Skin pH

The acid mantle helps suppress odor-producing bacteria on the skin. Restoring the skin's acidic environment is a primary goal of topical eczema treatment. The skin's natural pH is 5.5, placing it firmly in the acidic range. The acid mantle is a slightly acidic film on the skin with a pH between 4.5 and 5.5. The pH scale is logarithmic, with each whole-number step representing a 10-fold change in acidity. Healthy skin is naturally acidic. The skin's acidic environment is an immune defense that prevents harmful microbes from colonizing the surface. Sweat and sebum on the skin surface have a pH of 4 to 5.5, making them more acidic than the skin baseline. Post-menopausal skin has a thinner, slower-recovering acid mantle because sebum production declines after menopause. When skin pH rises, odor-producing bacteria can rapidly colonize the skin surface. Common skincare products such as lotions, detergents, and soaps are alkaline and can worsen eczema by disrupting the skin's acid mantle.