AHAs and BHAs are common chemical exfoliants found in cleansers, serums, and spot treatments. They’re both quick and effective at getting rid of dead skin cells, so they’re often thought of as the same. But AHAs and BHAs work differently on the skin — one is water soluble and the other is oil soluble — which affects how they tackle certain skin types and concerns. Understanding those differences is key for proper treatment. Here’s everything you need to know about these two acids and how to choose the one that’s best for you.
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What are AHAs?
Alpha hydroxy acids, or AHAs, are natural acids found in fruits, milk, and sugarcane. They’re water soluble, meaning they dissolve in water and can’t penetrate our skin’s natural oils to get to its deeper layers. Instead, AHAs do their work superficially on the top layers of the skin. When applied to the skin, they loosen the bonds between dead skin cells so that they’re replaced with new ones. These acids are also humectants, meaning they help attract and retain water in the skin, says Dr. Brendan Camp of MDCS Dermatology. Since they help with hydration, AHAs are great for normal to dry skin.
What are the benefits of AHAs?
Because they work on the surface layer, they smooth out skin texture, reduce dark spots or hyperpigmentation, and tackle fine lines and wrinkles through this surface-level exfoliation. So if you’re looking to brighten dull skin, treat sun damage, or reduce signs of aging, use AHAs. There are many different types of alpha hydroxy acids that are derived from varying sources and are optimized for different skin-care jobs. More on that next.
Which AHA should you use?
• Glycolic acid has the smallest molecule size of all the AHAs, so it easily penetrates the skin and exfoliates slightly deeper than other AHAs. That also means it’s more irritating than other AHAs with larger molecule sizes. It treats acne scarring, fine lines, hyperpigmentation, and sun damage.
• Lactic acid, which is a melanin suppressor, targets hyperpigmentation and sun spots. It’s also better tolerated than glycolic acid since it has a larger molecule size.
• Because of its antioxidant benefits, citric acid combats oxidative stress and helps brighten the skin. It slows dark-spot formation and improves signs of photoaging.
• If your skin is sensitive, start with mandelic acid. It has the largest molecular size of all the AHAs, so it’s the most gentle and least irritating of the bunch, and it helps to even out skin tone.
One thing to note, though, is if you have rosacea or eczema, you should consult your dermatologist or start with low concentrations first to see if you have any reactions. There are some cases where conditions worsen with the use of these acids, says Dr. Hope Mitchell of Mitchell Dermatology.
What are BHAs?
Beta hydroxy acids can be synthetic or naturally occurring acids that remove buildup of dead skin cells. They’re oil soluble, meaning they can pass through your skin’s natural oils and sebum to penetrate pores more deeply than AHAs and flush oil from pores. They also decrease inflammation and soothe redness. Unlike AHAs, which have a number of acids to choose from, “BHA is almost synonymous with salicylic acid,” says Camp. Tropic acid and trethocanic acid are two others, but they are rarely, if ever, used in skin-care products.
What are the benefits of BHAs?
Mitchell says BHAs are generally better tolerated than AHAs, since they have a larger molecular size than glycolic and lactic acids and are naturally antibacterial and anti-inflammatory. That also means they help calm down acne flare-ups. Because BHAs flush oil, they can address clogged pores, acne, blackheads, and whiteheads. With that said, they may not be best for dry skin since oil traps moisture into the skin, and BHAs’ oil-removing properties can be dehydrating for dryer types. But if you do have oily skin, Mitchell recommends incorporating BHAs in your morning routine to help manage oil levels throughout the day.
Can you combine BHAs and AHAs?
There are plenty of products out there that combine AHAs and BHAs, and they work particularly well for combination and mature skin. Dr. Kellie Reed at Westlake Dermatology in Austin points us to SkinMedica’s AHA/BHA Exfoliating Cleanser for tackling excess oil and discoloration, and Glossier’s Solution for acne and brightening. If you’re using separate products containing AHAs and BHAs, Mitchell recommends starting with low concentrations and using them on alternate days to prevent over-exfoliation and irritation. (If you’re looking for one for your skin type or concerns, we have an entire roundup of face exfoliators.) And as with any kind of exfoliation, following up every day with SPF is key since both increase sun sensitivity and make skin more prone to sun damage.
Which acid should you choose?
To sum it up, if you’re dealing with surface-level issues like dullness, uneven texture, anti-aging, or sun damage, AHAs are your best bet. They’re also great for normal-to-dry skin types. But if you have oily skin, clogged pores, or acne, go with BHAs. Used together, the two acids increase skin clarity, smoothness, and overall radiance, but be sure to start with low percentages and go slowly to avoid overdoing it.
Our experts
• Dr. Brendan Camp, dermatologist at MDCS Dermatology
• Dr. Adeline Kikam, Brown Skin Derm
• Dr. Hope Mitchell, dermatologist and founder of Mitchell Dermatology
• Dr. Kellie Reed at Westlake Dermatology in Austin
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