If every exfoliating acid you've tried has left your face red and stinging, PHAs were made for you. Polyhydroxy acids are the third, least famous family of exfoliating acids after AHAs and BHA, and their whole selling point is doing the same job with a fraction of the irritation.
What is a polyhydroxy acid?
PHAs are chemical exfoliants, and the names to look for on labels are gluconolactone, lactobionic acid and galactose. Structurally they're close cousins of AHAs, with one crucial difference: the molecules are much larger. A bigger molecule can't sink into the skin as quickly or as deeply, so PHAs work almost entirely on the surface, loosening the bonds that hold dead skin cells in place so they shed evenly.
Slower and shallower sounds like a downgrade, but for exfoliation it's precisely what makes PHAs so well tolerated. Most of the sting from glycolic acid comes from how fast it penetrates. PHAs take the scenic route, and your skin barely notices the work being done.
What PHAs do for your skin
Gentle exfoliation. The headline benefit. PHAs smooth rough texture, soften the look of fine lines and gradually brighten dull skin the same way AHAs do, just more slowly and with far less risk of redness. They're regularly recommended for people with sensitive skin, rosacea-prone skin and eczema-prone skin who can't tolerate traditional acids.
Hydration while they exfoliate. This is PHAs' genuine party trick. Gluconolactone and lactobionic acid are humectants, meaning they attract and hold water in the skin. Most acids leave your skin drier; PHAs leave it better hydrated than they found it, which also makes them kinder to your skin barrier.
Antioxidant activity. PHAs have measurable antioxidant properties, helping neutralise some of the free radical damage that drives premature aging. It's a supporting benefit rather than a headline one, but no other exfoliant family offers it.
A brighter, more even tone. By keeping dead cell turnover ticking along, PHAs gradually soften dullness and mild dark marks. For serious hyperpigmentation you'll want something more targeted like tranexamic acid or vitamin C, but as gentle maintenance, PHAs pull their weight.
PHA vs AHA vs BHA: which should you pick?
- Oily, breakout-prone skin: BHA (salicylic acid) is still the best tool, because it's the only one that works inside the pore.
- Normal to dry skin wanting brightness and smoothness: an AHA like glycolic or lactic acid will get you there fastest.
- Sensitive, reactive or barrier-compromised skin, or acid beginners: PHAs. You trade some speed for a lot of comfort.
They're also a sensible downgrade path: if you've been over-exfoliating with stronger acids, switching to a PHA lets your skin recover without giving up exfoliation entirely.
How to use PHAs
PHAs turn up in toners, serums, masks and cleansers. The Ordinary, The Inkey List and Exuviance (whose founders patented the ingredient class) all make well-priced options.
- Start two to three evenings a week and build up. PHAs are gentle, but they're still acids.
- Apply to clean, dry skin, then follow with moisturiser.
- Don't stack them with AHAs or BHA in the same session; that defeats the entire point of choosing the gentle option.
- Patch test first, as with anything new.
- Wear SPF 30+ daily. PHAs cause less photosensitivity than AHAs, but sunscreen is non-negotiable with any exfoliating acid.
To sum it up
PHAs are the exfoliating acid for people who thought they couldn't use exfoliating acids: surface-level smoothing and brightening, built-in hydration, and a temperament mild enough for sensitive and rosacea-prone skin. If glycolic acid has always been too much for your face, gluconolactone is the name worth remembering next time you're reading a label.