With the concept of the protective acid mantle , the relationship between the measured weakly acidic pH value of the epidermis and the bactericidal effect of the secretions formed by the skin glands (especially sweat and fatty acids ) was explained. The measured pH value of 5.5 in humans is supposed to protect against pathogens in the same way as a coat .
The term “acid mantle of the skin”, which later became the protective acid mantle ( hydrolipid mantle ), goes back to the work of the physician Alfred Marchionini , who, together with his teacher Heinrich Schade, wrote an article in the Klinische Wochenschrift in 1928 with the title: The acid mantle of the skin (after glass chain measurements) published. By measuring the concentration of hydrogen ions, they found that the surface of the skin was covered by a layer of acid. However, this finding was not entirely new. Ernst Heuss had already made this statement in 1892 . Marchionini was the first to establish a connection between measured acidic pH values and bacterial colonization of the skin. It was emphasized that “the body uses the same means of defense against bacteria in three places as different as the stomach, vagina and skin”.
In-vitro studies later raised considerable doubts as to whether the measured pH alone contributed to the defense against bacteria. Pillsbury and Rebell measured equally good growth of Staphylococcus aureus at pH 5, 6 and 7. Further investigations came to the conclusion that the milieu pH does not influence the number of skin germs, but its enzymatic activity. The fatty acids contained in sweat, which are most effective at pH 5, are also decisive for the antimicrobial effect. Eventually it was recognized that solvent extracts from human skin mainly contain bactericidal lipids and peptides (such as beta-defensin), which are able to kill hemolytic streptococci and other gram-positive bacteria .
Influence of skin cleansers
The concept of the protective acid mantle was mainly taken up and marketed by the advertising industry. Synthetic detergents should “protect” (or restore) the protective acid mantle better than alkaline soaps. Many components of the protective acid mantle, such as lactic acid, uric acid or fatty acids, are washed off with the water without the aid of detergents because of their good solubility in water. The opinion quickly spread that if the skin was cleaned too intensively and frequently with (too hot) water and cleaning agents such as B. curd soap the protective acid mantle of the skin can be "destroyed" and the skin flora is out of balance. Scientific studies put this widespread opinion into perspective, however. A longer-lasting influence on the pH value of the skin surface could not be achieved even with prolonged use of soap, since the skin surface pH shift in healthy skin regresses within an hour after washing. In small children and old people, however, the skin has a lower alkaline neutralization capacity, so that it takes up to three hours for them to reach the acidic pH value again.
The problem with skin cleansing is the disturbance of the healthy skin flora, since some of the microorganisms that act as placeholders, as well as lipids and other substances necessary for maintaining the skin barrier, are released from the skin and rinsed off.
- H. Schade, A. Marchionini: The acid mantle of the skin. In: Klin Wochenschr . Volume 7, 1928, pp. 12-14.
- E. Heuss: The reaction of sweat in healthy people . In : months practical dermatol. Volume 14, 1892, pp. 343, 400, 501.
- DM Pillsbury, G. Rebell: The bacterial flora of the skin; factors influencing the growth of resident and transient organisms. In: Journal of Investigative Dermatology . Volume 18, Number 3, March 1952, pp. 173-186, . PMID 14908192 .
- EJ Foley, F. Herrmann, SW Lee: The effects of pH on the antifungal activity of fatty acids and other agents; preliminary report. In: Journal of Investigative Dermatology. Volume 8, Number 1, January 1947, pp. 1-3, PMID 20285130 . .
- H. Pösl, CG Schirren: Influence of the pH value of the skin surface by soaps, detergents and synthetic detergents. In: The dermatologist . Volume 17, 1986, pp. 37-40.
- Wolfgang Raab: Structure of the skin. In: Wolfgang Raab, Ursula Kindl: Care Cosmetics: A Guide. Wissenschaftliche Verlagsgesellschaft, Stuttgart 2012, p. 10. ISBN 978-3-8047-2761-8
- Aspects of skin tolerance, skin protection and skin care. Epidemiological Bulletin No. 18, Robert Koch Institute, May 4, 2015; accessed on December 20, 2019