PHA, short for polyhydroxy acid, is a gentle chemical exfoliant that smooths skin texture, boosts hydration, and fights signs of aging, all while causing significantly less irritation than traditional acids like glycolic or lactic acid. It works the same way other hydroxy acids do (loosening dead skin cells so they shed more easily) but its larger molecular size means it penetrates more slowly and doesn’t trigger the stinging and redness that keep many people away from chemical exfoliants.
How PHAs Work on Skin
PHAs belong to the same family as AHAs (alpha hydroxy acids), but their molecules carry multiple hydroxyl groups instead of just one. Those extra hydroxyl groups are what give PHAs their defining advantages: they attract and hold water against the skin, scavenge free radicals, and create a bigger overall molecule that can’t dive as deep as a smaller acid like glycolic acid.
Gluconolactone, the most widely used PHA, has a molecular weight of 178 daltons compared to glycolic acid’s 76 daltons. That roughly 2.3x size difference means gluconolactone absorbs gradually into the outer layers of skin rather than rushing through. The result is effective exfoliation with far less chance of irritation, burning, or visible redness.
The Three Main PHAs
Most skincare products use one of three polyhydroxy acids:
- Gluconolactone is the most common PHA and a naturally occurring component of human skin. It exfoliates, attracts moisture, and provides antioxidant protection. In lab studies, gluconolactone delivered up to 50% protection against UV radiation damage by scavenging free radicals, performing comparably to vitamin C and vitamin E in that specific model.
- Lactobionic acid is technically a “bionic acid,” a PHA with an extra sugar molecule attached. At 358 daltons it’s larger still, making it even gentler. It also inhibits enzymes that break down collagen and elastin, giving it a preventive anti-aging benefit beyond simple exfoliation.
- Maltobionic acid shares lactobionic acid’s molecular weight and sugar structure, offering similar hydration and enzyme-inhibiting properties.
Hydration and Skin Barrier Benefits
Unlike most exfoliants, PHAs actually strengthen the skin’s moisture barrier rather than temporarily weakening it. Each PHA molecule has multiple hydroxyl groups that hydrogen-bond with water, pulling moisture from the environment into the outer layer of skin. This humectant action makes PHAs function as both an exfoliant and a moisturizer in one ingredient.
Clinical testing has shown that gluconolactone reduces transepidermal water loss, which is the rate at which moisture escapes through the skin’s surface. Traditional AHAs like glycolic acid and lactic acid don’t provide the same barrier-strengthening effect and can actually compromise barrier function at higher concentrations. This distinction matters for anyone dealing with dryness, eczema-prone skin, or conditions like rosacea where barrier integrity is already compromised.
Why PHAs Suit Sensitive Skin
The gentleness of PHAs isn’t just marketing. Their larger molecular size physically prevents them from penetrating as deep or as fast, which is the primary reason AHAs cause stinging in the first place. In clinical comparisons, PHA regimens delivered anti-aging results comparable to AHA regimens while producing less irritation, less stinging, and less burning.
PHAs also don’t increase the skin’s sensitivity to sunlight. This is a meaningful difference. AHAs are well documented to make skin more vulnerable to UV damage, which is why sunscreen is non-negotiable when using glycolic or lactic acid. Testing overseen by the FDA and the Personal Care Products Council found that gluconolactone did not cause a significant increase in sunburn cells after UVB exposure. You should still wear sunscreen with any exfoliant, but the added photosensitivity risk that comes with AHAs doesn’t appear to apply to PHAs.
How PHAs Compare to AHAs and BHAs
AHAs (glycolic acid, lactic acid) are smaller molecules that penetrate deeper and exfoliate more aggressively. They’re better suited for sun damage, hyperpigmentation, and more pronounced texture concerns, but they come with a higher irritation ceiling and increased sun sensitivity. BHAs (salicylic acid) are oil-soluble, so they work inside pores and are the go-to for acne and blackheads.
PHAs sit in a distinct lane. They exfoliate the surface, hydrate, protect against oxidative damage, and support the barrier. If your skin reacts badly to glycolic acid, if you have rosacea, or if you’re using other potentially irritating actives like retinol, PHAs offer a way to get exfoliation benefits without compounding irritation.
Concentrations and What to Look For
Over-the-counter PHA products typically contain between 4% and 10% gluconolactone or lactobionic acid. Some nighttime formulations go up to 10% to 14% total PHA concentration. The pH of the product matters too: hydroxy acids need to be formulated at a low enough pH to stay active, generally around 3.5 to 4.0, but PHA products can function well within this range without the same irritation risk as AHAs at comparable acidity.
When scanning ingredient lists, look for gluconolactone, lactobionic acid, or maltobionic acid. Gluconolactone is by far the most common in serums and moisturizers. Lactobionic acid shows up more often in products marketed for anti-aging or sensitive skin repair.
Pairing PHAs With Other Actives
PHAs layer well with most skincare ingredients precisely because they’re so gentle. You can use a PHA alongside retinol without the compounding irritation you’d risk by pairing retinol with glycolic acid. Many people use a PHA product in the morning and retinol at night, or apply both in the evening with the PHA going on first (thinner, water-based products before thicker ones).
Vitamin C serums also pair comfortably with PHAs. Both work in acidic pH ranges, and the antioxidant effects of gluconolactone complement vitamin C’s photoprotective benefits. If you’re building a routine around sensitive skin, a PHA exfoliant can often replace an AHA entirely while letting you keep stronger actives like retinoids or vitamin C without overloading your skin’s tolerance.