AHA · BHA
The Two Pillars of Exfoliation

Updated 2026 · By the Beauty Dupe editorial team

Shop for an exfoliant and you will run into AHA and BHA almost right away. Both loosen dead skin with acid instead of scrubbing it off (chemical exfoliation). The real difference is how deep they go. AHA (alpha hydroxy acid) works on the very top of your skin while BHA (beta hydroxy acid) travels down into the pore. So once you know whether your problem sits on the surface or inside your pores, the choice gets a lot easier.

At a glance

AHA vs BHA: side by side

Dealing with both? Some products put AHA and BHA in the same bottle. We counted the 2,426 full ingredient lists in our database. AHA (glycolic, lactic or mandelic acid) showed up in 147 of them and salicylic acid in 117, and 33 products had both. Keep in mind that an ingredient list never shows strength. A name on the list does not mean there is enough to exfoliate, so check the percentage on the product page too.

AHA: the main types and how they differ

There are several AHAs, but one rule covers them all. The smaller the molecule, the deeper it goes and the faster it works, and the more it stings.

Glycolic acid

Glycolic acid is known to come from sugar cane, and at a molecular weight of 76 it is the smallest AHA. It sinks in easily and shows results fast, though it also stings the most. Most products use 5 to 10%. Anything above 30% belongs in the hands of a skin professional. On a label, look for Glycolic Acid.

Lactic acid

Lactic acid has a molecular weight of 90. That slightly larger size makes it gentler than glycolic, and it also holds water in the skin as it exfoliates. So it is a good first AHA for dry or sensitive skin or for anyone new to acids. You will find plenty of products at 5 to 10%.

Mandelic acid

Mandelic acid is known to come from almonds and has a molecular weight of 152. As the largest of the three, it works the slowest and the most gently. People use it for pigmentation and acne marks, and reactive skin usually tolerates it well. Citric acid is an AHA too, though in skincare it mostly shows up to adjust pH.

BHA: almost always salicylic acid

In skincare, BHA nearly always means salicylic acid, listed as Salicylic Acid on the label. It is oil-soluble, so it mixes into sebum and slips inside the pore. Once there, it dissolves the trapped oil and dead skin. Products sold abroad usually use 0.5 to 2%, while Korea caps leave-on cosmetics at 0.5%.

That makes it a strong pick when clogged pores are the problem, like the blackheads and tiny bumps that cluster on the nose and chin. It belongs to the same family as aspirin and calms inflammation, so it also helps settle red, angry spots. We cover the rinse-off limits and how to read the label in our AHA, BHA and PHA concentration guide.

How do AHA and BHA actually work in the skin?

Dead skin cells are held together by a kind of protein glue. Acids loosen that glue so worn-out cells drop off on time, all on their own. You never have to rub your skin the way you would with a grainy scrub.

The difference is the route. AHA dissolves in water and stays on the surface, while BHA dissolves in oil and travels down into pores full of sebum. That is why the same job calls for a different acid depending on your concern.

How to use it by strength

Think of strength as a ladder. Start on a low rung and move up one step once your skin is used to it.

AHA

• 2–5%: the starting point if you are new to acids or have sensitive skin.
• 5–10%: the most common, standard range. Move here once a lower strength feels easy.
• 10–20%: for people who have used acids for a while, and only at night.

BHA

• 0.5%: the cap for Korean leave-on products and an easy entry point for sensitive skin.
• 1–2%: common in products sold abroad. If you buy overseas, know that you are picking the stronger option.
• 2% and up: found in products sold abroad and in peels, for short bursts of focused care.

How often to apply it, and how to build up over the first weeks, is laid out step by step in our beginner concentration and routine guide.

Side effects and precautions

• AHA makes you more sun-sensitive. In one study, skin treated with 10% glycolic acid reddened more easily under UV and showed more signs of damage. In the same study, 2% salicylic acid made no clear difference. Wear SPF 30 or higher during the day with either one, and keep AHA to nights at first.
• The first 2 to 4 weeks are a break-in phase. Some tingling or light flaking is common. Use it less often and let your skin catch up.
• Keep retinol on separate nights. Both can irritate, and stacking them on the same night adds up.
• Check the BHA strength in pregnancy. Low-strength topical use (2% or under) is generally considered fine. High-strength peels or long use over a wide area are best avoided. AHA tends to be the easier choice.
• Take a break right after lasers or peels. Give your skin a week or two to recover before you start again.

What to pair it with, and what to watch

Frequently asked questions