Everything You Ever Wanted to Know About Alpha Hydroxy Acid (a.k.a AHA)

So, what exactly are AHAs?

Alpha-hydroxy acids (AHAs for short) are natural and synthetic acids that exfoliate the top layer of your skin, leaving you with a smoother, brighter, more youthful-looking complexion. There are a number of different AHAs commonly found in skincare products: glycolic acid (which is derived from sugar cane), lactic acid (which comes from milk), mandelic acid is (which is derived from bitter almonds), citric acid (which comes from citrus fruits), malic acid (which also comes from fruits), tartaric acid (which comes from grapes), hydroxycaproic acid (which comes from jelly), and hydroxycaprylic acid (which comes from animals).

“Glycolic acid is the smallest alpha-hydroxy acid and the most popular of the AHAs, as it penetrates the skin easily,” says Jessie Cheung, MD, board-certified dermatologist. “Glycolic acid is commonly found in topical skincare products to gently dissolve the outermost dead skin cells to reveal fresh, glowing skin.” The second-most popular acid is lactic acid, which is a bit gentler than glycolic acid, making it a great go-to for those with sensitive skin. Often, you'll find formulas (like YOUTH TO THE PEOPLE Kombucha + 11% AHA Exfoliation Power Toner) that include both AHAs.

When it comes to AHAs, molecule size makes a big difference: “As the AHAs get larger in size, they don't penetrate as deep," says Dr. Cheung. She adds that glycolic acid is the most popular AHA because it has the smallest sized molecules. "The other AHAs, such as mandelic, lactic, and malic acid, are less efficient but more gentle.” she says.

What’s the difference between AHAs and BHAs?

While beta hydroxy acids and AHA work together well, they aren’t the same thing. The main difference between the two: “Salicylic acid (the most popular beta-hydroxy acid) is oil-soluble, and thus gets into your pores, unlike alpha-hydroxy acids, which are water-soluble (meaning they work on the skin's surface),” according to Dr. Cheung.

Because BHAs can penetrate pores, they're better at dissolving the dirt, bacteria, and excess sebum that gets trapped inside causing breakouts. That explains why it's a go-to ingredient in many acne-prone skincare routines.

The good news is, you don't necessarily have to choose between using BHAs or AHAs. To achieve maximum results, you might look for a skincare product that features both as active ingredients. “Combining different acids actually improves efficacy while decreasing irritation, [which is why] combination AHA/BHA products are popular,” says Dr. Cheung. Our go-to hybrid formula: GLOSSIER Solution, a toner that offers a balanced dose of both for glowing, breakout-free skin.

What are the benefits of AHAs?

Whether your biggest skin concern is acne, signs of aging, or an uneven skin tone, AHAs are able to help treat a long list of skin conditions. Here are a few of the top reasons we love these skincare superstars:

1. They're a gentler way to exfoliate.

While it is important to regularly slough away dead skin cells to keep the skin healthy, using physical exfoliation (i.e., face scrubs, facial brushes, etc.) can sometimes be too harsh or damaging to the skin.

Alpha hydroxy acids, however, exfoliate in a different way. They use a process called chemical exfoliation. While this might sound scary, it's actually much gentler. “Chemical exfoliation relies on acid to dissolve the attachments between skin cells, causing a controlled trauma to the skin to encourage cell turnover and reveal evenly pigmented skin,” says Dr. Cheung. Basically, AHAs "unglue" dead skin cells from the top layer of your skin, encouraging a smoother complexion without all the abrasiveness.

2. They'll brighten your complexion.

Often a dull skin tone is a result of dead skin cell build-up. So when you use AHAs to slough away that layer of dead skin, the new skin that's revealed from beneath will naturally be brighter and more radiant.

3. They're great for mature skin.

AHAs can be a gamechanger for fine lines and mature skin types in a number of different ways: As you age, the rate at which your skin cells turn over naturally slows down, causing more dead skin cells to accumulate on the surface of your complexion. As these build up, they can end up making signs of aging more apparent. But with the help of AHAs, you can remove that build-up and therefore minimize the appearance of things like fine lines.

Loretta Ciraldo, MD, FAAD, a Miami-based dermatologist and the founder of Dr. Loretta skincare, explains that AHAs like glycolic acid also have a unique ability to stimulate the skin's production of anti-aging superstars collagen and hyaluronic acid, both of which can plump up the skin, boosting elasticity and further reducing the appearance of fine lines.

4. They can promote a more even skin tone.

“Dead cells store excess pigment for many weeks,” says Dr. Ciraldo. As AHAs encourage faster cellular turnover, dark spots and hyperpigmentation caused by aging, sun damage, acne scars, age spots, or melasma will fade faster. Once the pigmented skin cells are exfoliated away, you'll notice a newer, more even-toned skin texture appear in its place.

5. They can help treat acne.

AHA's bestie BHAs (beta-hydroxy acids) are often considered a holy grail ingredient for acne-prone skin. While it's true that BHAs are better for penetrating pores to dissolve the gunk trapped inside, AHAs are still super helpful for preventing breakouts. The reason pores often get clogged in the first place is because dead skin cells prevent them from breathing properly. With AHAs, you can keep any build-up at bay, reducing the risk of blemishes.

What skin types can use AHAs?

AHAs are suitable for most skin types. “All but sensitive, post-procedure, and rosacea skin can use AHAs,” says Dr. Ciraldo. AHA products are also a safe alternative to BHAs (like salicylic acid) if you’re pregnant, breastfeeding, or trying to conceive.

When using AHAs, it’s best to incorporate them into your routine gradually, Dr. Cheung adds. “Start off with products with lower concentrations of active acid, and give yourself a few days before reapplication to see how your skin responds,” she says.

How do I add AHAs to my skincare routine?

To incorporate AHAs into your routine, you might start with a gentle toning formula (like PIXI BEAUTY Glow Tonic) that features 5-8% glycolic acid about three times per week. Once your skin has adjusted—and if you haven’t had any adverse reactions—you might bump that up to a stronger 10% formula (like THE INKEY LIST Glycolic Acid Toner) every other day.

For a super strong treatment, some people opt for an in-office chemical peel. Dr. Loretta says that during this treatment, 70% glycolic acid is often used. Obviously, this is a super strong concentration and you'll want to chat with your derm about whether or not this is right for your skin.

For skin that's more on the sensitive side, you might try wading into AHAs by starting with glycolic acid's gentler but still popular cousin lactic acid. Formulas like BIOSSANCE Squalane + Lactic Acid Resurfacing Night Serum and SUNDAY RILEY Good Genes All-in-One Lactic Acid Treatment are gentle enough to be used every day to every other day.

Do AHAs have any side effects?

As your skin builds up a tolerance to AHA products, you should also be on the lookout for any side effects. “It may cause redness, stinging, and even peeling in very sensitive or post-procedure skin,” says Dr. Ciraldo (P.S., by "procedure" she means skin peels).

Certain AHA formulas can also increase your skin’s sensitivity to the sun, so to avoid a sunburn you’ll want to be diligent about applying sunscreen daily if you’re using any acids in your skincare routine. But we're all doing that already anyway...right?

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