Skin sebum

The structure of the sebaceous gland can be imagined if you mentally press your finger on the skin and make a depression in it that reaches the dermis. Then the walls of the resulting pit will be lined with epidermis. The wall of the sebaceous gland really resembles the epidermis. It has a germinal layer in which continuous cell reproduction occurs, and just like in the epidermis, the topmost layer is the site of cell death. Only all this does not happen on the surface of the skin, but in the duct of the sebaceous gland. Unlike the keratinocyte, which accumulates keratin as it moves upward, the cell of the sebaceous gland accumulates a fatty secretion consisting of solid refractory fats. When the cell is destroyed, its contents splash out into the lumen of the sebaceous gland. Thus, the secretion of the sebaceous glands consists of sebum and fragments of sebaceous gland cells.

Once upon a time, in the distant past, when we were covered with hair, sebaceous glands were grouped around the hair. Hair, lubricated with fat, acquired shine, water-repellent properties, was less damaged by the sun and wind, and in addition, sebum, flowing along the hair, cleaned it from dust and dirt. These functions are still performed by the sebum of our smaller brothers. Every pet lover knows that a cat or a dog does not need to be washed (of course, with the exception of special cases), but it is enough to periodically clean their fur with a brush or scraper. In humans, most of the sebaceous glands are located at the base of the reduced hair follicles that produce vellus hair, so sebum from them mainly gets on the surface of the skin.

Normally secreting sebaceous glands provide softening of the upper layer of the skin, antimicrobial protection and partly help the stratum corneum to restrain water evaporation. The effect of sebum and cosmetics with a similar mechanism of action on the appearance of the skin is easy to understand if you imagine the upper layer of the skin under strong magnification. Here, the horny scales are ready to fly off the surface of the skin. Special enzymes have destroyed the bonds between them, and now the scales lie freely on the surface of the skin. Epidermal lipids are also practically absent here - too many factors (starting with daily washing with soap) contribute to their destruction. Therefore, the skin surface looks dry and dull (this does not necessarily indicate true dry skin). Sebum smoothes the horny scales, creating an even surface. Externally, the skin seems softer, more elastic and moisturized.

The same effect can be achieved by using special substances called emollients (from the English emollient - softening). Emollients are important ingredients in cosmetic creams, but their effect on the skin is usually short-lived. Currently, the cosmetic industry creates compositions that contain some components of sebum that have beneficial properties, in particular squalene and wax esters.

The production of sebum is regulated by male sex hormones - androgens. The higher the level of androgens in the skin, the faster the cells of the sebaceous gland multiply and the more sebum is released onto the skin's surface. Therefore, the skin of teenagers who experience hormonal storms during puberty often suffers from excess sebum production - seborrhea. The same affliction haunts women whose bodies produce too many male sex hormones.

[ 1 ], [ 2 ], [ 3 ]