AHA, BHA & PHA — Exfoliating Acids
Three categories of chemical exfoliant, each with a distinct mechanism
Function in skin biology
Exfoliating acids work by loosening the bonds between dead skin cells on the surface of the stratum corneum, encouraging more even shedding than mechanical (scrub-based) exfoliation. The three major categories differ in molecular size, solubility and where in the skin they act:
- AHAs (alpha-hydroxy acids) — water-soluble, act primarily on the skin surface. Common examples: glycolic acid, lactic acid, mandelic acid.
- BHA (beta-hydroxy acid) — oil-soluble, able to penetrate into the pore lining. The primary cosmetic BHA is salicylic acid.
- PHAs (polyhydroxy acids) — larger molecules than AHAs, penetrating more slowly and generally associated with a gentler tolerability profile. Common examples: gluconolactone, lactobionic acid.
Why Ambernay evaluates this category
Exfoliating acids are evaluated case by case for tolerability, concentration and pH — factors that determine both efficacy and irritation potential more than the acid type alone. PHAs are generally considered for sensitive-skin contexts, BHA for formulas targeting visible pore appearance and surface texture, and AHAs for general surface renewal.
Where concentration matters
Cosmetic AHA formulas are typically below 10% with a finished product pH above 3.5 (higher concentrations and lower pH are regulated more strictly and associated with higher irritation potential). Salicylic acid (BHA) is commonly formulated between 0.5% and 2%. PHAs are often formulated at higher percentages than AHAs due to their gentler profile and larger molecular size.
What we do not claim
We do not claim that any exfoliating acid treats acne as a diagnosed condition, removes "toxins," or produces permanent structural skin change. Exfoliating acids are evaluated for their visible texture and surface-renewal contribution within a cosmetic context.
Best paired with
Exfoliating acids increase photosensitivity — daytime SPF is essential when any of these are part of a routine. They are generally not combined with retinoids in the same routine step to avoid over-exfoliation, and benefit from being paired with barrier-supportive moisturisers.
Claim caution / regulatory note
AHA, BHA and PHA ingredients are regulated cosmetic actives with concentration and pH limits in most markets (e.g., EU Annex III restrictions on certain AHAs). Claims must remain within cosmetic function: surface texture, visible smoothness, pore appearance. Acne treatment claims require drug-level substantiation and regulatory status.