See more

Search by skin concern, product name, type, texture, ingredients—pretty much anything.

See more

What Do Exfoliating Acids (AHAs and BHAs) Do?

The word “acid” has a negative—even scary—connotation, which may prevent some people from diving into acid-based skincare products. Here’s the thing, though: By avoiding acids, you skip some of the most effective and transformative skincare ingredients on the market. Acids are multi-beneficial; not only do they exfoliate by sloughing away dead skin and pore-clogging debris, but they also encourage cellular turnover, boost collagen production, and provide substantial brightening effects. Acids even allow other skincare products to penetrate deeper into the skin, working harder and faster than they would otherwise. No matter how daunting they sound, acids are safe, effective, and yes, a little misunderstood. It’s time to clear that up.

In skincare, acids can be separated into two categories: AHAs and BHAs, which stand for alpha hydroxy acids and beta hydroxy acids, respectively (the names refer to their chemical makeup). According to master facialist Sarah Akram and esthetician and StackedSkincare founder Kerry Benjamin, each category of exfoliating acid has its own distinct purpose. Read on for the difference between the two and how to use them.


AHAs, which are typically found in fruits, milk, and sugarcane, “exfoliate the skin’s surface, which is beneficial if you have dry or sun-damaged skin,” Akram says. “They dissolve dead skin cells and debris from the skin’s surface.” Depending on the specific acid that’s used, AHAs can treat everything from wrinkles to hyperpigmentation. These are the types of AHAs you'll often find in skincare: 

Glycolic Acid
Derived from fruit and sugarcane and included in skincare products to treat and reverse apparent signs of aging, Benjamin says glycolic acid is “great for treating fine lines and wrinkles and sun damage.” It’s also a go-to ingredient for improving skin texture and skin brightening. As such, it’s common to see it in preventative products for aging skin (like our Doctor's Visit Instant Resurfacing Mask)

Lactic Acid
Naturally, this acid is derived from milk (it can also be lab-created) for the purpose of treating “pigmentation, dry, or dehydrated skin, sensitive skin, and even eczema and rosacea due to its natural moisturizing effect on the skin,” Benjamin explains. Yes, even acids can be humectants, which draw moisture into the skin. Lactic acid is one of the most gentle, non-irritating AHAs—perfect for those that are just dipping their toes into the acids pool. For these reasons, we included it in The Shortcut Overnight Facial, which is specifically formulated with sensitive skin types in mind.

Citric Acid
Citric acid likely—and correctly—calls lemons, oranges, and grapefruit to mind, since it is present in citrus fruits. When it comes to skincare, however, Benjamin says citric acid is derived from corn or sugar beets. It’s mainly used to treat acne, sun damage, and superficial pigmentation issues. It can also be used as a natural preservative in skincare products. 

Mandelic Acid
Although less common than glycolic, lactic, and citric, mandelic acid is just as effective (especially for people who struggle with acne) thanks to its antibacterial qualities. Benjamin names the almond-derived acid a “great first-time chemical peel” since it doesn’t penetrate as far into the skin as other acids (like glycolic). Because it takes longer to penetrate the skin, there’s less of a chance that it will irritate sensitive skin.

Azelaic Acid
This one’s also particularly beneficial for those who struggle with acne and rosacea. It’s derived from rye, wheat, and barley, yet according to Akram, it’s actually gluten-free, making it suitable for those with celiac disease. It works by “decreasing swelling, redness and discoloration,” while “killing the bacteria that infect pores.” It also brightens and diminishes post-inflammatory hyperpigmentation (like dark spots) which is why it's found in our Weekend Glow Daily Brightening Solution.

Kojic Acid

This AHA was discovered (and is still popular today) in Japan. Derived from mushrooms and other fungi, kojic acid brightens, even skin tone, and reduces the look of fine lines by boosting collagen and elastin production. (Collagen and elastin are naturally present in our skin. They give it plumpness and that bounce-back effect.)


Beta hydroxy acids, on the other hand, are mostly known for treating acne because of its anti-inflammatory and antibacterial properties. Most importantly, this type of acid work at the pore-level (which is where breakouts form). 

Salicylic Acid
The most common BHA is salicylic acid, which is derived from willow tree bark. Benjamin loves this one because it deeply penetrates oil glands, making it ideal for acne-prone and oily skin. It actually dissolves excess sebum and other pore-clogging material, which keeps skin clear and bright. As such, you’re likely to see this ingredient in acne-fighting products, like our Nix It Complexion Solution, Keep the Peace Acne-Calming Cream Cleanser, and Back-Up Plan Acne-Control Body Mist. 

Can You Mix and Match Acids?

Combining acids can be incredibly beneficial—and yes, perfectly safe—since you're able to simultaneously treat various skin concerns. When combining acids, Akram says, “The main benefit is that you’re getting the best of both worlds that treat different and recurring skin issues.” Benjamin agrees. Multi-acid peels, like our Instant Resurfacing Mask, "are one of the safest and most effective ways to gently exfoliate and treat your skin,” she says. “Each acid has its own unique benefits. Combining multiple acids in one peel results in a one-stop shop for everything from acne, dark spots, dryness, redness, and even skin sensitivities like eczema and rosacea.” 

Curious about facial peels? Here's exactly how they work—no sting necessary.