AHA vs BHA vs PHA: Exfoliant Guide
Understanding Chemical Exfoliation
Chemical exfoliants dissolve the desmosomes (protein bonds) between dead skin cells, promoting cell turnover without physical abrasion. The three main categories differ in molecular size, penetration depth, and mechanism.
AHA (Alpha Hydroxy Acids)
Molecules: Glycolic acid (smallest: 76 Da), lactic acid (90 Da), mandelic acid (152 Da), tartaric acid.
Penetration: Water-soluble, works on skin surface and upper epidermis. Smaller molecules penetrate deeper. Glycolic penetrates deepest (most effective, most irritating). Mandelic is gentlest.
Best for: Surface exfoliation, hyperpigmentation, fine lines, dullness. Not ideal for acne (doesn't penetrate oil-filled pores).
Safe frequency: 5-10% concentration, 2-3x weekly. Higher concentrations (20%+) should only be used as professional peels.
BHA (Beta Hydroxy Acid)
Molecule: Salicylic acid (138 Da). Oil-soluble, which is the critical difference.
Penetration: Penetrates into oil-filled pores and follicles. Dissolves sebum and dead cells within the pore. Also has anti-inflammatory properties (aspirin derivative).
Best for: Acne, blackheads, enlarged pores, oily skin. Less effective for surface pigmentation.
Safe frequency: 1-2% concentration, daily to 2x daily for acne treatment. 2% BHA liquid is the gold standard for pore-clearing.
PHA (Polyhydroxy Acids)
Molecules: Gluconolactone (178 Da), lactobionic acid (358 Da). Much larger molecules.
Penetration: Stay on the surface. Provide gentle exfoliation plus humectant properties. Also have antioxidant capacity.
Best for: Sensitive skin, rosacea, beginners, barrier-compromised skin. Can be used daily without irritation.
The Right Choice for Your Skin
Oily/acne-prone: 2% BHA. Dull/pigmented/aging: 8-10% glycolic or lactic acid. Sensitive/rosacea: PHA (gluconolactone). Combination: alternate BHA (pores) and AHA (surface) on different nights. Never combine all three in the same routine.
