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Chances are, if you’re into skincare half as much as we are, you’ve heard about alpha-hydroxy acids (AHAs) and beta-hydroxy acids (BHAs). Each work slightly differently and provide a host of rejuvenating and brightening benefits, including fighting off bacteria and speeding up skin cell rejuvenation. But there is another, lesser-talked about class of skincare acids that warrants just as much of your attention: poly-hydroxy acids, or PHAs. Larger in molecular size and thought to be less irritating than their BHA and AHA counterparts, PHAs are thought to be ideal for those with sensitive skin who still want the benefits of chemical exfoliation.
To find out the full scoop on PHAs, including where they come from, what they do and who should use them, we reached out to a board-certified dermatologists Dhaval Bhanusali of Hudson Dermatology and Laser Surgery, Robert Finney of Heights Dermatology and Laser, and Dr. Sheila Farhang to get the details on this overlooked acid.
Meet the Expert
Dr. Dhaval Bhanusali specializes in medical and cosmetic dermatology at Hudson Dermatology and Laser Surgery in Manhattan. He serves as a media advisory member for the American Academy of Dermatology and a medical expert for many companies in the field, including Johnson& Johnson and Solta.
What are PHAs?
PHAs are a type of chemical exfoliant, which means they work to help slough off the top layers of the skin, and they are technically second-generation acids (whereas BHAs and AHAs are siblings, think of PHAs as their cousin). In addition to their exfoliative benefits, PHAs “also act as a humectant by binding water and keeping moisture in the top layers of skin,” Finney explains. On top of that, “they can also help minimize pigmentation, unclog pores and reduce the appearance of fine lines.”
Meet the Expert
Dr. Robert Finney, MD is a board-certified dermatologist and dermatologic surgeon, as well as fellowship-trained in cosmetics. He practices out of Heights Dermatology and Laser in Brooklyn.
Since they are often blended together with BHAs and AHAs, you could already be using them. The most common PHA names to look out for on your product ingredient lists include gluconolactone and lactobionic acids, Farhang says.
How do PHAs differ from AHAs and BHAs?
“PHAs are similar in mechanism to both BHA and AHA, but they are larger molecules which ensures they do not penetrate as deeply,” Finney explains. Although this may sound bad, because you want your skincare products to penetrate, it can actually be helpful for more sensitive skin types. "This helps them work on the superficial layers of the skin and provide gentle exfoliation, rather than more aggressive forms that may not be always necessary," Bhanusali says. Compared to BHAs specifically, which tend to work best for acne and oiliness, PHA's "also target more surfacing [issues like] brown spots, texture [and] fine lines," Farhang says.
Meet the Expert
Dr. Sheila Farhang, MD, is a board-certified, dual fellowship-trained dermatologist and cosmetic surgeon living in Tucson.
Additionally, Farhang says that compared to AHAs and BHAs, PHAs also penetrate the skin at a slower rate which, again, is beneficial for those with sensitive skin, or those just looking for a gentler route of chemical exfoliation.
Who should try PHAs?
As mentioned PHAs are an ideal acid for sensitive skin types because they get the job done with less irritation than their more well-known acidic cousins (AHAs and BHAs). “These are a great alternative for those with want to target their dark spots, fine lines, etc. for skin renewal but have sensitive skin, rosacea, and/or eczema,” Farhang says. But if you have combination or oily skin, you can also benefit from incorporating PHAs into your routine—they just won't be as strong as AHAs or BHAs.
What are the best ways to use PHAs?
As is the case with many other acids, PHAs are often combined with AHAs and BHAs into toners, such as Glossier’s Solution ($24), which contains a 10 percent blend of all three, or cult-favorite Some By Mi 30Days Miracle Toner ($16). You'll also find it in masks—including leave-on treatment masks, like Glow Recipe's popular Avocado Melt Sleeping Mask ($45).
Since it is suitable for sensitive skin, PHAs are also ideal for eye cream, like the Neostrata PHA Eye Cream ($54), which is formulated with a 4 percent PHA blend that can “help to lightly exfoliate and brighten the area without irritating,” Bhanusali says.
Next, learn about yet another acidic skincare ingredient, phytic acid.