Dr. Jane Yoo, a board-certified dermatologist, breaks down AHAs and BHAs: how they differ in solubility, which acids work best for aging versus acne, and why you need sunscreen daily when using them. She covers glycolic and lactic acids for texture, salicylic for oiliness, and whether to alternate or combine exfoliants.
Hi everyone, I'm Dr. Jane Yoo, board-certified dermatologist and Mohs surgeon. Today I want to break down the difference between AHAs and BHAs, two of the most commonly used chemical exfoliants in skincare, and explain how they connect to chemical peels. To start, AHA stands for alpha hydroxy acid and BHA stands for beta hydroxy acid. Both are chemical exfoliants meaning that they work by dissolving the bonds that hold dead skin cells together, helping the skin shed those cells more effectively. This is different from physical exfoliation, which uses scrubs or tools to manually buff away dead skin. Chemical exfoliation tends to be more controlled and even, and when done correctly, it can produce significant improvements in skin texture, tone, and clarity. The actual difference between AHAs and BHAs comes down to one key distinction, which is their solubility. AHAs are water soluble, which means that they work primarily on the surface of the skin. BHAs are oil soluble, which allows them to penetrate deeper past the surface and into the pores themselves. The difference in how they travel through the skin is what determines which concerns each one is best suited to treat. AHAs are naturally derived from sources like sugarcane, milk, and fruit. The most commonly used AHAs in skincare are glycolic acid and lactic acid. Glycolic acid has the smallest molecular weight of all the AHAs, which allows it to penetrate the skin most easily and effectively. It is a strong all-around exfoliant and is often used to address fine lines, surface wrinkles, uneven skin tone, and sun damage. Lactic acid is another popular AHA that also has mild hydrating properties, making it significantly gentler option that is well suited for improving texture and softness. Other AHAs you may see listed on labels include citric acid, mandelic acid, malic acid, and tartaric acid, although glycolic and lactic are by far the most widely used. BHAs, on the other hand, work a bit differently. The most common BHA used in skincare is salicylic acid. It was first isolated from the bark of willow trees in the Salix genus, which is where it gets its name, and it also occurs naturally as a free acid or as esters in many plant species. Species. Because BHAs are oil soluble, they're able to penetrate deeper into the skin, traveling down into hair follicle and pore rather than staying on the surface. This allows them to dissolve excess sebum and break up the buildup of dead skin cells inside the pore. For that reason, BHAs are especially useful for people with acne-prone or oily skin. By helping to unclog pores and reduce oil buildup, they can play an important role in preventing blackheads, whiteheads, and inflammatory breakouts. BHAs also have mild anti-inflammatory properties, which is another reason they are commonly used in acne-focused skincare formulations. BHAs are also generally considered milder than AHAs in terms of surface irritation, since their larger molecular weight means that they do not penetrate as aggressively at the skin surface level. Chemical peels are essentially a concentrated application of these same acids. AHAs, BHAs, or sometimes a combination. They're delivered at higher concentrations and lower pH levels than you use in everyday skincare products. The lower the pH and the higher the concentration, the deeper and more significant the exfoliation. At-home chemical peel products are formulated to be effective but safe for regular self-use, while professional in-office peels use higher concentrations that can achieve more dramatic results with a single treatment. There is also a third category worth knowing about, which are PHAs, or polyhydroxy acids. PHAs work similarly to AHAs but have a larger molecular size, meaning that they penetrate more slowly and gently. This makes them an excellent option for sensitive skin types who may find traditional AHAs too irritating. Most people can use PHA-based products without significant side effects. So how do you know which one is right for you? If your primary concerns are fine lines, uneven skin tone, dark spots, dullness, or surface texture, an AHA is likely your best starting point. If you struggle with acne, clogged pores, blackheads, or excess oil, a BHA like salicylic acid is going to be more targeted and effective. Now, if you have sensitive skin and want the benefits of chemical exfoliation with less risk of irritation, a PHA may be the gentlest place to begin. And can you use both AHAs and BHAs together? Research does suggest they can complement each other. And some products do combine them. However, because both are exfoliants, using them together in the same routine can increase the risk of irritation and dryness. A better approach is often to alternate. You might use one in the morning and the other at night, or use each on different days, rather than layering them on top of one another at the same time. One rule that applies no matter which exfoliant you choose is daily sunscreen. Both AHAs and BHAs increase your skin's sensitivity to UV light, which means skipping sunscreen while using these ingredients significantly raises your risk of sun damage. Applying a broad-spectrum SPF every morning helps protect your skin and allows you to get the benefits of exfoliation without undoing the progress that you're trying to make.
