Understanding Skin Physiology: Glands, Emulsions, and Types

Sebaceous Glands

Sebaceous glands are associated with hair follicles and secrete sebum. They are composed of clustered, lobed structures that discharge their secretion to the skin surface. This sebum mixes with perspiration to form the epicutaneous emulsion. Each gland is surrounded by a membrane and separated by connective tissue, though they are not directly innervated by blood vessels. Their activity is regulated by androgen hormones.

Influencing Factors

• Abundance: Concentrated in the middle facial region, scalp, and upper back.
• Age: Sebum production begins at puberty, increases until age 50, and then begins to decrease.
• Sex: Men typically produce a higher quantity of sebum than women.

Sweat Glands

Sweat glands are tubular structures located deep in the dermis or hypodermis, discharging their secretion through a long canal. They consist of two main parts:

• Glomerulus (Secretory Coil): The coiled area containing sweat-producing cells, located in the dermis or hypodermis.
• Sweat Ducts: The channel that connects the glomerulus to the skin surface via a pore.

Types of Sweat Glands

• Eccrine: These pour their secretion directly onto the skin surface. They are found almost everywhere, except for areas like the nail beds or lips, and are abundant on the palms and soles. The sweat is 99% water with dissolved inorganic and organic substances, maintaining an acidic pH of 4.2 to 5.5.
• Apocrine: These discharge their secretion into hair follicles, where it mixes with sebum. They are present in the axillae, anogenital region, and mammary areola. The glomerulus is larger than that of eccrine glands and is located in the hypodermis. The sweat has a viscous, milky appearance and a neutral pH, which allows bacteria to decompose it, resulting in an unpleasant odor (as the sweat itself is odorless).

Epicutaneous Emulsion

The hydrolipidic film overlying the skin is formed by the mixture of sebaceous and sweat gland secretions, combined with sloughed epidermal corneal cells.

• Aqueous Phase: Formed by sweat and its dissolved substances.
• Oleous Phase: Composed of sebum and its dissolved substances.
• Emulsifier Phase: Unites the previous two phases to provide stability. The pH of this emulsion is typically 5.5.

Skin Types

• Normal: Does not shed, tans well, tolerates soap, appears matte or slightly shiny, and is smooth, soft, elastic, and flexible.
• Alipo (Dry): Dull, thin, rough, and dry to the touch. Prone to redness and scaling; does not tolerate sun, cold wind, or harsh soaps.
• Hyperhydrate: Bright, smooth, moist, and cold to the touch. Does not shed; tolerates sun and soap but is sensitive to adverse weather.
• Fat (Oily): Bright, thick, and greasy to the touch with visible pores. Tolerates sun, atmospheric changes, and soap.
• Fat Dehydrated: Bright with some fissures, thick, dry, and rough. Prone to early aging and peeling; moderate tolerance to sun but does not tolerate atmospheric extremes or soap.