Our skin is constantly renewing itself, growing new skin cells to replace the surface skin cells that grow old, die, and fall, or slough, off. Every minute of every day, between 30,000 and 40,000 dead skin cells flake away. Factors like age and dry skin can mean that dead skin cells don’t fall away as easily as they should. When these cells build up, they can make the complexion look rough and pasty and can also contribute to the clogged pores that lead to adult acne. The regular yet careful use of a skin exfoliant can help slough off dead skin cells and uncover fresh, more youthful skin.

There are two main types of skin exfoliants: mechanical exfoliants and chemical exfoliants. Both are commonly available, and both have pros and cons regarding their use and the types of skin conditions for which they are most appropriate.

Mechanical Skin Exfoliants Mechanical exfoliants work by sanding off dead skin cells using mildly abrasive substances. These skin exfoliants typically are facial scrubs, creamy cleansers with tiny, rough particles. As you gently massage the exfoliant over the surface of your face and skin, the friction works to loosen the old skin cells.

Mechanical skin exfoliants are readily available in drugstores and easy to use. They are particularly good for people with oily skin or acne, as they remove skin cells and debris that clog pores, but only if you don't scrub too hard as this can cause further irritation.

However, mechanical exfoliants can be harsh. When you use them, you're literally sanding away the outer layer of your skin. Some contain particles so jagged and rough that they could actually cut the skin. Because of this, dermatologists recommend using a gentle motion when using a skin exfoliant, and skipping them altogether if you have sensitive skin.

Mechanical Skin ExfoliantsA chemical skin exfoliant uses gentle acids to dissolve whatever bonds are preventing the outer layer of dead skin cells from falling off your face and body. There are two main types of chemical skin exfoliants, those that include an alpha hydroxy acid (AHA) and those that include a beta hydroxy acid (BHA):

• Alpha hydroxy acids are derived from different foods, from fruits, such as apples and grapes, to milk. Some of the most common AHAs to look for on product labels are glycolic acid, lactic acid, malic acid, alpha-hydroxyoctanoic acid, and triple fruit acid. An alpha hydroxy acid is best for people with dry or thickened skin.
• Beta hydroxy acids are the chemical cousins of alpha hydroxy acids, but are more oil-soluble and therefore better at exfoliating oily skin or acne-prone skin. The best known beta hydroxy acid is salicylic acid. On product labels, look for salicylate, sodium salicylate, beta hydroxybutanoic acid, or tropic acid.

Alpha hydroxy acid and beta hydroxy acid skin care products tend to be less harsh on the skin than mechanical exfoliants. They also help refresh the skin in ways a facial scrub can't: They lower the skin's pH level and help smooth small, shallow wrinkles, improving the look of skin that is dry or sun damaged.

Finding the right formulation for your skin involves some trial and error. According to the U.S. Food and Drug Administration, you should choose alpha hydroxy acid-based chemical exfoliants with an alpha hydroxy acid concentration of 10 percent or less and a pH of 3.5 or more. Beta hydroxy acid-based exfoliants containing salicylic acid are effective at levels of 1.5 to 2 percent. Using stronger solutions can cause skin irritation.

Another caveat: These types of exfoliants increase your skin's sensitivity to the sun for as long as a week after each use. Before going out, always apply sunscreen — a skin-saving recommendation for everyone.

How and When to Use Exfoliants You should not use an exfoliant every day. Your skin needs time to regenerate its topmost layer, which exfoliation strips away. People with dry skin should only exfoliate once or twice a week, while those with oily skin can exfoliate two to four times a week. Stop using an exfoliant if you find your skin becoming irritated or developing a rash. Remember to moisturize your skin after exfoliating, to soothe it and keep it from drying out.