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AHA, BHA, and PHA Exfoliating Acids Explained

AHA, BHA, and PHA all exfoliate by loosening the bonds between dead skin cells, but they differ in solubility, depth of action, and how gentle they feel on skin.

AHA: water-soluble, works on the surface

Alpha hydroxy acids like glycolic acid and lactic acid dissolve in water and work primarily on the skin's surface, loosening the bonds between dead skin cells to reveal smoother, brighter skin underneath. Glycolic acid has the smallest molecule of the common AHAs and penetrates most readily.

BHA: oil-soluble, gets inside pores

Salicylic acid is the main beta hydroxy acid used in skincare, and its oil solubility lets it penetrate into sebum-filled pores rather than just working on the surface, which is why it is the go-to exfoliant for blackheads, clogged pores, and acne-prone skin.

PHA: larger molecules, gentler on sensitive skin

Polyhydroxy acids like gluconolactone and lactobionic acid work similarly to AHAs but have larger molecules that penetrate more slowly, making them a common recommendation for sensitive, reactive, or rosacea-prone skin that reacts poorly to stronger AHAs.

Matching the acid to your main concern

Dry or sun-damaged skin generally responds well to AHAs for texture and brightness; oily or acne-prone skin usually benefits more from BHA for pore congestion; sensitive or easily irritated skin often tolerates PHA best while still getting some exfoliating benefit.

Layering acids and sun sensitivity both need care

Using multiple strong acids together, or combining them with retinoids, raises the risk of irritation, so many routines alternate rather than stack. All chemical exfoliants increase sun sensitivity, making daily sunscreen non-negotiable while using them.

Why solubility determines where an acid actually works

Pores are filled with oil, not water, which is exactly why an oil-soluble acid like salicylic acid can travel inside a pore while a water-soluble AHA largely stays on the skin's surface. This single chemical property explains most of the practical difference in what each acid is good for, more than concentration alone does.

Why starting slow matters more than picking the "best" acid

Introducing any new acid gradually β€” a few nights a week before daily use, patch-tested first β€” lets skin build tolerance and reveals irritation early before it becomes a widespread reaction. Reaching for the strongest formulation immediately is a common reason people give up on chemical exfoliants after a bad first experience.

Frequently Asked Questions

Can I use an AHA and a BHA on the same day?

Many people do, often in formulas that combine both, but sensitive skin generally tolerates alternating them on different days better than stacking both at full strength in one routine, at least until tolerance is established.

Do chemical exfoliants really increase sun sensitivity?

Yes, meaningfully. Removing the outer layer of dead skin cells reduces some of skin's natural sun protection, so daily broad-spectrum sunscreen is considered essential, not optional, whenever any AHA, BHA, or PHA is part of a routine.