Polyhydroxy Acids (PHA)

Gentle, multi-weight exfoliants that dissolve dead skin without irritation.

Also known as: Polyhydroxy Acids, gluconolactone, galactose, lactobionic acid, INCI: Gluconolactone, Galactose, Lactobionic Acid.

What it is

PHAs are a class of chemical exfoliants with larger molecular weight than AHAs and BHAs, derived from sugars (gluconolactone) or sugar derivatives (lactobionic acid, galactose). Their size limits penetration to the skin surface, making them gentler than traditional hydroxy acids.

What it does

PHAs dissolve the bonds between dead skin cells, promoting gentle exfoliation and cell turnover. They also have humectant properties, drawing moisture into the skin, and may offer mild antioxidant and anti-inflammatory benefits. Unlike AHAs and BHAs, their larger molecular weight reduces irritation and sun sensitivity while still improving texture, radiance, and skin clarity.

The evidence

Moderate evidence supports PHA efficacy for gentle exfoliation and skin texture improvement, particularly in sensitive skin. Studies show they are less irritating than AHAs at equivalent concentrations, though fewer large-scale clinical trials exist compared to AHAs/BHAs. Evidence for anti-inflammatory and humectant benefits is emerging.

Best for

Sensitive, reactive, or compromised skin; those intolerant of AHAs or BHAs; post-procedure skin; and anyone seeking gentle, consistent exfoliation without irritation.

Pairs well with

Niacinamide, ceramides, hyaluronic acid, peptides, and gentle hydrating serums. Safe to layer with retinoids at lower frequencies. Works well in combination with other PHAs.

Use cautiously with

Use cautiously with vitamin C (L-ascorbic acid) at low pH, as pH competition may reduce efficacy of both. Avoid combining with high-dose AHAs or BHAs on the same day to prevent over-exfoliation.

Cautions

Generally well-tolerated; rare irritation in very sensitive skin. No significant photosensitivity, but sunscreen is still recommended post-exfoliation. Safe in pregnancy; not prescription-only.