The hydrolipid film

The hydrolipid film is also known as the acid mantle. Its main constituents are sweat, sebum and keratin cells, and it ensures the correct balance of the skin flora. The sebaceous and sweat glands supply it and continually coat the skin with a water/oil emulsion. The main components keep the pH at, ideally, 5.5.

The pH indicates the concentration of hydrogen ions in an aqueous phase. The scale ranges from 0 to 14, with 0 being strongly acid, 7 neutral and 14 strongly alkaline (basic). 

Besides the keratinized cell layers, the acid mantle plays an essential part in protecting the skin and supplying moisture. It lies directly on the keratin layer, the outwardly visible layer of the epidermis, and has an antimicrobial effect, giving protection from alkaline and acid substances. If the acid mantle is intact, the bacterial decomposition of the components of sweat is kept low.