Polyhydroxy acid

The short answer

Polyhydroxy acid, usually shortened to PHA, means a family of skincare acids used for gentle surface exfoliation and hydration-supportive smoothing.

Gluconolactone and lactobionic acid are common examples.

What the term means on a label

PHA tells you the acid family, not the whole behaviour of the product.

A review of polyhydroxy acids^[1] describes PHAs such as gluconolactone and lactobionic acid as ingredients with smoothing, humectant, moisturising, and antioxidant properties. It also discusses their use in photoaged and sensitive-skin contexts.

That does not mean every PHA product is automatically gentle. Concentration, pH, product type, and frequency still matter.

PHA vs AHA vs BHA

Use the terms like this:

• AHA: water-soluble acids such as glycolic acid, lactic acid, and mandelic acid, often used for surface texture and tone.
• BHA: usually salicylic acid, oil-soluble and more useful for blackheads, oily follicles, and clogged pores.
• PHA: acids such as gluconolactone, often used when the goal is milder-feeling surface smoothing.

If your label says PHA, think "gentle texture support" before you think "deep pore unclogger."

What to do with the term

The American Academy of Dermatology says exfoliation can improve appearance for some people, but it is not for everyone and can cause harm when done improperly^[2]. That warning still applies to PHA.

Use PHA calmly:

• start once or twice weekly
• avoid stacking it with retinol at first
• moisturise after
• use SPF in the morning
• stop if skin becomes tight, burning, or flaky

For a fuller routine, read the guide to dull-looking skin. If your skin already stings from actives, start with barrier repair instead.

Mads's practical read

PHA is a useful label word when your skin wants smoother texture but dislikes aggressive acids.

Still, do not collect acid categories like trading cards. Pick the one that matches the job, use it slowly, and let your skin vote with comfort.