What is it? Alpha hydroxy acids or AHAs are natural acids derived from fruit, milk or sugar cane, which dissolve dead skin cells and allow fresh, healthy cells to emerge. With so many kinds of AHAs, including glycolic, lactic, citric, mandelic and malic acids, the degree of exfoliation depends on the particular acid and its pH level.

After exploding onto the market in the 1990s as an anti-aging breakthrough, these natural exfoliators are now included in one out of every 17 skin care products, including almost 10 percent of moisturizers and 6 percent of sunscreens, according to a 2004 report from the Environmental Working Group.

Because of their ability to boost cell regeneration, AHAs are used for everything from fine lines and wrinkles to acne and age spots. Dermatologists and other skin care professionals use higher doses of up to 70 percent for chemical peels.

According to the Skin Care Guide, AHAs, especially glycolic acid, are also effective in improving pigment and melasma. The guide also states that AHAs seem to affect the cells beyond the first layer, which suggests that the benefits surpass exfoliation.

Aside from retinoids, AHAs also boast well-established efficacy. For example, researchers at Massachusetts General Hospital found that creams with 8 percent lactic acid and 8 percent glycolic acid improved the overall appearance of skin among 74 women, ages 40 to 70, with signs of photodamage.

You'll find it in: Many cleansers, lotions, acne treatments and anti-aging serums contain AHAs. The most popular AHA, glycolic acid, is frequently used in creams and lotions. Also, lactic acid is used in moisturizers because of its powerful hydrating properties. Mandelic acid, extracted from the bitter almond, is one of the least irritating AHAs and helps improve skin's overall appearance and texture. Derived from fruit, malic acid is also moisturizing and soothes dry and itchy skin.

Our product picks: For a no-nonsense anti-aging routine, try MaMa Lotion, a gel-lotion that packs a one-two punch with 10 percent mandelic acid and 10 percent malic acid. In addition to fading age spots and acne scars, MaMa Lotion also tightens the skin, erases fine lines and evens skin tone. MD Skincare Alpha Beta® Daily Face Peel/2 Steps is another product that helps improve clarity and tone while moisturizing and protecting the skin. With a blend of alpha and beta hydroxy acids, moisturizers, green tea extract and antioxidants, the pads stimulate collagen production and firm skin. The product also reduces pore size and treats acne and rosacea.

What to expect: It typically takes about two weeks to see a change in your skin, and it's important to continue using the product, because the results are cumulative. So how will AHAs improve your skin?

Our skin is made up of layers of dead skin cells that form a barrier around fresh cells, causing a dull complexion and clogged pores. AHAs are different from granular scrubs in that they actually dissolve the protein bond that connects the dead cells to healthy cells. Once the outer layer is removed, a brighter skin tone and improved texture is revealed. For instance, when using a glycolic acid for acne, the acid penetrates the pores and fights the bacteria that cause your breakouts. It also helps with inflammation and reduces the oil below the skin's surface.

In addition, as the AHAs exfoliate the skin, sun spots and blemishes fade, and topical treatments like moisturizers, acne creams and serums are better able to penetrate the skin.

Prior to using AHAs, consult with your dermatologist about the best product for you, and make sure to always test a small area of skin to see if you're sensitive to the product. Also, apply additional sunscreen; since AHAs remove dead skin cells at a fast rate, skin becomes more susceptible to damage from UVA and UVB rays.

Who should avoid it: People with sensitive skin should avoid products with a high concentration of glycolic acid, which can irritate and dry the skin. Most other AHAs are appropriate for all skin types, but the general rule is to start with a small amount to see how your skin reacts. If this is your first time using an AHA product, start with one application every other day and gradually increase as your skin becomes accustomed to the product.

See also:

Salicylic Acid

Lactic Acid

Glycolic Acid