Everything You Need to Know About Polyhydroxy Acid (PHA)

It feels like the entire skin-curious collective has fallen hook, line, and sinker for acid-infused skincare formulas, and that's largely due to the fact that few ingredients can resurface, exfoliate, clarify, and make skin glow quite like them.

If you're properly clued up (and you should be—acids are some serious business), you'll understand that there are a variety of acids that each serve a different role. Sorting your salicylic acid serums from your glycolic acid toners is vital in ensuring you're using an acid that's right for your skin type. But just as we finally understood the difference between AHAs and BHAs (clueless? Don't worry, we've got a refresher course coming up), a new breed of acid is cropping up on our feeds to present its own set of persuasive benefits: PHAs. We spoke to experts to get the skinny on the largest skincare acids.

Read on to learn more about PHA and why it should be in your skincare lineup.

What Is PHA?

PHAs, also known as polyhydroxy acids, are the newest acid to take over ingredients lists and newsfeeds all over the beauty world. "PHAs (Poly-hydroxy acids) fall under the AHA family. They are much larger in size compared to the more common AHAs like glycolic and lactic acids. Examples of PHAs are lactobionic acid and gluconolactone. Essentially, their benefits are the same as AHAs," explains Ng.

Chang elaborates, "Because of their larger structure, PHAs do not penetrate as deeply into the skin but rather work on the outer layers of the skin. They tend to be less sensitizing and gentler as compared to other chemical exfoliants. PHAs are used on the skin for their exfoliating, skin smoothing, moisturizing, and anti-aging benefits... PHA may be a good alternative in patients with sensitive skin, including those with rosacea and eczema, who cannot tolerate AHAs and BHAs."

Benefits of PHA

• Great for sensitive skin: According to Chang, PHAs are a lot gentler on the skin because they have a larger molecule size. That means they take a little longer to properly sink in, and they'll never travel quite as deep as a straight-up AHA.
• Non-irritating: Sensitive skin types should be able to apply a PHA with little-to-no stinging or irritation.
• Maintain skin hydration: PHAs are humectants (meaning they retain moisture reserves) and contribute to the most glowing of complexions.
• Anti-inflammatory: These acids may be best known for their exfoliation properties, but they come armed with tons of anti-inflammatory and antioxidant properties.
• Fight glycation: PHAs combat glycation, a process that weakens collagen and elastin in your skin.

AHA vs. BHA vs. PHA

"PHAs (polyhydroxy acids like lactobionic acid) are similar to alpha-hydroxy acids but they are more superficial—acting and less irritating," says MacGregor. "Think of these like a light and bright peeling agent that is more user-friendly. A dry, sensitive skin type with pigment and a little sun damage, for example, might use PHAs followed by moisturizer (or combined) to brighten, smooth, hydrate, and plump the skin—a quick refresh."

First, you've got your AHAs (alpha-hydroxy acids), and that covers your glycolic, citric, and lactic acids. They all have their own strengths, but they mainly work by nibbling away at skin cells to reveal more glowy skin hiding underneath. AHAs can be pretty intense, so depending on the concentration of your product, you probably want to limit your usage to once or twice a week. As always, start off slow and see how you go.

Then you have your BHAs, or beta-hydroxy acids, which is where salicylic acid can be found. This type of acid is brilliant at flushing out blocked pores, which is why you always hear it recommended for things like acne or keratosis pilaris—that rough skin you have that never quite seems to go away.

And then comes PHAs or poly-hydroxy acids—new-gen AHAs if you will. "They're a special type of AHA that strengthens the skin's barrier function and fights the signs of aging without the irritation of the classic AHA," Dr. Frances Prenna Jones explains.

Side Effects of PHA

The good news is that PHAs aren't really known for having side effects—that's kind of the whole point. Instead of going deep into your skin, they gently wash away any debris that's sitting on top of it. It's why they're so beloved, and such an easy ingredient to use. However, they are still acids, so if you have sensitive skin, do a patch test.

How to Use It

PHAs are used in a ton of products, and in a few different ways. "They are best used in products that are left on the skin for an extended period to give them sufficient time to loosen the bonds between the outermost epidermis/skin cells. They can be incorporated into any product type—liquid exfoliant, toner, mask or moisturizer," says Ng.

A lot of AHA solutions will have PHAs in them to clean up the surface-level debris AHAs miss. Sometimes, PHAs are added as an extra exfoliating factor to a non-exfoliating product so the dead skin cells are washed away and the properties of the product—usually a serum—can be seen. And sometimes, PHAs are the main selling point.

But that's not all: PHAs may also be the most versatile of the acids, which means they can be combined with plenty of other treatments. Chang explains: "PHA can be combined with other ingredients or dermatologic procedures to provide additional benefits to therapy. PHA can be combined with retinoids when treating acne or photoaging. PHA can be used in conjunction with hydroquinone to improve skin pigmentation and aging. PHA may also be used after cosmetic procedures, such as laser and microdermabrasion, but should be done in consultation with your dermatologist."

The Best Products With PHA

Lixir Night Switch PHA/AHA 10% $14.00

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We were massive fans of Lixir when it first launched (and not only because it's the most Instagrammable brand since Glossier) because it offers pared-back formulas without a load of fluff or filler ingredients. This night serum promises to chip away at the build-up of dead skin cells on the surface, so it is perfect if your skin appears to be wearing a winter coat of dullness.

Glossier Solution $24.00

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There's a lot going on in this formula, so we wouldn't recommend using it every day—and definitely not if your skin is super sensitive. But, it contains a blend of AHAs, BHAs, and PHAs that seem to be having a remarkable effect on clearing up cases of acne. Just go steady.

Zelens PHA+ Bio-Peel Resurfacing Facial Pads $129.00

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These pads promise to buff away layers of dead skin and encourage skin density, making skin look and feel more even. They are also meant to help lock in water from the atmosphere to amp up that glossy smoothness of supermodel skin.

Herbivore Bakuchiol $43.00

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If you haven't heard of bakuchiol, most of what you need to know is that it's a non-photosensitive, gentler version of a retinol. This serum—which is safe for even the most sensitive of skin, although you should always do a patch test—has been combined with PHAs so it doesn't just increase cell turnover, but sloughs off the dead skin that results from it.

Juice Beauty Green Apple Peel Full Strength $49.00

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Juice Beauty has had a green apple line for a long time, and one of its stars is this peel. Alpha, beta, and poly-hydroxy acids give it some serious exfoliating power, while vitamins from the green apple are meant to provide nourishment for your skin.