Skin pH is a chemist's term meaning "potential of hydrogen" (a logarithmic measure of hydrogen ion concentration) and used to measure the degree of acidity or alkalinity in the outer skin layers. The pH scale ranges from 0 to 14, where 7 is neutral (neither acid nor alkaline), below 7 indicates an acid (a reading of 1 reflects the strongest acid) and above 7 indicates a base (14 represents the strongest base). A pH level can be used to show the acid/alkaline values of skin and certain skin care products.
Skin's natural pH, between 5.5 and 6.5, is slightly acidic (the acid mantle protects this barrier) while the pH of the majority of Earth's waters is above 7.0, making them slightly alkaline and incompatible with the pH of human skin. The pH scale works in 10-fold multiples and each pH unit represents a 10-fold difference in alkalinity or acidity. Example: soap with a pH of 11.5 has 10 times the alkalinity of a soap with a pH of 10.5. "Mild" soaps are often alkaline and remove the natural acid protection as well as extract protective lipids (fats) from the skin. Irritated and eczematous skins tend to have a more alkaline pH, and washing with soap can increase this alkaline state, creating a more vulnerable environment leading to further irritation and infection.
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