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Buzzy Beauty Ingredient of the Moment: Polyhydroxy Acid

Everything you know about the skin-care superpowers of PHAs.
Glossier Solution. Photo: Courtesy of Glossier

Glossier Solution. Photo: Courtesy of Glossier

Welcome to our series "Buzzy Beauty Ingredient of the Moment," the premise of which is pretty self-explanatory: In each installment, we'll explore an ingredient that's currently trending in the industry, springing up in a variety of different products lining the beauty aisle. We'll consult experts to find out about the science behind it — and why it's having a major moment right now.

Sometimes I wish I could give high school another go. Sure, I could do without the uniforms and the social awkwardness — but chemistry class would have been so much more interesting had I known that the glowiness of my future skin depended on understanding the core function of hydroxy acids. I'd raise my hand wildly and force the teacher to address all my burning questions: What's the difference between alpha- and beta- hydroxy acids? Why do they give some people a flawless complexion but give me a rash? Is there something milder, but equally effective, I can try instead? It's better late than never though, and 12 years post-graduation, I finally have my answer: AHAs and BHAs have a class of distant relatives — polyhydroxy acids, or PHAs — that were practically made for the sensitive-skinned.

For the uninitiated, hydroxy acids fall under the umbrella of chemical exfoliants. These substances rely on chemical reactions to loosen dead cells on the skin's surface and reveal the fresh, unblemished skin underneath, without the harsh sloughing of a scrub. The most well-known chemical exfoliators are BHAs, like salicylic acid, and AHAs, like lactic and glycolic acid. By speeding up skin's natural cell turnover rate, hydroxy acids offer a range of benefits, including eliminating blemishes, relaxing fine lines and wrinkles and evening out tone and texture — not to mention boosting the efficacy of all your other skin-care products, since they're not wasting precious active ingredients on dead skin cells.

The specialty of each particular hydroxy acid depends on its unique chemical makeup. As smaller, oil-soluble molecules, BHAs can travel deep into pores to shake up any clogged sebum — that's what makes salicylic acid products such effective spot treatments. AHAs are water-soluble, so they do most of their work on the outer layers of the skin. You typically find them in liquid exfoliators, like Biologique Recherche Lotion P50 (which features lactic acid) and Pixi Glow Tonic (a glycolic blend). But AHAs and BHAs do have one major flaw: the tendency to irritate sensitive faces.

Enter PHAs. "Polyhydroxy acids are the new generation of AHAs," Dr. Marko Lens, a dermatologist and the founder of skin-care brand Zelens, tells Fashionista. Like AHAs, PHAs are water-soluble, but they boast a significantly larger molecular size. "These larger molecules tend to limit how deeply [the formula] penetrates into the skin, and generally PHAs remain on top of the epidermis," explains Dr. Ronald Moy of DNAEGF Renewal. This surface-level exfoliation is gentle but effective, "smoothing the skin and unclogging pores with less irritation when compared to AHAs and BHAs," the dermatologist says. In other words, PHAs belong in every sensitive skin-care enthusiast's #shelfie.

"Most PHAs also demonstrate antioxidant properties," adds Dr. Lens. Antioxidants are frequently used in pollution-fighting skin-care products. These ingredients neutralize the effects of environmental damage on the skin, which can include everything from premature aging to inflammation; and are now considered as essential for skin health as a daily dose of sunscreen.

PHAs are also humectants, meaning they pull water molecules into the pores. "This allows for better moisturization than AHAs," says Dr. Moy.

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The combination of exfoliation and hydration is pretty much unheard of in the ingredient realm, but the magic doesn't stop there. This particular hydroxy acid also stimulates epidermal growth and can "improve skin barrier function," according to Dr. Lens. Considering the fact that most exfoliating agents, both physical and chemical, tend to impair skin's barrier and make it more susceptible to damage, PHAs have earned the oft-used but rarely deserved title of Miracle Ingredient.

To prove my point: "PHAs can be used by people with sensitive skin, including those suffering from rosacea and atopic dermatitis," notes Dr. Lens. Anyone who's dealt with either condition knows the life-changing — or at least skin-changing — implications of that statement. (I personally have chronic dermatitis and until now, I considered "exfoliator" a dirty word.) PHAs have even been shown to improve these issues over time, since they simultaneously slough away affected surface cells and strengthen newly-exposed skin.

"Too much can still be irritating, so it's important to 'listen' to your skin," warns Dr. Adarsh Vijay Mudgil, the medical director of Mudgil Dermatology. He recommends starting small by using a PHA-spiked product once or twice a week, then working up to daily application. And while the subtle exfoliation of PHAs may be just what reactive, compromised or dry skin needs, Dr. Moy notes that those with oily or mature skin may be better off sticking with BHAs or AHAs to achieve the desired blemish-fighting and texture-smoothing effects.

"PHAs can be found in toners and some exfoliating masks," Dr. Mudgil tells Fashionista. Notable mentions include Glossier Solution (which features a potent mixture of AHAs, BHAs and PHAs — and, as such, probably isn't the smartest pick for sensitive types) and Glow Recipe Avocado Melt Sleeping Mask

To find PHAs out in the wild (you know, the aisles of Sephora), look for the words gluconolactone, galactose and lactobionic acid on ingredient labels — or just shop our top PHA picks in the gallery below. Ahead, we've rounded up 11 products that deliver mild exfoliation and general glow-ification, minus the irritation.

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