AHA vs BHA
AHA vs BHA — two families of chemical exfoliants distinguished by how they interact with skin, with alpha hydroxy acids (AHAs) being water-soluble and working on the surface to smooth texture and tone, while beta hydroxy acids (BHAs) are oil-soluble and can penetrate into pores. The choice often comes down to whether concerns are surface-level or related to congestion and oil.
Key points
- AHAs such as glycolic and lactic acid are water-soluble and target surface texture, dullness, and uneven tone.
- BHAs, most commonly salicylic acid, are oil-soluble and can work inside pores, making them well suited to congestion and oily skin.
- AHAs are often favored for dry or sun-affected skin, while BHAs are popular for blemish-prone and combination skin.
- Both increase sun sensitivity, so daily sunscreen is especially important when using either type of acid.
AHA vs BHA at a glance
| AHA | BHA | |
|---|---|---|
| Solubility | Water-soluble | Oil-soluble |
| Where it acts | On the skin surface | At the surface and inside the pore |
| Best-known members | Glycolic, lactic, mandelic acid | Salicylic acid; willow bark |
| Typical strengths | 5–10% leave-on | 0.5–2% leave-on |
| Best at | Dullness, rough texture, uneven tone, fine lines | Blackheads, congestion, visible pores, oiliness |
| Who it suits | Normal, dry, mature or sun-affected skin | Oily, combination, blemish-prone skin |
| Irritation profile | Stinging and flaking if overused | Dryness more than stinging; mildly calming |
| Sun sensitivity | Clearly increased; daily sunscreen needed | Increased, though less established; sunscreen advised |
How each one works
AHAs are small organic acids that weaken the bonds holding dead cells to the skin surface, so those cells shed more readily than they would alone. Being water-soluble, they stay in the watery environment at the surface and act broadly across it, which is why they change overall texture and tone rather than target one spot.
Salicylic acid, the main BHA, is oil-soluble, so it mixes with sebum and travels into the pore lining, where it loosens the plug of oil and dead cells that forms blackheads and closed comedones. It is also related to aspirin and has a mild calming effect on redness around a blemish.
Which to choose
The useful question is where the problem sits. Surface concerns — dullness, roughness, uneven tone, sun-related pigmentation, fine lines — point to an AHA. Concerns inside the pore — blackheads, congestion, an oily T-zone, recurring blemishes — point to a BHA.
Skin type narrows it further. Dry, mature or sun-affected skin tends to prefer AHAs, with lactic acid gentler than glycolic. Oily and combination skin usually tolerates BHA well, and low-strength salicylic acid is often manageable on redness-prone skin. Painful or scarring acne warrants a clinician rather than a stronger acid.
Using them together, or switching
They can be used together, and some formulas combine them, but the cost is cumulative irritation. Alternating nights is more forgiving, as is splitting by area — BHA on congested zones, AHA elsewhere. A rinse-off BHA cleanser alongside a leave-on AHA also reduces the overlap.
If you are switching, change one thing at a time and give the new acid four to six weeks before judging it. Start at two nights a week and build. Tightness, stinging when moisturiser goes on, or new sensitivity means you are exfoliating too much, whichever acid you use.
Frequently asked
What is the main difference between AHA and BHA?
AHAs are water-soluble and exfoliate the skin surface, while BHAs are oil-soluble and can reach into pores, making BHAs better suited to oil and congestion.
Can I use AHA and BHA together?
They can be combined or alternated, but doing both at once may increase irritation, so many people introduce them gradually and pair them with sunscreen.
Can I use a BHA if my skin is dry?
Yes, though it may feel drying at first. A low strength two or three times a week, followed by a moisturiser, is usually tolerated. If texture rather than congestion is the concern, an AHA suits better.
Which one goes on first if I use both in the same routine?
Apply the thinner, more fluid product first, usually the BHA, and give it a minute before the AHA. If either is a rinse-off product, use it at the cleansing step instead.
Do I need a high percentage for an acid to work?
No. Most leave-on AHAs work at 5 to 10 per cent and BHAs at 0.5 to 2 per cent, and formulation and pH matter as much as the number. Higher strengths mainly raise irritation.
How long before I see a difference?
Surface smoothness often shifts within two to four weeks. Congestion and uneven tone generally take eight to twelve weeks. If nothing has changed after three months, the acid is probably not right for that concern.
Related topics
This is a foundational entry in the SYNC Skin Encyclopedia and is expanded over time. Educational information only — not medical advice.
