AHA (alpha hydroxy acid) and BHA (beta hydroxy acid) are the two acids behind chemical exfoliation, the approach that dissolves dead skin instead of scrubbing it off. Both loosen the buildup that dulls your complexion and leave the surface smoother. Where they part ways is depth. AHA does its work right on the surface while BHA travels down into the pore.
The short version AHA is water-soluble, so it suits surface flaking along with dryness and uneven tone. BHA is oil-soluble, which lets it clear the breakouts and blackheads sitting inside your pores. Both make skin more sensitive to sunlight, so sunscreen during the day is not optional.
Exfoliation, pores, breakouts, brightening, fine lines
AHA vs BHA — side by side
AHA
Alpha hydroxy acid
Type: Water-soluble
Where it works: Skin surface
Best suited to:
Dry or combination skin
Thick, built-up texture
Dark spots and pigmentation
Fine lines and aging
BHA
Beta hydroxy acid
Type: Oil-soluble
Where it works: Inside the pore
Best suited to:
Oily or breakout-prone skin
Blackheads and whiteheads
Large pores
Body breakouts on the back and chest
AHA — the main types and how they differ
Glycolic acid
Its molecules are the smallest of the group, so it sinks in easily. You feel the results fast, though that speed comes with a sharper sting. Most products land somewhere between 5 and 10%, and anything above 30% belongs in the hands of a skin professional.
Lactic acid
Lactic acid has a larger molecule than glycolic, which makes it gentler on the skin. It hydrates as it exfoliates, and that makes it a good match for sensitive skin or anyone trying acids for the first time. Look for it around 5 to 10%.
Mandelic acid
With the largest molecule of the three, mandelic is the mildest and least irritating. It helps with pigmentation and acne scarring while staying comfortable on reactive skin.
BHA — almost always salicylic acid
In skincare, BHA nearly always means salicylic acid. It usually shows up at 0.5 to 2%. Because it is oil-soluble, it dissolves the sebum, debris and dead skin packed deep inside a pore.
That makes it a strong pick for breakout-prone skin, especially the whiteheads and blackheads that cluster on the nose and chin. It also calms inflammation, so it helps soothe irritated, congested areas.
How do AHA and BHA actually work in the skin?
Dead skin cells hold onto each other through tiny protein links (corneodesmosomes). These acids cut those links so the old buildup sheds on its own. Unlike a grainy scrub, there is no rubbing involved. The skin simply gets back to turning itself over on schedule.
AHA stays up on the surface because it is water-soluble, while BHA is oil-soluble and slips down into pores filled with sebum. Same job, two different routes in. That difference in depth is the whole reason you reach for one over the other.
How to use it by strength
AHA
2–5%: a good starting point for beginners and sensitive skin. Fine for daily use.
5–10%: the standard range. Start at 3 to 5 times a week, then move to daily once your skin adjusts.
10–20%: for experienced users. Use 2 to 3 nights a week, and only at night.
BHA
0.5%: an entry-level strength for sensitive skin. Fine for daily use.
1–2%: the standard range. Use nightly or every other night.
2% and up: for short bursts of focused care. About 2 to 3 times a week is plenty.
Side effects and precautions
Sun sensitivity. These acids leave skin more vulnerable to sunlight, which can lead to pigmentation or redness. Pair daytime use with an SPF 30 or higher sunscreen, and stick to nights at first.
A break-in phase. Some tingling or flaking is common in the first 2 to 4 weeks. Dial back how often you use it and let your skin catch up.
Space them out from retinol. Both can irritate, so skip using them on the same night. Alternate them day by day instead.
Be careful with BHA in pregnancy. Salicylic acid is in the same family as aspirin, so it is safest to avoid during pregnancy. AHA is the more comfortable choice.
Hold off right after lasers or peels. Give your skin a week or two to recover before you start again.
You can. Just keep in mind that running both at once turns up the irritation, so start with low strengths (AHA 2–5%, BHA 0.5–1%). A toner that already blends AHA and BHA is an easy way to ease in.
My skin tingles. Is that a side effect?
A little tingling during the first 2 to 4 weeks is pretty normal. If the sting is strong and lasts more than half an hour, or your skin turns red and puffy, drop the strength or use it less often.
Can I use it in the morning?
You can, but it is not the best idea because these acids make skin more sun-sensitive. If you do use them in the morning, layer on a generous SPF 30 or higher. Night is the better window.
Can I use it with retinol?
Not at the same time. Alternate them day by day instead. You might do AHA or BHA on Monday, Wednesday and Friday, retinol on Tuesday, Thursday and Saturday, then rest on Sunday.
Is it safe during pregnancy?
AHA is generally fine to keep using through pregnancy. BHA (salicylic acid) sits in the same family as aspirin, so it is safest to skip while pregnant. Check with your doctor before you start.
When will I see results?
Texture and smoothness tend to show in 2 to 4 weeks, pores and blackheads in 4 to 8 weeks, and fine lines or pigmentation from 12 weeks onward.
