Alpha-hydroxy Acids (AHAs)
This group of natural-based acids found in a vast number of skin-care products includes glycolic, lactic, citric, and tartaric acids. Glycolic acid was the original AHA and remains popular for its ability to remove dead skin cells and leave skin smoother, softer, and more radiant.
AHAs are used to exfoliate the skin, reducing fine lines, age spots, acne scars, and irregular pigmentation. Peels with high concentrations of AHAs are usually administered by a beauty specialist (esthetician) or dermatologist, but you can use lower concentrations -- between 5% and 10% -- in creams or lotions on a daily basis.
To help avoid irritated skin, start with a low concentration and apply every other day gradually increasing frequency to every day.
Even at lower doses, however, the acids may irritate and dry skin as well as increase sensitivity to the sun. Doctors recommend using moisturizer and sunscreen when using any products that contain AHAs.
Salicylic acid is used in many over-the-counter and prescription products to treat acne. It penetrates pores and reduces blackheads and whiteheads with less irritation than may occur with alpha-hydroxy acids. Like AHAs, salicylic acid in certain amounts exfoliates the skin, which can reduce signs of aging.
If you are allergic to salicylates (found in aspirin), you shouldn't use salicylic acid. If you are pregnant or nursing, you should ask your doctor before using any product with salicylic acid. Also be aware of symptoms of rare but serious allergic reactions. Seek emergency medical help if you have throat tightness, difficulty breathing, feeling faint, or swelling of the face or tongue. Also stop using the product if you develop hives or itching.
Hyaluronic acid is included in skin care products to reduce the signs of aging. Your body produces hyaluronic acid naturally, keeping tissues cushioned and lubricated. It's found in skin, joint fluid, and connective tissues. Age, smoking, and an unhealthy diet cause you to make less of it over time.
Products containing hyaluronic acid may help smooth out skin. It's especially effective when combined with vitamin C products.