THE PH OF THE SKIN
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The pH scale is a measure of the acidity or alkalinity of a solution. The term pH was introduced in 1909 by the chemist Sørensen .
The pH takes values between 0 (strong acid ) and 14 ( strong base ) . The intermediate value 7 corresponds to neutrality , typical of pure water at 25 ° C.
The pH can be measured by electrical , exploiting the potential created by the difference in hydrogen ion concentration on two sides of a glass membrane , or by chemical , exploiting the ability of some substances to change their color as a function of pH detected . The indicators are often in the form of strips of paper that change color when dipped in acid or basic substances .
The pH of human skin is around to physiological values tend to be acidic , ranging between 4.2 and 5.6 , with peaks up to neutrality. The width of this interval can be explained on the basis of a great many factors that influence the pH of the skin : for example, varies according to the region of the body considered , season , sex, stage of the menstrual cycle, cosmetics and detergents used , the resident bacterial flora and the degree of sweating.
Oily skin or unclean has higher values , lower dry skin . This measure provides information on the use of cosmetics pH regulators and the effect of products capable of change
The acidity of the pH of the skin is linked to the presence of the hydro-lipid film and the plurality of the biochemical processes that occur in the skin . The hydrolysis of skin lipids to free fatty acids, is without doubt the main phenomenon responsible for the acidity skin . The adjustment of the pH of the skin also participates in the so-called mantle water , given by the sweat , the substances dissolved in it ( minerals , lactic acid, urea, ammonium ) and by transpiration
The pH of the skin contributes to defense against unfriendly microorganisms . An increase in the pH of the skin may therefore favor the development of fungal -bacterial infections . A slightly acidic pH of the skin also favors the activity of enzymes responsible for skin renewal and maintenance of some components of the skin.
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