The Hydrolipid Film
The skin surface is covered with what is called a hydrolipid film - an emulsion of water (hydro) and fat (lipos). Its main function is as an external barrier to defend against bacteria and fungi. In addition, it keeps the skin supple.
In healthy skin the balance between oil and moisture is intact. The hydrolipid film varies in quantity and composition depending on the body region as well as exogenous and endogenous factors such as the time of day, the season and air humidity or nutrition, stress and illness.
Composition and function of the hydrolipid film
Composition of the hydrolipid film
Analysis of the skin structure and the keratinization process (i)shows that the following substances are present on the skin surface:
- Sweat and sebaceous lipids
- Substances from the cornification process (protein degradation products)
- Horny cells still in the shedding process
- Water from the deepest layers that has reached the surface (transepidermal water (i), insensible perspiration)
These components form the skin's continuously renewed protective film.
2 Sebaceous lipids
3 Corneocytes still in the shedding process
4 Cells in the cornification process
5 Transepidermal water
Importance of the hydrolipid film
One function of the hydrolipid film is to repel invaders. At the same time it maintains the suppleness of the skin. Due to the presence of weakly acid components such as lactic acid, pyrrolidine carboxylic acid and amino acids, the hydrophilic portion of the hydrolipid film forms a protective acid mantle (i).