties.

• Potentially the most irritant surfactants.

• Form primary emulsifier for the conditioner, creating an emulsion.

• Quats represent the vast majority of this class.

• Concentration of these ingredients (typically 3–6%) significantly impacts conditioning level.

• Higher concentrations provide more intense conditioning but can lead to build-up or heavier feel, especially on fine hair.

Quaternary Ammonium Compounds

• (Title slide – limited content)

Polyquaterniums

• Cationic polymers that adsorb to wet hair via electrostatic attraction.

• Molecular weight and charge density define properties:

  • High molecular weight increases product viscosity.

  • Low molecular weight increases hair adsorption.

  • Higher charge density increases hair adsorption.

• Some modern versions ("ester quats") incorporate ester linkages, improving biodegradability and gentleness compared to traditional quats.

Fatty Alcohols and Rheology Modifiers

• Fatty alcohols work synergistically with cationic surfactants to form stable lamellar gel network (key for emulsion stability and viscosity).

• Contribute to emulsion structure, provide body, enhance rich creamy texture, add conditioning feel and lubrication.

• Ratio of fatty alcohols to cationic surfactants is critical for optimal viscosity and stability.

• Typically, a ratio of 1:1 or slightly higher fatty alcohol yields desirable creamy texture.

• Rheology modifiers (natural gums, synthetic polymers) create optimal viscosity profiles while ensuring proper ingredient distribution.

Sensory Emollients – Oils and Silicones

• Sebum and 18-MEA make hair partially hydrophobic, especially if undamaged.

• Hydrophobic conditioners are attracted to hydrophobic parts of hair; provide lubrication, enhance shine, contribute to softness, help replenish lost lipids.

• This category includes:

  • Various plant-derived oils (argan, jojoba, coconut).

  • Natural butters (shea, mango).

  • Synthetic or naturally-derived esters.

  • Silicones: dimethicone, dimethiconol, amodimethicone (additional electrostatic attraction in acidic conditions).

• Reactive silicones can form long-lasting films after deposition.

• Selective deposition on damaged hair; better conditioning efficiency; lower buildup than dimethicone; common in premium conditioners.

• Total emollient phase: ~5%–25%, adjusting based on desired richness.

Key Mechanisms of Action and Role of pH

3 deposition mechanisms:

1. Primary adsorption: cationic surfactants create positive charge density that bonds with damaged keratin sites; forms stable layers of amino acids and conditioning agents.

2. Secondary mechanisms: oil phase components and specialized polymers; when properly emulsified, create structured lamellar networks that deposit during rinse phase; cationic guar gum enhances this process.

3. Quaternary deposition: dilution-triggered release of conditioning agents; as water dilutes formulation, previously solubilized ingredients precipitate onto fiber surface.

Role of pH:

• Finished pH of conditioner is critical for hair health.

• Acidic pH (typically 3.5–5.0) helps close hair cuticles, leading to smoother, shinier hair and reducing frizz.

• Cooling rates between 0.5–2°C per minute optimize development of lamellar structures.

Hair Conditioner Formulations – Manufacturing

Manufacturing process:

1. Add 90% of water and cetrimonium chloride to main vessel; heat to 70–75°C.

2. Melt cetearyl alcohol in jacketed side vessel; heat to 70–75°C.

3. When both phases at 70–75°C, add oil phase to water phase with homogenization to form emulsion.

4. When emulsion has formed, commence cooling to 40°C with paddle stirring only.

5. Dissolve preservative in portion of reserved water; add to main vessel with continuous mixing.

6. Add color to main vessel; continue cooling.

7. Add fragrance; mix until homogeneous.

8. Adjust pH with citric acid dissolved in water to pH 3.0–5.0.

9. Cool to 35°C.

Typical Hair Conditioner Formulation (% w/w):

• Cetrimonium chloride (CTAC) 30% active: 3.00%

• Cetearyl alcohol: 2.80%

• Perfume: q.s.

• Preservative: q.s.

• Citric acid: pH 3.0–5.0

• Color: q.s.

• Water (deionized): to 100.00%

Testing Conditioners – Combing, Static, and Gloss

• Test swatches of hair can be assessed in-vitro to determine effect on combing.

• A comb with a spring gauge measures resistance to combing; method can be used in-vivo without modification.

• Effect on static electrification of dry hair can be assessed using a charge locator (valve voltmeter with probe connected to grid).

• Greater bias of grid = larger charges affecting probe; measurements can be in-vitro or in-vivo.

• Gloss/lustre can be quantified by scientific instrument in-vitro; in-vivo measurements are more difficult as perception of gloss accounts for both reflected and scattered light.

Stability Testing

Why Test Stability?

• Stability: the ability of a cosmetic product to resist change of its initial properties over time under reasonably foreseeable or stated conditions of storage and use.

• Looks at how product quality varies with time under influence of intrinsic and extrinsic factors.

• Stability studies test parameters susceptible to change that influence quality, safety, and efficacy.

• It is a company's responsibility to ensure the product put on the market is safe when used as directed.

Information Gained from Stability Testing

• Predicted product shelf-life.

• Recommended storage conditions.

• Length of time product is expected to maintain quality.

Types of stability considered:

• Physical: original physical characteristics should not change (viscosity, look, smell).

• Chemical: ingredient chemistry and composition should not be altered; remain within limits if applicable.

• Microbiological: preservative systems, GMP, and appropriate packaging should ensure microbial growth limits are not exceeded.

• Functional: product attributes should not change, in line with product claims.

• Safety: mandatory by regulation.

Intrinsic and Extrinsic Factors

Intrinsic factors:

• Physical stability: solubility, precipitation, polarity, phase separation, cohesion.

• Chemical stability: pH, chemical reactions, adsorption.

Extrinsic factors:

• Time, temperature, radiation, oxygen, humidity, packaging material, microbial growth, vibration.

Shelf-Life

• Shelf-life: time period during which product is expected to remain within approved specifications when stored in conditions defined on the label.

• Release specifications (Quality Control): acceptance criteria defining product at time of release to market.

• Shelf-life specifications (Product Development and Stability Testing): acceptance criteria product should meet throughout its shelf-life.

• Shelf-life for commercial personal care product is normally 2–3 years and ~6 months once open.

Required label information:

• Name and function of product.

• Name/address of responsible person.

• Nominal value.

• Expiration date ("Best before" or preceded by symbol).

• If expiration date >30 months, may not be reported; PAO (Period After Opening) must be reported with small jar symbol followed by period.

• Particular cautions for use.

• Batch number.

• Ingredient list.

Period After Opening (PAO)

• Defines the authorized period a product may be used after opening without harm to consumer.

• PAO must be indicated for products with shelf-life over 30 months.

• Products with shelf-life of 30 months or less must state an expiry date.

PAO not required for:

• Single-use formats.

• Pressurized-container aerosols.

• Products where microbial growth is virtually impossible (e.g., high concentration of ethanol).

No formal way to define PAO – depends on:

• Stability testing data.

• Type of packaging.

• How consumer interacts with product.

• How product is often stored.

• Where product is applied.

New Zealand Regulations for Stability

• Regulations fall under EPA and Ministry of Health.

• No general legal requirement for formal GMP certification (unlike EU's ISO 22716).

• General guidelines include adherence to GMP, ingredient safety, stability testing, and labeling requirements.

• In practice, many NZ brands voluntarily follow cosmetic GMP principles; retailers/distributors may require it; insurers may expect evidence of quality systems; export markets (EU, ASEAN, GCC) effectively force GMP compliance.

Early Signs of Instability

• Changes in color, texture, fragrance, and separation of ingredients.

Signs of Instability – Emulsion and Contamination

• Emulsion breakdown: if product recalled because emulsion has broken down, investigate distribution and whether supply chain routes face extreme temperatures/fluctuations during transport.

• Bacterial contamination: don't immediately blame preservatives; production engineers should examine assembly line for contamination sources.

• Preservative role: preservatives prevent contamination from consumer fingers; not meant to cover all microorganisms but target common ones (fungus, yeast, bacteria); test preservatives for ability to stick to jar walls – if they stick, they might not reach bulk of product.

Example – Vitamin C Serum Oxidation

• Dermalure oxidation chart shows color progression from clear/light to dark amber.

• Fully oxidized serum turns dark amber.

• Do not use once color turns to dark amber.

• Both serums are safe and effective until fully oxidized.

Formal Stability Testing

• Stability should be tested in new products and whenever any product variable changes:

  • Packaging.

  • Ingredient supplier.

  • Ingredient trade name.

  • Formulation composition.

  • Manufacturing method.

  • Production equipment.

• Product should be tested in final container-closure system (formulation-packaging compatibility).

• Product must be sealed as it would be in market; all primary packing components included (container, lids, pumps, labels); ideally secondary packaging also included.

Types of Stability Testing

• Long-term stability: should last for at least the expected product shelf-life or 5 years.

• Accelerated stability: helps provide shelf-life information in short time by accelerating "normal" storage conditions.

• Stress stability: helps formulator quickly assess how robust the product is during formulation development.

Example testing schedule:

• Initial time point.

• After 1 month.

• After 3 months, then every 3 months in 1st year.

• Every 6 months in 2nd year.

• Annually throughout proposed shelf-life period.

• Usually stopped at 5 years.

Accelerated stability uses adverse conditions to predict/indicate likely stability – no guarantee but good indication.

Stability Testing by Product Type

• Emulsions: all stability testing.

• Oils/balms/sticks: all except microbial and mechanical.

• Surfactants: all stability testing.

• Powders: all except cold challenge, freeze/thaw, climate chamber, but include microbial.

Formal stability studies: a new product is opened for the 1st time at each testing time.

Long-Term Stability Testing – Climatic Zones

• (Title slide – diagram/content limited)

Long-Term Stability Testing – Climatic Zone Definitions

Setting storage temperatures on packaging:

• EU/UK: 20°C

• Australia: 25°C

• Tropical climates: 30°C

Accelerated Stability Testing

• Done in a climate chamber.

• Typical testing conditions: 40°C ± 2°C (ideally at 2–3 temperature points), 65% RH ± 5% RH.

Example schedule:

• Initial time point.

• After 1 month.

• After 3 months.

• After 6 months.

Approximately, 10°C rise in temperature doubles the rate of reactions.

• The greater the "acceleration", the more likely product changes occur that would never occur in market conditions.

• Fragile products may require lower temperatures, therefore longer periods of testing.

• Excessive temperatures may no longer accelerate "normal" conditions.

• Indicator of stability, but not of instability.

Elevated Humidity Tests

• Although products may be affected by humidity, it is the role of the container closure system to protect them.

• Formulation instability due to humidity indicates inadequate protection from packaging.

• Elevated humidity tests assess:

  • Effect of humidity on packaging.

  • Barrier properties of container-closure system.

• Elevated relative humidity is a test of the pack, not a direct test of the product.

Quantifying Stability Results

• Many product specifications can be quantified; acceptable results must be within specification range (e.g., pH: 5.0–6.0; Methylparaben assay 95–105%).

• When specifications are subjective, a scale of change from baseline is helpful:

  • 0: No observable change/Barely discernible change.

  • 1: Slight change.

  • 2: Distinct change.

  • 3: Marked change.

  • 4: Very marked change.

• Examples: organoleptic properties, compact powder resilience (drop test).

Stress Stability Testing

• A formulator's tool; no formal requirement – depends on company's product development strategy.

• Informative to the formulator, but do not indicate shelf-life.

• Focused on specific product parameters, not holistic stability.

• Indicative of intrinsic stability of formulation – not used to assess final product's stability.

Types of stress tests:

• Mechanical tests (vibration, accelerated gravity).

• Cycling tests (temperature and humidity).

• Freeze/thaw.

• High temperatures.

• Microbial challenge.

• Xenon weathering (light).

Cycling Tests

• Involve variation of temperature and humidity over days or weeks.

• Can be more stressful than constant temperature/humidity because acceleration and deceleration of particles under Brownian motion creates chaos.

• Effective test for products being sold in different climates.

• Example: 24-hour cycles of 25°C and 45°C, or 5°C to 25°C.

Freeze/Thaw Tests

• Subject products to extreme freezing followed by thawing at room temperature in 24-hour cycles.

• Cycles include temperatures from -18°C to -30°C, followed by room temperature (25°C/30°C).

• Ideal for assessing likelihood of cleansing products crystallizing or clouding and emulsions separating.

• Conducted on solutions, emulsions (creams/lotions), liquids, and semi-solid products.

Results:

• 5 cycles typically represent stability over 24 months.

• 6 cycles usually indicate stability over 30 months.

Other Stress Tests

• Vibrations: mimics transportation; shows physical stability of disperse systems and powders; tests over range of frequencies and amplitudes.

• Accelerated gravity: centrifuge at 3000–4000 rpm (10–15 mins); tests accelerated phase separation in disperse systems.

• High temperatures: 60–80°C; tests chemical stability.

• Xenon weathering (light test): ~24h illumination at 765 W/m² (mimics sunlight); results may not be truly indicative.

• Light cabinet: usually twelve 40W fluorescent lights, product kept at 30cm from light sources; relevant for products containing dyes (especially natural dyes); products in clear/translucent packaging should be tested.

Ideal for short time frames and/or to provide short-term indication of stability before running longer, more extensive tests.

Microbiological Analysis – Routine and Screening

• Originating from production, filling, and consumer use, microbial contamination is a continuous concern.

Routine Microbiological Analysis:

• Each batch must undergo regular testing before market release to detect potential pathogens (Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans).

• Goal: ensure pathogens are not detectable in 0.1 g or 0.1 ml of product.

Screening Tests:

• Quick and semi-quantitative kits (dip-slides, plate counts) available for easy assessment of contamination levels.

• Provide rapid results; can be used by personnel without extensive microbiological training.

Quantitative Tests:

• Professional labs conduct precise bacterial, mold, and yeast counts.

• Require sophisticated methods (direct colony counts, enrichment culturing).

Microbial Challenge – Ph. Eur. Method

Test organisms:

• Bacteria: Pseudomonas aeruginosa, Staphylococcus aureus.

• Fungi: Candida albicans, Aspergillus niger.

Acceptance Criteria (Log Reduction Values in CFU):

NI = no increase from previous contact time.

Microbial Challenge – ISO 11930:2019

Test organisms:

• Bacteria: Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli.

• Fungi: Candida albicans, Aspergillus brasiliensis.

Criteria A (product is protected):

• Bacteria at T7: ≥3, at T14: ≥3 and NI, at T28: ≥3 and NI.

• C. albicans at T14: ≥1, at T28: ≥1 and NI.

• A. brasiliensis at T14: ≥0, at T28: ≥1 and NI.

Criteria B (product does not satisfy all requirements but risk is acceptable):

• Bacteria at T14: ≥3, at T28: ≥3 and NI.

• C. albicans at T14: ≥1, at T28: ≥1 and NI.

• A. brasiliensis at T14: ≥0, at T28: ≥0 and NI.

Acceptable range of deviation: 0.5 log.

New Zealand Regulations – Additional Info

• Good Manufacturing Practices (GMP): manufacturers expected to adhere to GMP guidelines ensuring consistent production and quality standards; includes stability testing protocols.

• Ingredient Safety: ingredients must comply with EPA and other relevant authority regulations.

• Stability Testing: manufacturers usually required to conduct stability testing to ensure safety, efficacy, and shelf-life.

• Labeling Requirements: accurate and informative labeling including shelf-life, storage conditions, and precautions for use.

• NZ doesn't have specific group standards for stability testing of personal care products and cosmetics.

• However, NZ often aligns with international regulations (ISO, FDA, EU Cosmetic Regulation (EC) No 1223/2009).

• Relevant resources: EPA (Buying, using and storing cosmetics and toiletries); Regulation (EC) No 1223/2009; Recall websites (Product Safety New Zealand, SGS United Kingdom).

Māori Perspective of Product Formulation

Māori Perspectives on Product Formulation

• (Title slide – presenter and course information)

Antony Nihoniho (Ngāi Tahu / Ngāti Porou / Ngāti Pākehā)

• Contact details and affiliations.

• Ancestral connections: Ngāti Porou (Te Tai Rāwhiti), Ngāi Tahu (Te Wai Pounamu), Wales (Blaenau Ffestiniog), England (Derbyshire).

Māori Worldview Summary

• Framed by whakapapa.

• Whānau and whenua – identity grounded in familial relations, embedded in place identified by environmental features.

• Intergenerational perspective – non-linear perspective on time; past, present, and future inform decision-making.

• Wellbeing viewed holistically: social, economic, spiritual, and emotional are interconnected.

Mātauranga Māori

• Worldview: holistic, interconnected (e.g., Te Whare Tapa Whā).

Whakapapa

• Holism infers an interconnected relationship between all things: living and non-living, animate and inanimate, tangible and intangible.

• Identity, life meaning, and purpose intrinsically connected to:

  • Atua (God).

  • Whānau (family).

  • Whenua (land).

• Tupuna (ancestors) are connection points back to Atua; Whenua IS whānau.

• Whenua contain connection points to tupuna and Atua.

• Whānau: family and birth; Iwi: tribe and skeleton; Hapū: subtribe and pregnant; Whenua: land and placenta.

Mātauranga Māori as Indigenous Knowledge

• Oral culture based on local knowledge systems, therefore has regional (tribal and family) variations.

• Narratives hold principles, communicate values in memorable ways; use of multiple literary devices (poetic, metaphor, personification).

• Holistic, antithetical to categorization – in contrast to highly compartmentalized Western approach.

• Interconnectedness, interdependent relationships.

• Perspectives of mātauranga Māori have been impacted by colonization – infers a need for revitalization.

Māori Values

• Mauri: all animate and inanimate elements have a life force (energy).

• Mana: esteem, self-worth; we inherit and enhance our mana from contributions to community.

• Manaakitanga: to maintain and raise the mana of others; hospitality.

• Kaitiakitanga: from creation narratives, the earth is our mother, the forest, sea, and animals are her children – infers responsibility to look after them and natural resources.

• Rangatiratanga: self-determination.

• Tapu and noa: binary – tapu = restricted, noa = safe; remove tapu by karakia, kai, wahine.

• Rāhui: restriction, prohibition, unsafe.

Te Taiao: The Natural Environment

• Māori cosmology based on diverse narratives of creation that differ from area to area.

• Basic elements describe movements from stages of nothing, darkness to light; the separation of earth and sky and the emergence of life.

• Atua personify realms that demand respect and encumber humanity with responsibility of care and protection (tuakana/teina – humanity is the 'younger sibling' of nature).

• Vegetation, life forms, soil, minerals are considered to have agency; some now recognized in law with legal personality – not for exploitation but holding rights.

Te Urewera

• Te Urewera is ancient and enduring, a fortress of nature, alive with history; a place of spiritual value with its own mana and mauri.

• Te Urewera has an identity in and of itself, inspiring people to commit to its care.

Section 11 of Te Urewera Act 2014:

1. Te Urewera is a legal entity and has all the rights, powers, duties, and liabilities of a legal person.

2. Rights, powers, and duties must be exercised on behalf of Te Urewera by Te Urewera Board.

Te Awa Tupua (Whanganui River)

• "Ko au te Awa, ko te Awa ko au: I'm the River and the River is me."

• In 2017, Te Awa Tupua (Whanganui River Claims Settlement) Act was passed.

• The Act declares Te Awa Tupua a legal person and establishes the office of Te Pou Tupua.

• Te Kōpuka (river strategy group) established with 17 members including iwi, local government, commercial and recreational river users.

Taonga Tuku Iho: Treasure Handed Down

• "Everywhere my ancestors went they preserved and handed down the knowledge they had gained since creation."

• "This was always held to be a strict duty and was gone about very carefully and with much ceremony."

• Teone Taare Tikao (1890).

Te Waipounamu and Ngāi Tahu

Mana whenua:

• Holding responsibility for the mana of the land and occupants.

• Authority: responsibility of care.

Ngāi Tahu:

• Held mana whenua over greater part of Te Waipounamu since C18.

• Made up of 18 papatipu rūnanga (communities) centered around marae.

• Each rūnanga associated with a number of hapū (sub-tribes) – traditionally the primary social grouping, not iwi.

Ngāi Tahu Historical Context

• 1844–1864: 99% of Ngāi Tahu land sold to Crown for cash and for marking out adequate reserves, schools, hospitals, and access to mahinga kai (food sources) – none of which were provided.

• Ngāi Tahu ostracized politically, economically, socially; lost access to and transmission of cultural knowledge.

• Claim launched in 1849 and pursued relentlessly for 7 generations.

• 1986: Claim submitted to Waitangi Tribunal.

• 1996: Te Rūnanga o Ngāi Tahu Act passed.

• 1998: Ngāi Tahu Claim Settlement Act ($170m + 'bolt-ons').

• 2024: $1.7 billion net worth.

Ngāi Tahu Taonga Plants

• 55 native plants recognized under 1998 Ngāi Tahu Claims Settlement Act.

• Plants valued by Southern Māori for housing raw material, clothing, food, musical instruments, fine perfume.

• Harakeke (flax) – used for weaving.

• Tī kōuka (cabbage tree) – used for weaving sandals, rain capes; roots pounded to release sugars to add taste to food.

• Celmisia (mountain daisies) – used for adornments.

• Hinau – berries soaked in water to lessen bitter taste, provide ingredient for bread.

Ngāi Tahu Taonga Plants – Traditional Uses

• Karaka nuts: ground, carefully removing toxic poison, to make bread; trace of poison resulted in severe convulsions.

• Tutu: poisonous but could be distilled to make drink, edible jelly, and ink for moko.

• Kotukutuku (fuchsia tree): grows sweet berries; provided rare source of color blue; Māori girls painted their lips, youth painted their faces.

• Horopito (pepper tree): provided relief from toothache and headaches by chewing leaves; contains 4 active antifungals and powerful antioxidants.

• Koromiko (hebe): cured stomach aches and diarrhea.

Taramea (Wild Spaniard)

• Exquisite fragrance, prized perfume.

• Presented as gift, traded for food, ornaments, tools, or pounamu.

• Found in remote areas of Southern Alps.

• Taramea = 'spiny thing', prickly plant known to trampers and farmers as 'the wild Spaniard'.

• Leaves harvested by hand; aromatic resin extracted, sometimes by warmth of fire.

• Gum mixed with animal or vegetable oils, blended with scented plants.

• Ngāi Tahu invested in research on how to grow plant and extract oil; Taramea Fragrance Ltd formed.

Maraeroa C – Ginseng Project

• Māori land entity; land held by community.

• North of North Island; remote, difficult access.

• 75% agreement required from shareholders.

• Forestry block; 30+ years to mature.

• Partnership with Scion (Crown research institute).

• Ginseng: plant root from China/Korea with medicinal qualities.

• 8 years research and development.

• High quality, top-end product.

Titoki – Traditional Use

• Highly valued in Māori society.

• Pulp of berry is edible.

• Seed cultivated for its oil.

• Oil used to anoint the head – highly tapu.

• Often mixed with fats and oils from whales and sharks.

• Worn around the neck in a 'kopa' or pouch.

• Dried bird skin (e.g., toroa/albatross) soaked in oil, rolled, and worn around the neck.

Titoki – Timber and Oil

• Became known by European settlers as NZ oak; timber used for coach building, tool handles.

• Timber held in high regard by Māori; 'peka tōki' relates toughness of wood to a hardened leader or tribe.

• Grows naturally in coastal and lowland forest around many parts of NZ.

• Shiny black seed looks appealing but bitter tasting.

• Oil extracted from seed by Māori for body perfume.

Titoki – Oil Extraction Method

• Berries collected, placed in water, then trampled vigorously.

• Pulp separates from seed.

• Clean seeds pounded and crushed in harakeke (flax) woven vessels.

• Sometimes heated with hot rocks.

• Wrung by hand to extract oil.

Consultation

• (Title slide)

Consultation – Mahaanui Kurataiao Ltd and Rūnanga

• Ngāi Tūāhuriri Rūnanga.

• Te Hapū o Ngāti Wheke Rūnanga.

• Te Rūnanga o Koukourārata.

• Ōnuku Rūnanga.

• Wairewa Rūnanga.

• Te Taumutu Rūnanga.

Transgender Cosmetic Science

Learning Objectives

• Define: use accurate, current terminology for gender identity and gender-affirming care.

• Describe: explain how testosterone and estrogen + anti-androgen therapy alter sebum, hair, barrier function, and pigmentation.

• Identify: recognize skin conditions that disproportionately affect TGD individuals and post-surgical considerations for scar care.

• Apply: translate physiology into evidence-based personal-care formulation choices (actives, vehicles, claims, sensory).

• Critique: evaluate marketing claims aimed at TGD consumers against current evidence base and known gaps.

Key Statistics

• 0.5–1.6% of adults in recent national surveys identify as transgender or gender-diverse; proportion is higher among adolescents and rising.

• 1 in 11,900 (historic Netherlands data for transgender in genotypic men; 1 in 30,400 in genotypic women) – illustrates how older registry-based numbers under-count modern self-identification.

• 16.7–33% of trans women in US city-level surveys reported receiving illicit silicone or filler injections – major dermatologic concern.

New Zealand Census Data

• (Slide contains demographic data for census usually resident population aged 15 years and over)

Cisgender and Transgender Status by Identity

• (Diagram showing census data for cisgender and transgender status level 2)

Why the Cosmetic Scientist is in this Conversation

• Hormones rewrite skin in months: cross-sex hormones cause sebum, hair, hydration, and barrier properties to shift on a 4–12 month timescale – faster than most product reformulation cycles.

• Routines change with identity: transmasculine youth often disengage from skincare (associating it with femininity) exactly when testosterone begins to drive new acne – a formulation/marketing problem, not a clinical one.

• Hair removal is a cornerstone: facial hair elimination is consistently rated one of the most important – and most distressing – parts of feminizing transition; pre- and post-procedure care is a real product opportunity.

• Surgical adjuncts and scar care: top surgery, vaginoplasty, and phalloplasty leave scars; silicone-based scar products, sun protection, and ingredients for hypertrophic scars are highly relevant.

• Inclusion = safety: when mainstream products fail, consumers turn to unregulated alternatives (e.g., illicit injected fillers); good products with honest claims are a public-health intervention.

The Skin and Hair, on Hormones

• What changes, when, and why – the physiology a formulator needs.

Recap: How Androgens Drive the Pilosebaceous Unit

• Adrenal and gonadal androgens (DHEA-S, androstenedione, testosterone) reach skin via blood.

• 5α-reductase in sebocytes and dermal papilla → DHT (more potent androgen).

• DHT binds androgen receptor on sebocytes, dermal papilla cells, sweat glands.

• Results: ↑ sebum output, ↑ terminal hair on face/chest/abdomen, ↑ scalp follicle miniaturization in genetically susceptible sites.

Why this matters:

• Adding testosterone moves a person along same axis as endogenous puberty – more sebum, more terminal hair, scalp thinning.

• Adding estrogen + anti-androgen moves them the other way.

• Same biology serves many consumers: PCOS, perimenopause, prostate-cancer anti-androgen therapy, hypogonadism, anabolic steroid use.

• Sebum and acne shift in weeks; alopecia in years – product strategy should match timescale of change.

• Androgens unmask (do not create) follicle responsiveness; family history predicts who develops AGA on testosterone.

Testosterone in Trans Men: Acne is the Story

• Onset: 4–6 months after starting testosterone, peaking around 6 months.

• Distribution: face, chest, back; truncal acne climbs most steeply.

• Severity: usually mild-moderate; ~50% use a topical product within year 1.

• Many trans men remain on testosterone indefinitely – management must be sustainable, not a 12-week course.

• Severe/nodulocystic cases can respond to oral isotretinoin with usual cautions.

Hair: Gain at the Periphery, Loss at the Crown

Body and facial hair (desired):

• 100% of trans men in Wierckx (2014) reported increased facial and body hair on testosterone undecanoate.

• Ferriman-Gallwey ≥8 (clinical hirsutism range) reached by 80% at 12 months.

• Hair shaft diameter approaches but does not always match cisgender male values within a year – longer exposure may be needed.

• Product perspective: shaving, beard care, ingrown-hair management, post-shave irritation become 1st-time concerns.

Scalp/androgenic alopecia (often unwanted):

• 31% had moderate-severe AGA after mean of 10 years on testosterone.

• Older age and family history are strongest predictors.

• Topical minoxidil + low-level laser light therapy (LLLT) are FDA-approved options that do not interfere with masculinization.

• Finasteride is effective but blocks 5α-reductase (same enzyme driving beard growth) – often only considered after several years.

• Some trans men welcome male-pattern hairline; others find it distressing – ask, do not assume.

Estrogen + Anti-Androgen: Changes for Trans Women

Typical regimens (know names, not doses):

• Estrogen: 17β-estradiol valerate (oral) or transdermal estradiol patches; transdermal is less thrombogenic.

• Anti-androgens: spironolactone (US), cyproterone acetate (Europe), GnRH analogues, occasionally finasteride.

• In NZ/Australia: Spiractin, Aldactone, Spirotone.

• Adjuncts in skincare context: topical 5α-reductase inhibitors not standard of care; eflornithine (Vaniqua) HCl 13.9% reduces facial hair growth but causes acneform reactions in 10–20%.

What the skin does:

• Sebum: drops sharply by ~4 months; remains low at 12 months; existing acne usually improves.

• Hydration/barrier: reduced sebum → drier skin, occasional brittle nails; eczema-prone skin can flare.

• Body hair: hair-shaft diameter on legs, abdomen, cheeks falls within ~4 months; growth rate slows more gradually.

• Beard: resists androgen suppression – usually requires laser, electrolysis, or eflornithine.

• Pigment/cancer risk: some HRT data suggest modestly raised cutaneous melanoma risk; routine full-body checks recommended.

At-a-Glance: The Directions of Change

What Young Consumers Say About Their Skin

(Free-text responses from 2021 Seattle survey of 118 adolescents – Covelli et al., paraphrased)

• Trans man, 16: "I do not always do skin care because it is seen as a traditionally feminine thing and it can make me dysphoric." (Engagement gap)

• Trans man, 19: "Ever since starting hormones my acne got worse so I needed to start using face wash." (Cue to enter category)

• Cisgender female, 15: "I feel a greater pressure to keep my skin clean and clear. If my skin is more blotchy I feel worse about myself." (Common ground)

• Trans woman, 16: "Girls and women are expected to take better care of their appearance than men to fit society's ideal standard." (Marketing pressure)

Translating Physiology into Formulation

• (Section header slide)

5 Principles Before Any Specific Formula

1. Formulate for physiology, not identity: an anti-androgen-affected sebaceous gland behaves the same in a trans woman and a man on prostate-cancer therapy; group by skin state, not gender label.

2. Tolerance over potency, especially early: hormone-driven shifts coincide with high stress and frequent procedural disruption; gentle, redundant routines beat aggressive single-active stacks.

3. Multifunctional, sustainable rituals: many TGD consumers will be on hormones for years to decades; twice-a-week 'reset' actives outperform 12-week 'courses'.

4. Inclusive sensory and packaging: scent, color, font, claim language, and aisle all carry gender signals; make defaults neutral; offer customization.

5. Honest claims, professional referral: cosmetic claims must not promise medical or surgical outcomes; build referral pathways into education.

Toolkit A: Skin on Testosterone (Oily, Acneic)

Toolkit B: Skin on Estrogen + Anti-Androgen

Hair Removal: Where Formulators Add Value

Electrolysis:

• Permanent in skilled hands (~15–25% regrowth at 6 months).

• Side effects: erythema, PIH, scarring, HSV reactivation.

• Cosmetic-science angle: lidocaine creams, barrier creams, post-procedure soothing.

Laser and IPL:

• Reduces, lightens, and thins hair; rarely permanent.

• Best on dark hair/light skin; modern devices safer in deep skin tones.

• Cosmetic-science angle: pre-treatment sun-avoidance education, post-treatment cooling and barrier products, pigment management with niacinamide/azelaic acid.

Topical eflornithine:

• Reduces facial hair growth rate (FDA-approved).

• Effect reversible; results visible after 6–8 weeks.

• 10–20% develop acneiform reactions – formulator opportunity for compatible acne-tolerant moisturizer.

Sensory, Packaging, and Claims

Sensory:

• Scent: keep neutral or omit – traditional 'masculine' or 'feminine' fragrances trigger dysphoria.

• Color cosmetics: tints suitable across wider undertone range; concealer that covers beard shadow and post-laser pigment changes.

• Texture: lighter on face (sebum-shifted, often acneic), richer on body (xerosis-prone).

Packaging:

• Default to neutral, clinical, or ingredient-led design.

• Refillable/decant systems support customization without re-formulation.

• Clear typography; avoid gendered icons (pearls, beards) on primary packaging.

• Sample sizes that match procedure-course duration (e.g., 4-week trials).

Claims:

• Substantiate, then describe – never the other way around.

• Avoid medical/surgical promises ('replaces breast augmentation', 'permanent hair removal').

• If you list a TGD-relevant indication, ensure your panel included TGD users.

• Provide referral pathways in pack/QR copy: WPATH, dermatology, plastic surgery.

Case Study: Post-Procedure Soothing Serum

The brief: Design a leave-on serum for 24–72 h window after laser hair removal, suitable for face and chest. Target: TGD adults and cisgender women undergoing repeated laser sessions. Must be tolerated alongside SPF and gentle cleanser; safe with darker skin tones; cosmetic claim only.

Active strategy:

• 5% panthenol (barrier + soothing).

• 0.2% bisabolol or 0.5% madecassoside (anti-inflammatory).

• 2% niacinamide (PIH prevention).

• Trace allantoin (keratolytic + soothing).

• No retinoids, AHAs, BHAs, fragrance, or essential oils.

Vehicle and preservation:

• Light O/W emulsion or hydrogel; 70–80% water phase.

• Squalane + light esters as emollient.

• Hyaluronic acid (high + low MW) for surface and depth.

• Preservation: phenoxyethanol + ethylhexylglycerin; pH 5.0–5.5; no alcohol denat.

Claims and dossier:

• Cosmetic claims: 'soothes', 'comforts', 'reduces visible redness', 'supports skin barrier'.

• Substantiation: visual erythema scoring; TEWL recovery; user-perception study including TGD panelists.

• Avoid: 'prevents pigmentation', 'medical-grade', 'heals'.

• On-pack: 'compatible with laser and electrolysis aftercare'; QR to written instructions.

What We Still Do Not Know

• Pediatric and adolescent data: most evidence from adult cohorts; hormone-treated adolescents may respond differently.

• Comparative efficacy in TGD users: no head-to-head trials of standard acne or AGA actives specifically in TGD cohorts – extrapolate from cisgender data.

• Skin-of-color outcomes: most cited surveys are predominantly white; pigment management, laser parameters, and PIH risk in skin of color need more work.

• Long-term cancer signal: mixed melanoma and NMSC data with HRT; no long-term cohort focused on transfeminine populations.

• Sensory and consumer research: few published packaging/sensory studies with TGD panels; industry has data, little is shared.

• Real-world hair-removal aftercare: no comparative formulation trials of post-procedure cosmetics – cosmetic industry could lead here.

Ethics: The Boundaries of Cosmetic Care

• Designing well-tolerated, evidence-based daily care.

• Realistic, substantiated cosmetic claims.

• Inclusive consumer research, panels, and sensory work.

• Adjacent products to professional procedures (pre/post-laser, scar care, beard shadow camouflage).

• Education materials with clear referral pathways.

• Adverse-event monitoring with awareness of TGD-specific routes (e.g., hormone interactions).

5 Things to Take into the Lab

1. Hormones rewrite skin in months – sebum, hair, and barrier shift on a 4–12 month timescale that does not match standard product cycles.

2. Trans men gain acne and body hair, and may lose scalp hair; trans women gain dryness and reactive skin, and rarely lose facial hair without help.

3. Most relevant actives are already familiar: salicylic acid, retinoids, niacinamide, ceramides, panthenol, minoxidil, silicone for scars, SPF every day.

4. The product opportunity is rarely a 'trans range' – it is inclusive, hormone-aware design that quietly serves multiple consumer cohorts.

5. Honest claims, neutral sensory, and named referral pathways are part of the formulation – not afterthoughts.