Acid Mantle
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.