Sebum

The device of the sebaceous gland can be imagined if you mentally apply a coat of cement on the skin and make it a depression that reaches the dermis. Then the walls of the resulting fossa will be lined with epidermis. The wall of the sebaceous gland really resembles the epidermis. In it there is a germ layer in which the continuous multiplication of cells occurs, and also, as in the epidermis, the uppermost layer is the site of cell death. Only this happens all not on the surface of the skin, but in the duct of the sebaceous gland. Unlike keratinocyte, which accumulates keratin as it moves upward, the cell of the sebaceous gland accumulates a fatty secret, consisting of hard refractory fats. When the cell is destroyed, its contents splash out into the lumen of the sebaceous gland. Thus, the secretion of sebaceous glands consists of sebum and fragments of cells of the sebaceous gland.

Once upon a time, in the distant past, when we were covered with hair, the sebaceous glands clustered around the hair. The hair, greased with bacon, acquired shine, water-repellent properties, was less damaged by the sun and wind, and besides, sebum, flowing along the hair, cleared it of dust and dirt. These functions are still performed by the sebum of our smaller brothers. Every pet lover knows that the cat or dog does not need to be washed (of course, except in special cases), but it is enough to periodically clean their hair with a brush or scraper. In humans, most of the sebaceous glands are located at the base of the reduced hair follicles that produce cannula hair, so the sebum from them mostly falls 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 horny layer to contain the evaporation of water. 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 top layer of the skin with a strong increase. Here the horny scales are already ready to fly off the surface of the skin. Special enzymes destroyed the bonds between them, and now the scales lie freely on the surface of the skin. There are practically no epidermal lipids - too many factors (starting with daily soap washing) contribute to their destruction. Therefore, the surface of the skin looks dry and dull (this does not necessarily indicate a true dry skin). The sebum smooths out 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 English emollient - softening). Emollients are important ingredients in cosmetic creams, but their effect on the skin is often short-lived. At present, the cosmetic industry creates compositions that contain certain components of sebum that have useful properties, in particular squalene and waxes 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 reproduce and the more sebum is released onto the surface of the skin. Therefore, the skin of adolescents experiencing hormonal storms during puberty often suffers from excess sebum production. The same misfortune persecutes women, whose body produces too many male sex hormones.

[1], [2], [3]