The Skin-Transforming Ingredient You're About To See Everywhere

Scary as they might sound at first, there's nothing like the exfoliating, glow-giving benefits of using an acid in your skin care. But the catch-all term doesn't even begin to cover the wide range of different acids you'll find used in various formulations, all serving their own purposes — and it turns out that there are even a few under-the-radar types you (yes, you) might be missing.
Alpha-hydroxy acids, or AHAs, are perhaps the type you'll see mentioned most frequently in the context of skin care. Glycolic, citric, lactic, and mandelic acids are common in many formulas, but despite their shared ability to break down the binding and buildup between skin cells, they're not alike in every way — far from it, in fact.
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"Glycolic acid is good for controlling oil production and whitehead formation," explains dermatologist Justine Hextall of Tarrant Street Clinic. Dr. Hextall says that, like retinoic acid, continued use of citric acid will result in a thicker epidermis over time, meaning stronger, healthier skin. Lactic acid is an excellent antimicrobial that reduces pigmentation, breaks down the gunk in clogged pores, and, as Dr. Hextall explains, helps to "restore the skin's naturally acidic pH, which is very important for optimal skin-barrier function."
And then you have the beta-hydroxy acids, or BHAs, which you probably best know as salicylic acid. "Salicylic acid is especially helpful because it likes oil, and it's keratolytic, meaning it breaks down the keratin that blocks pores and causes bumpy skin and acne lesions," Dr. Hextall explains. That quality makes it particularly useful in treating all forms of acne.
But while AHAs and BHAs are in countless skin-care formulations across the market, there's a third, lesser-known acid group that's recently seen a surge in visibility. Polyhydroxy acids, or PHAs, are being touted as the perfect acid for sensitive skin, especially for those who have tried the more common forms and found them too irritating for even occasional use. "PHAs are basically a more gentle form of AHAs," Dr. Hextall says. "As the molecules are larger, they can't pentrate as deeply into the skin, so any exfoliation is more gentle. They also have some antioxidant and anti-inflammatory effects, which is also great for sensitive skin."
The benefits don't end there. PHAs are also humectants, meaning they can retain moisture, and actually help hydrate the skin while gently exfoliating. They also strengthen the skin's barrier function, which is especially helpful for rosacea and eczema-prone skin types, which so desperately need that skin-strengthening factor. They're also what Dr. Hextall calls "tolerable," which means that they can be combined with retinoids for even better anti-aging results, without causing any irritation.
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PHAs are steadily gaining a foothold in the skin-care universe, but for the time being, you still have to look for them; unlike AHAs and BHAs, they're not jumping out at you from every Sephora shelf. The PHA gluconolactone is featured in Glossier's Solution exfoliating liquid and the PHA Moisture Renewal Power Cream from K-beauty favorite CosRx; lactobionic acid, another PHA, is the star ingredient in Zelens PHA+ Bio Peel Resurfacing Facial Pads.
Be sure to keep an eye out for more and more formulas harnessing the sensitive skin-friendly powers of this unique acid — all of your favorite brands might just be hopping on the latest skin-brightening bandwagon before you know it.