The pH scale measures the acidity or alkalinity of a substance. Your skin has a pH measurement too. When substances with different pH levels come into contact, chemical reactions often occur. The soaps, lotions and other products you use can have an effect on the pH, and thereby the health, of your skin. Understanding the potential effects can help you avoid irritation and other problems.
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PH and Your Skin
The pH of a substance is measured on a scale of 0 to 14, with 0 being the most acidic and 14 being the most alkaline. 7 is neutral, the pH of pure water. Each number on the scale is 10 times as strong as the number preceding it. Normal adult skin is somewhat acidic, having an approximate pH range of 4 to 6. According to "Ask A Scientist," this low pH is caused by carbon dioxide in the air.
The surface of the skin is coated with a combination of skin oil, called sebum, and perspiration. This coating is called the "acid mantle," writes Dr. Loren Pickart in an article on Skin Biology. According to Pickart, the acid mantle protects the skin from damage, including sun and wind exposure, and from dehydration. It inhibits the growth of bacteria and fungi, reducing your risk of acne, allergies, blemishes and other skin problems.
On "Ask A Scientist," Jim Swenson writes that alkaline substances with a pH higher than 8 can be very irritating to the skin, as can acids with pH levels of 3 or below. "Lemon juice has a pH of roughly 2.3," he writes. "You could wet a spot on your arm with that, let it dry, and in a little while, it will itch." Pickart adds that exposing your skin to an alkaline substance can make it more vulnerable to irritation and infection, including acne.
Hygiene and Skin PH
According to Pickart, even "mild" soaps can have a pH or 9 to 11. They can remove your acid mantle and extract protective lipids from your skin. If you have naturally dry skin or suffer from eczema, your skin has a more alkaline pH, in which case these soaps can increase your levels of irritation. In fact, a 2002 study published in the International Journal of Dermatology found that "most products recommended for sensitive skin have a considerable irritation effect, which is related to the pH of the product."
"Ask A Scientist" recommends that you test products on your own skin to find out how they work for you. You can also lower the pH of your lotion or hand soap by adding citric acid (lemon or lime juice). At "Yin Yang Skin Science," professor Desmond Tobin recommends using acidic topical skin care products to reduce dryness and sensitivity. The scientific study published in the International Journal of Dermatology concludes that people simply need better information on the pH of a product so they can use it appropriately.