Polyhydroxy acids, or PHAs, are the gentlest chemical exfoliants in common use. The one you will see most often on an ingredient list is gluconolactone, with lactobionic acid a distant second. PHAs work the same way as AHAs such as glycolic and lactic acid, loosening the bonds between dead cells on the surface so they shed more evenly, but their molecules are much larger, so they penetrate slowly and rarely sting. They also hold water, which means they hydrate while they exfoliate, and the evidence suggests they do not increase sun sensitivity the way AHAs do. The trade-off is speed: a PHA will smooth and brighten more gradually than an AHA at the same strength. That makes PHAs the right choice for sensitive, rosacea-prone, dry or easily marked skin, and an unnecessary compromise for skin that already tolerates glycolic acid well.
What Are PHAs?
PHAs are a family of acids with several hydroxyl groups (the 'poly' in polyhydroxy) arranged along a sugar-like backbone. They were developed in the 1990s by the same dermatologists who first popularised AHAs in skincare, specifically to get the benefits of AHAs with less irritation.
Three show up in skincare:
Gluconolactone is by far the most common. It is made from glucose, it is also used as a food additive (E575), and in water it slowly converts to gluconic acid, which is the form that does the exfoliating. Almost every product sold as 'PHA' uses it.
Lactobionic acid is gluconic acid bonded to a galactose sugar, which makes it roughly twice the size again. Researchers sometimes call it a 'bionic acid'. It is found mainly in professional and pharmacy brands, and is valued as much for its moisturising and antioxidant effects as for exfoliation.
Maltobionic acid is similar to lactobionic acid but bonded to glucose instead. It is rare outside a handful of clinical brands.
The point of a PHA is not that it exfoliates better. It is that it exfoliates with fewer side effects, which for some skin is the difference between using an acid and not using one at all.
How PHAs Differ from AHAs and BHA
All three groups loosen the 'glue' (corneodesmosomes) that holds dead skin cells together at the surface. The differences come from molecule size and how each one behaves in skin.
Size controls speed. Glycolic acid is the smallest exfoliating acid, at around 76 daltons, which is why it works fast and stings most. Lactic acid is slightly larger at about 90. Mandelic acid is around 152, and gluconolactone about 178. Lactobionic acid is around 358. A larger molecule moves into the skin more slowly and evenly, so it reaches the nerve endings that cause stinging in smaller amounts and creates less of the inflammation that leads to redness.
Hydroxyl groups attract water. This is what makes PHAs unusual. Those extra hydroxyl groups make gluconolactone and lactobionic acid humectants, in the same broad family as glycerin. The site's ingredient data rates gluconolactone's dryness risk as low and notes that it helps retain moisture, which is the opposite of what many people experience with glycolic acid.
BHA works in oil. Salicylic acid is oil-soluble, so it can travel into pores and clear the debris inside them. PHAs, like AHAs, are water-soluble and work mainly on the surface. If blackheads and congested pores are your main concern, a PHA is not a substitute for BHA; the salicylic acid guide is the better place to start.
What the Evidence Shows
The research on PHAs is smaller than for glycolic or salicylic acid, and much of it was published by the researchers who developed them, so it is worth reading with some caution. Even so, a few findings are consistent.
They are better tolerated. Studies comparing gluconolactone with AHAs on sensitive skin, including people with rosacea and eczema-prone skin, report less stinging, burning and redness. The site's data rates gluconolactone's irritation risk as low and lists sensitive, rosacea-prone, dry and post-procedure skin among its suitable uses.
They do not appear to increase sun sensitivity. One of the clearer findings comes from a study using 8% gluconolactone, which found no increase in sunburn cells after UV exposure, whereas glycolic acid at a similar strength did increase them. Our ingredient data reflects this: gluconolactone is listed with no sun sensitivity risk, while glycolic acid carries a warning. Sunscreen is still worth wearing every day, but you do not need to treat a PHA as a reason for extra caution in summer.
They improve texture and signs of ageing, slowly. Longer studies of gluconolactone and lactobionic acid at around 8–15% report smoother texture, more even tone and some improvement in fine lines over several months. The effects are real but more gradual than with glycolic acid at a comparable strength.
They have some antioxidant and protective effects. Gluconolactone and lactobionic acid both bind metal ions such as iron, which can drive oxidative damage in skin. Lactobionic acid has also been shown in laboratory studies to inhibit enzymes that break down collagen. These are mechanisms rather than proven visible results, but they help explain why PHAs turn up in anti-ageing formulas.
There is limited evidence for acne. A small early study found 14% gluconolactone reduced acne lesions with fewer side effects than 5% benzoyl peroxide. That is interesting, but it is one study, and for active acne the stronger evidence still sits with salicylic acid, azelaic acid and retinoids.
Who PHAs Are For
Sensitive and reactive skin. If glycolic or lactic acid leaves your face red, tight or stinging, a PHA is the most sensible next step. The sensitive skin ingredients guide covers what else belongs in that routine.
Rosacea-prone skin. Most exfoliating acids are a poor fit for rosacea, and the site's data lists rosacea under 'avoid if' for glycolic acid. A PHA, used once or twice a week, is the option dermatologists are most likely to suggest if you want to exfoliate at all. The rosacea guide explains why barrier support comes first.
Dry skin. Because PHAs attract water, they are one of the few exfoliants that do not tend to leave dry skin feeling drier. Lactic acid is the other good option here, and the dry skin ingredients guide compares them.
Skin that marks easily. On medium and deeper skin tones, irritation can leave post-inflammatory hyperpigmentation behind. A slow, even exfoliant reduces that risk. Mandelic acid is also a strong choice for this, and the acne scars guide explains how gentle exfoliation fits into fading marks.
Retinoid users. If you use retinol and want some exfoliation on other nights, a PHA is less likely to tip your skin into irritation than an AHA.
Who PHAs Are Not For
PHAs are a compromise, and not everyone needs one. If your skin is oily or resilient and you already use glycolic acid without any problems, switching to a PHA will mostly mean slower results for the same effort. The glycolic vs lactic acid guide is more useful for you.
They are also not the answer to clogged pores or regular breakouts. A PHA can make skin feel smoother, but it does not get into pores the way salicylic acid does.
On pregnancy, the site's data marks gluconolactone as 'caution' rather than 'safe'. Its large molecule means very little is likely to be absorbed, and it is generally considered lower risk than AHAs or retinoids, but there are no dedicated pregnancy studies. Low-strength leave-on products are likely fine; check with your midwife, GP or pharmacist if you are unsure, particularly before using a high-strength treatment. The pregnancy-safe skincare guide covers the wider picture.
Where We Differ: 'Gentle' Is Not the Same as 'Better'
PHAs are often marketed as the next generation of exfoliating acid, as if they replace AHAs. We see it differently. A PHA is a tool for a particular kind of skin: one that reacts to AHAs, or one where irritation causes problems of its own. For that skin, a PHA is often the best exfoliant available, because the one you can use consistently beats the one you have to stop using after a week.
For everyone else, the gentleness comes at the cost of speed, and there is no reason to choose it over an AHA you already tolerate. The useful question is not 'which acid is best?' but 'which acid can my skin use regularly without irritation?' For a lot of people that answer is lactic or mandelic acid, and PHAs are worth trying when those are still too much.
How to Use PHAs
Start with two or three times a week. Most people tolerate PHAs well, but it is still worth starting slowly and building up. Many people end up using a leave-on PHA toner daily; others find every other day is plenty.
Choose your format. A rinse-off cleanser with PHA is the gentlest way to start, because the acid spends less time on the skin. A leave-on toner or serum does more. Typical leave-on strengths are 3–15%, and the site's data notes that published sun sensitivity research used 8%. Most toners sit at the lower end of that range.
Apply to clean, dry skin, before thicker serums and moisturiser. A PHA toner can be used morning or evening. Because it does not increase sun sensitivity, morning use is reasonable, although evening suits most routines better.
Pairing is easy. PHAs sit comfortably with niacinamide, hyaluronic acid, ceramides and other hydrating ingredients, which is why several PHA products already include niacinamide. On the nights you use a retinoid or a stronger acid, skip the PHA at first. Once your skin is settled, some people combine them, but there is little to gain from stacking exfoliants. The layering actives guide explains the order of application.
Finish with moisturiser and wear sunscreen. Barrier support, especially a moisturiser with ceramides, makes any exfoliant easier to tolerate.
Stop if it stings persistently. A brief tingle is normal for some people. Burning, lasting redness or flaking means your skin wants a break.
Products Worth Considering
The Inkey List's PHA Toner (around £13.00 for 100ml) is the most straightforward way to try a PHA. It pairs 3% gluconolactone with 3% niacinamide and aloe, and the formula is short. At that strength it is a gentle everyday toner rather than a resurfacing treatment, which is exactly what most people looking for a PHA want.
Cetaphil's Gentle Exfoliating SA Cleanser (around £14.00 for 236ml) combines gluconolactone with mandelic acid, salicylic acid and niacinamide in a rinse-off cleanser for face and body. Because it washes off, it is a low-risk way for sensitive or acne-prone skin to get a little exfoliation, and the salicylic acid adds some pore-clearing benefit.
Cetaphil's Gentle Clear Triple Action Blemish Serum uses the same idea in a leave-on format, with gluconolactone, salicylic acid, succinic acid and niacinamide, for blemish-prone skin that does not tolerate stronger acids.
The Ordinary's PHA 5% Exfoliating Lip Serum (around £7.60) uses gluconolactone with ectoin and glycerin to smooth flaky lips, one of the places where a gentle acid makes the most sense. For rough skin on arms and legs, The Inkey List's PHA Body Water Cream (around £13.00 for 150ml) is a lightweight body moisturiser with 3% gluconolactone.
If a PHA turns out to be gentler than you need, The Ordinary's Mandelic Acid 10% + HA (around £7.40) and Lactic Acid 5% + HA (around £7.70) are the next steps up. The mandelic acid guide explains how to choose between them. You can browse the wider toner, cleanser and exfoliator ranges in the shop.
Common Mistakes
Expecting AHA results. A low-strength PHA toner will not give you the overnight glow of a 10% glycolic acid. Judge it after six to eight weeks of regular use.
Stacking exfoliants. Using a PHA toner, an AHA serum and a BHA cleanser in the same routine undoes the point of choosing a gentle acid. Pick one exfoliant per routine.
Using it for the wrong job. PHAs smooth the surface. They do not clear deep congestion, and they will not fill indented scars.
Assuming 'gentle' means no reaction. Low risk is not no risk. Patch test, especially if your skin is currently irritated or recovering from a stronger treatment.
Frequently Asked Questions
What does PHA do for skin? PHAs gently exfoliate the surface, which smooths texture and helps even out tone, while also attracting water to the skin. They are much less likely to sting or cause redness than AHAs.
Is PHA better than AHA? Not better, but gentler. AHAs such as glycolic acid work faster and more strongly. PHAs suit skin that finds AHAs irritating, including sensitive, rosacea-prone and dry skin.
Can I use PHA every day? Many people can, particularly with a low-strength toner. Start two or three times a week and build up if your skin is comfortable.
Can I use PHA with retinol? Yes, though it is best to use them on alternate nights at first. Once your skin has adjusted to both, some people use a gentle PHA toner before retinol, but watch for irritation.
Can I use PHA with niacinamide or vitamin C? Niacinamide pairs very well with PHAs, and some products combine them. Vitamin C can be used in the morning with a PHA in the evening if you want to keep things simple.
Do PHAs make you sensitive to the sun? The evidence suggests gluconolactone does not increase sun sensitivity, unlike AHAs. Daily sunscreen is still recommended for everyone.
Is PHA safe for sensitive skin? It is the exfoliant most often recommended for sensitive skin, but patch test first, and avoid using it on broken or very irritated skin.
What is gluconolactone? It is the most common PHA in skincare, made from glucose. It exfoliates gently, acts as a humectant and has antioxidant properties. See all products containing gluconolactone for the full range on the site.
.png?sw=450&sh=450&sm=fit&q=85)
