BHA vs AHA: What’s the Difference, and Which One Do You Need?

Two initialisms, one shelf, no explanation. AHA and BHA turn up on exfoliant labels as though everyone already knows the difference — and the products either side of them look practically identical.

The distinction is actually simple, and it comes down to one property: AHAs dissolve in water, BHA dissolves in oil. Everything useful follows from that. And there's a second difference, less widely known but arguably more important in a year-round-sun climate, which we'll come to.

Short answer: AHAs dissolve in water and work across the skin's surface; BHA dissolves in oil and can reach inside pores. Surface texture and tone point towards an AHA; congestion and surface oil point towards BHA. Most skin benefits from a bit of both.

The core difference: where each one can go

AHAs — glycolic, lactic, mandelic — are water-soluble. They work across the skin's surface, loosening the bonds between dead cells so they shed more evenly.

BHA — in practice, salicylic acid — is oil-soluble. Unlike glycolic acid, it mixes with the skin's own surface oils and with the oil sitting inside hair follicles.[1] Water-based ingredients simply can't follow it there.

Both loosen the connections holding dead cells at the surface. Salicylic acid does it by unglueing those connections rather than dissolving the keratin proteins inside the cells,[1] and it acts on the stratum corneum — the outermost layer you can actually touch.[1]

So: surface texture and tone → AHA territory. Congested follicles and surface oil → BHA territory. Most people's skin has some of both, which is why blends exist.

The sun difference nobody mentions

This is the one worth knowing, and in Singapore it's not academic.

AHAs measurably increase sun sensitivity. The FDA's own research found sensitivity to UV-induced reddening rose 18% after four weeks of AHA application.[2] The effect is reversible — it resolves within about a week of stopping[2] — but it's real enough that the FDA recommends AHA cosmetics carry a specific sunburn alert, advising sun protection during use and for a week afterwards.[2]

Salicylic acid is assessed differently. The Cosmetic Ingredient Review panel removed its sun-sensitivity qualification for salicylic acid, after a national toxicology study found salicylic acid creams were mildly photoprotective.[3] Its current conclusion carries no sun-sensitivity caveat.[3]

That's a genuine, documented difference between the two families — not a marketing distinction. It doesn't make AHAs unsuitable; it makes daily sunscreen non-negotiable alongside them. Which, at this latitude, it is anyway.

Strength isn't the percentage alone

A common mistake is comparing two products by their percentages.

The FDA is explicit that how much exfoliation an AHA product delivers depends on the acid type, its concentration, the product's pH, and the rest of the formulation — not concentration alone.[2] For consumer AHA products, the CIR panel's safety conditions are three things at once: 10% or less, pH 3.5 or greater, and formulated to protect against increased sun sensitivity.[2]

The same holds for salicylic acid, where format drives everything: rinse-off products have been reported as high as 30% — that's a peel — while the maximum in any leave-on cosmetic is 2%.[3]

It's also worth knowing that the FDA attributes the more serious AHA adverse reactions specifically to high-exfoliation products such as skin peelers, distinguishing them from ordinary cosmetic AHA products.[2] The scary stories mostly aren't about the category you're shopping in.

So which do you need?

If your main concern is…	Lean towards
Rough, uneven surface texture	AHA
Dull, patchy-looking tone	AHA
Congestion, visible pores, surface oil	BHA
Bumpy texture around follicles	BHA
Sensitive skin	Larger, slower acids — and see below
A bit of everything	A blend

The honest answer for most people is both, which is why multi-acid formulas exist — different acids reach different depths and address different problems, at low individual doses.

Where the Cetaphil SA range sits

The Cetaphil Gentle Exfoliating SA Cleanser and Cetaphil Gentle Exfoliation SA Lotion use a blend rather than asking you to choose — clinically proven gentle chemical exfoliation that smooths the appearance of skin texture, visibly evens tone and brightens overall appearance, while preserving the skin's barrier.

Both are suitable for sensitive skin, gentle enough for everyday use, and clinically tested for all skin tones and types. The cleanser improves skin barrier protection for up to 8 hours after a single application.[4] The lotion is suitable for face and body.

Whichever you use, wear sunscreen daily — that advice holds for every exfoliating acid, and in Singapore it holds regardless.

Frequently asked questions

Can I use an AHA and a BHA together?
In a formulated blend, yes — that's what multi-acid products are. Layering two separate strong products yourself is where people get into trouble.

Which is gentler?
Neither family wins outright; it depends on the specific acid and the formulation. Within the AHAs, larger and slower-absorbing ones are better tolerated than small fast ones. Salicylic acid at everyday concentrations is also mildly anti-inflammatory.[1]

Do I really need sunscreen with these?
With AHAs, the evidence is specific — an 18% rise in UV sensitivity after four weeks, reversing about a week after stopping.[2] With salicylic acid the picture differs.[3] But in this climate daily sunscreen is the baseline either way.

Is BHA only for oily skin?
No. Its oil-solubility makes it useful for congestion, but salicylic acid is documented as well tolerated across every Fitzpatrick skin type from I to VI.[1]

What about PHAs?
A third family — larger molecules again, generally the gentlest of the three, and often included in blends for exactly that reason.

The takeaway

AHAs are water-soluble and work across the surface; BHA is oil-soluble and can reach inside follicles. That single property drives which suits which concern. The less-known difference is sun sensitivity: AHAs measurably increase it, while salicylic acid's sun qualification was withdrawn on the evidence. Most skin benefits from a bit of both, at low doses, used consistently — with sunscreen either way. If your skin stays irritated or a concern persists, see a doctor or dermatologist.

Product information: Cetaphil Gentle Exfoliating SA Cleanser · Cetaphil Gentle Exfoliation SA Lotion