PHA (Polyhydroxy Acid)

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. 

POLYHYDROXY ACID (PHA)

TYPE OF INGREDIENT: Exfoliant.

MAIN BENEFITS: Repairs skin, exfoliates away dead skin, reduces the appearance of skin damage.

WHO SHOULD USE IT: PHAs are usually safe for all skin types, but especially for those with oily or acne-prone skin.

HOW OFTEN CAN YOU USE IT: To start, try using PHAs three times a week. You can use it in the form of a toner, a face wash, or even a serum.

WORKS WELL WITH: Other acids in low concentrations.

DON'T USE WITH: Other acids in very high concentrations, retinoids if you're particularly sensitive.

What exactly are PHAs?

PHAs, also known as polyhydroxy acids, are the newest acid to take over ingredients lists and news feeds all over the beauty world. PHAs are gentle chemical exfoliants that fall under the AHA family. They are much larger in size compared to the more common AHAs like glycolic and lactic acids. The most common PHAs are gluconolactone, galactosen and lactobionic acid. Essentially, their benefits are the same as AHAs, they exfoliate dead skin cells from the surface, which helps skin be smoother and more even.

Because of their larger structure, PHAs do not penetrate as deeply into the skin but rather work on the outer layers of the skin. PHAs tend to be less sensitizing and gentler as compared to other chemical exfoliants. PHAs are used on the skin for its 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.

How are PHAs different from AHAs and BHAs?

"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—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 strengthen the skin's barrier function and fight the signs of aging without the irritation of the classic AHA," dermatologist Frances Prenna Jones explains.

Are PHAs good for skin?

With regular use, PHAs can lead to brighter, smoother, more hydrated skin and an overall enhanced glow. "Polyhydroxy acids are wonderful because they are something you can use at home regularly to chemically exfoliate the skin without undergoing any major procedures," says Dr. Weinstein. "They are low-cost and offer anti-aging benefits."

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: If you have sensitive skin you'll probably 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 you definitely have a recipe for the most glowing of complexions.

• Anti-inflammatory: These acids may be best known for their exfoliation properties, but their real claim to fame should be that they come armed with tons of anti-inflammatory and antioxidant properties.

• Fight glycation: PHAs even combat glycation, a process that weakens collagen and elastin in your skin.

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.

Who should use PHAs?

Virtually anyone can use PHAs, but those with sensitive skin may get the most benefit from, since they likely won't cause irritation like other chemical exfoliants or face peels might. "They also have a hydrating quality, so in addition to exfoliating, they will help with hydration which is especially important with sensitive skin," says Dr. Weinstein. PHAs are also gentle enough to be used during pregnancy, and they're perfect for acne-prone skin, as they help even out texture and tone. Try Dr. Jart's Dermaclear Micro Water if you're looking to treat acne.

What types of PHAs are best?

Often, these PHAs are mixed together in products, so you can't go wrong — particularly if you're looking for an exfoliator for sensitive skin.

• Gluconolactone: The most popular of the PHAs, gluconolactone not only works to exfoliate your skin, it also hydrates and may offer some antioxidant benefits.
• Lactobionic acid: An oxidized form of milk, this acid works as both an exfoliator and a humectant, meaning it helps your skin retain moisture.
• Galactose: This PHA may sound familiar to you — that's because it's the sugar found in milk. This one is a bit less common than the other two, but it works to exfoliate your skin just as gently.

How often should you use PHAs?

In general, you can safely use PHAs three to four times a week, since they are more gentle than other acids. Keep in mind, the right amount depends on your individual skin type. "I always recommend starting slow and increasing as tolerated, which might look like starting twice a week, then increasing to three times a week and eventually every other day, if possible," Dr. Weinstein says.

Is it safe to use PHAs with ingredients like vitamin C or retinol?

Polyhydroxy acids play nicely with other active ingredients. PHAs can easily be incorporated into a routine that already includes products containing vitamin C or retinol — but again, be sure to start slowly to make sure there's no irritation. You can even try a serum like Herbivore's Bakuchiol, which is a gentle retinol alternative formulated with PHAs. Always layer your skincare products from thinnest to thickest, and wait for each product to dry before applying the next one.

Are there any side effects to PHAs?

"That’s the wonderful thing about PHAs — the side effects are minimal, and they’re very well tolerated," Dr. Weinstein says. When you first start using an acid, you can expect a small amount of irritation, according to Dr. Weinstein. "Major irritation in the way of increased and persistent redness, peeling and perhaps some itching should indicate that the product is too harsh or should be used less often," she says. Watch your skin carefully for signs that you should scale back on use, and only use once a week if you have other acids in the mix (like AHAs or BHAs).

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 of time 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 in order 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 are also 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."