AHAs, BHAs, and How They Work

Chemical exfoliants work by loosening the bonds between dead skin cells rather than physically scrubbing them away. They're categorized into AHAs (alpha-hydroxy acids) and BHAs (beta-hydroxy acids), and they work differently.

AHAs — surface exfoliation

AHAs are water-soluble and work primarily on the skin's surface. They're effective for evening texture, brightening dull skin, and fading hyperpigmentation. Common AHAs: glycolic acid (strongest, smallest molecule), lactic acid (gentler, also hydrating), and mandelic acid (gentlest).

BHAs — deep pore exfoliation

BHAs are oil-soluble, which means they can travel into the sebum-filled pores. Salicylic acid is the primary BHA used in skincare. It's anti-inflammatory and particularly effective for oily, acne-prone skin. It loosens clogs from inside the pore, which is something AHAs cannot do.

PHAs — the gentle option

PHAs (polyhydroxy acids) like gluconolactone have a larger molecule size, which means they work even more slowly and gently. They're often recommended for sensitive skin or for people who react to AHAs.

How often to exfoliate

For most people, 1–3 times per week is sufficient. Over-exfoliation is common and recognizable: skin feels tight, shiny, stingy when you apply toner, and may look raw or red. If this happens, stop all exfoliants, use a barrier-supporting routine, and let skin recover for 1–2 weeks.

What the evidence says

The exfoliating and skin-renewing effects of alpha- and beta-hydroxy acids are well documented in the dermatology literature (see Kornhauser et al., Clinical, Cosmetic and Investigational Dermatology, 2010), including glycolic and lactic acid for texture and tone and salicylic acid for acne. The same literature is clear that benefit is dose- and frequency-dependent — and that over-use compromises the barrier — which is why "less, but consistent" is the evidence-based approach.

This article is general educational information, not medical advice. Skincare needs vary from person to person. Always patch-test new products and consult a qualified professional (such as a dermatologist) for persistent or serious skin concerns.