Which exfoliant to choose: AHA, BHA, or PHA for your skin?

Glycolic, lactic, salicylic, polyhydroxy: behind these names lies a single promise – to remove dead skin cells to reveal clearer, brighter skin. But not all these acids are equal, and crucially, they don't suit the same skin types.

When chosen correctly, a chemical exfoliant refines skin texture, unclogs pores, and evens out skin tone without any harsh scrubbing. When chosen poorly, it can weaken the skin barrier, leading to redness and sensitivity. Here's how to decide, from a pharmacist's perspective.

Exfoliating isn't about stripping the skin: it's about gently helping the skin do what it already knows how to do.

Three families of acids, three approaches to penetration

AHAs (alpha-hydroxy acids), like glycolic acid and lactic acid, are water-soluble. They work on the surface by loosening the cohesion between corneocytes, the cells of the stratum corneum, which promotes uniform desquamation without disrupting the barrier. Glycolic acid is the smallest molecule in this family: it penetrates quickly and deeply, making it effective but more irritating. Lactic acid, being larger, acts more gently and also has a hydrating effect.

BHA primarily refers to salicylic acid. Being oil-soluble, it penetrates into the sebum and cleanses the inside of the pore: it's the acid for oily and blemish-prone skin, with well-documented keratolytic and comedolytic actions. Finally, PHAs (polyhydroxy acids, like gluconolactone) are even larger molecules that remain on the surface, making them particularly gentle.

Which acid for which skin type

For dull, marked, or dehydrated skin, AHAs are recommended: lactic acid to start or for dry skin, glycolic acid when the skin already tolerates active ingredients well and you're aiming for radiance and smoothness. For oily, combination, or skin prone to enlarged pores and blackheads, salicylic acid remains the gold standard, as it alone works inside the follicle.

For sensitive, reactive, or redness-prone skin, PHAs are the best entry point: gluconolactone exfoliates without the tingling sensation of AHAs, and it has the added benefit of not increasing the skin's sensitivity to the sun, unlike AHAs.

Frequency, or the art of not overdoing it

The rule is simple: start gently and space out applications. A mild exfoliant (PHA, low percentage AHA) can be used two to three times a week; for a more potent acid, once or twice a week is ample. Skin needs several days to rebuild its surface lipids between applications.

There's no need to combine exfoliants: using a salicylic acid cleanser, a glycolic toner, and an AHA serum consecutively is a sure path to over-exfoliation. It's better to choose one well-suited acid and use it at the right frequency.

Recognizing signs of over-exfoliation

When you exceed the dose your skin tolerates, you damage the skin barrier: you remove the lipids that retain water, which increases transepidermal water loss and triggers inflammation and discomfort. Warning signs are recognizable: tightness, a burning sensation even with basic products, redness, flaking, paradoxical shininess of otherwise dehydrated skin, and even breakouts.

If these signs appear, suspend all acids, switch back to a gentle cleanser, a restorative treatment rich in ceramides, and sunscreen, allowing the barrier to rebuild – often two to four weeks.

Photosensitivity and SPF, the non-negotiable habit

AHAs increase skin's sensitivity to the sun and the risk of sunburn; this increased sensitivity persists for up to a week after discontinuing the product, which is why health authorities recommend daily sunscreen use during and after an AHA regimen. BHA is less of a concern, and PHAs do not cause photosensitivity. But regardless of the acid family, exfoliating without SPF is like undoing with one hand what you build with the other. It's best to exfoliate in the evening and apply SPF 50 every morning.

The Paradermia approach

Our conviction as pharmacists: a single acid, carefully chosen for your skin, used at the correct frequency, yields better results than an accumulation of products. We favor a gradual increase in potency—starting with a PHA or lactic acid, observing tolerance, then adjusting—rather than the promise of immediate radiance that often comes at the cost of sensitivity. And always, SPF as a safeguard. This logic of a personalized routine, adapted to your skin type rather than a trend, is what we advocate.

Frequently Asked Questions

Can AHA and BHA be used simultaneously?
Yes, but rarely on the same night and only if the skin is tolerant. The safest approach is to alternate nights, or to reserve BHA for oily areas and AHA for the rest of the face, to avoid over-exfoliation.

Are PHAs truly effective or just gentler?
They do exfoliate, but more slowly and on the surface compared to AHAs. Their benefit is allowing exfoliation for sensitive skin that tolerates neither glycolic nor salicylic acid, without tingling or photosensitization.

How often should you exfoliate when starting out?
Once a week for two to three weeks to assess tolerance, then gradually increase if the skin remains comfortable. At the slightest sign of tightness or redness, reduce frequency.