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The acid mantle of the skin
Last reviewed: 04.07.2025
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The surface of normal skin is acidic, with a pH of 5.5 (neutral pH is 7.0, and blood pH is 7.4). Almost all living cells (including most bacterial cells) are very sensitive to changes in pH, and even slight acidification is harmful to them. Only skin covered with a layer of dead keratinized cells can afford to be clothed in an acid mantle (also called the Marchionini mantle).
The acid mantle of the skin is formed by a mixture of sebum and sweat, to which organic acids are added - lactic, citric and others. These acids are formed as a result of biochemical processes occurring in the epidermis. The acid mantle of the skin is the first link in the defense against microorganisms, since most microorganisms do not like an acidic environment. And yet, there are bacteria that constantly live on the skin, for example, Staphylococcus epidermidis, lactobacilli. They prefer to live in an acidic environment and even produce acids themselves, contributing to the formation of the acid mantle of the skin. Bacteria 5. epidermidis not only do not harm the skin, but even secrete substances that have an antibiotic-like effect and inhibit the vital activity of pathogenic microorganisms.
Frequent washing with alkaline soap can destroy the acid mantle. Then the "good" acid-loving bacteria will find themselves in unfamiliar conditions, and the "bad", acid-sensitive ones will gain an advantage. Fortunately, the acid mantle of healthy skin is restored fairly quickly.
Skin acidity is disturbed by some skin diseases. For example, with fungal diseases, the pH increases to 6 (slightly acidic reaction), with eczema -1 to 6.5 (almost neutral reaction), with acne - up to 7 (neutral).
It is interesting that the pH gradually increases as you "go deeper" into the epidermis at the level of the basal layer of the epidermis, where the germ cells are located, it becomes equal to the pH of blood - 7.4. The activity of enzymes working at different levels of the epidermis depends significantly on the acidity of the environment around them. Thus, enzymes involved in the assembly of the lipid barrier in the stratum corneum will work worse with an increase in pH as a result of frequent washing with soap. Another interesting observation - when the pH deviates from 5.5 in one direction or another, the organization of the lipid layers suffers: defects appear in them through which water can evaporate. Accordingly, if you abuse detergents (including the most traditional - bar soap), washing with or without reason, then the barrier function of the skin will be weak, since the stratum corneum will not have time to recover.
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