The surface of normal skin has an acid reaction, and its pH is 5.5 (neutral pH is 7.0, and the pH of the blood is 7.4). Almost all living cells (including most of the bacterial cells) are very sensitive to pH changes, and even a small acidification is fatal for them. Only the skin, covered with a layer of dead keratinized cells, can afford to be clothed in an acid mantle (it is also called the mantle of Marcionini).
Acidic mantle of the skin is formed by a mixture of sebum and sweat, in which organic acids are added - lactic, lemon and others. These acids are formed as a result of biochemical processes taking place in the epidermis. Acid skin mantle is the first link of protection against microorganisms, since most microorganisms do not like acidic medium. 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 "good" acid-loving bacteria will find themselves in unusual conditions, and "bad", acid-sensitive, will have an advantage. Fortunately, the acid mantle of healthy skin is recovered fairly quickly.
Acidity of the skin is disturbed by certain skin diseases. For example, in fungal diseases, the pH rises to 6 (weakly 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 the epidermis "deepens" at the level of the basal layer of the epidermis, where the germ cells are located, it becomes equal to the blood pH - 7.4. The activity of enzymes working at different levels of the epidermis depends significantly on the acidity of their environment. So, the enzymes involved in assembling the lipid barrier in the stratum corneum will work worse when the pH is increased as a result of frequent soap washing. Another interesting observation is that if the pH is changed from 5.5 to one side or another, the organization of the lipid layers suffers: defects appear in them, through which water can evaporate. Accordingly, if you abuse the detergent (including the most traditional - lumpy soap), washing for and without reason, then the barrier function of the skin will be weak, because. The stratum corneum will not have time to recover.
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