Everything You Need to Know About Polyhydroxy Acid (PHA)

There's a reason acid-infused skincare formulas are a mainstay on counters and vanities: Few ingredients can resurface, exfoliate, clarify, and make skin glow quite like they can. While there are a variety of acids in skincare that serve different roles for different skin types, PHA is a new breed of acid that boasts a slew of benefits. So, what is PHA? We spoke to experts to learn more about one of the largest skincare acids in the game. Keep reading to learn more about polyhydroxy acid (PHA) and why it should be in your skincare lineup.

What Is PHA?

PHAs, also known as polyhydroxy acids, are the newest acid that acts as an exfoliant. "PHAs 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 Ee Ting Ng, a cosmetic chemist and molecular biologist.

PHAs are often referred to as an "entry-level" chemical exfoliant, and for good reason. "Their larger molecular size means they sit closer to the surface of the skin, gently loosening dead skin cells without penetrating too deeply or causing irritation," says dermatologist, Alexandra Bowles, D.O. What’s exciting about PHAs is that they’re not just exfoliators—they also act as antioxidants and hydrators, making them a triple win for anyone looking to brighten and smooth their skin without the sting. "PHAs are used on the skin for their exfoliating, skin-smoothing, moisturizing, and anti-aging benefits, and may be a good alternative in patients with sensitive skin, including those with rosacea and eczema, who cannot tolerate AHAs and BHAs," adds dermatologist, Y. Claire Chang, MD.

Benefits of PHA

PHAs pack tons of benefits. It repairs the skin, exfoliates away dead skin, and reduces the appearance of skin damage. Other benefits include:

• Great for sensitive skin: According to Dr. Chang, PHAs are a lot gentler on the skin because they have a larger molecular 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, meaning they "help the skin retain moisture and
• can lead to improved skin texture and firmness over time," says dermatologist, Tiffany Libby, MD.
• 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 (poly-hydroxy acids like lactobionic acid) are similar to alpha-hydroxy acids, but they are more superficial—acting and less irritating," says dermatologist, Jennifer L. MacGregor, MD. "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 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 slow and see how you go.

Then you have your BHAs, or beta-hydroxy acids, which are 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—the new-gen AHAs, if you will. "PHAs are used to improve the tone and texture of your skin, but without extensive loss of surface skin cells and without commonly experienced irritation from AHAs," says dermatologist, Rachel Nazarian, MD. "PHAs can be found in facial pads, toners, and even leave-on lotions."

Side Effects of PHA

The good news is that PHAs aren't 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.

"While PHAs are generally well-tolerated, overuse can lead to skin irritation or dryness," says Dr. Libby. "I generally advise starting with lower concentrations or frequency and gradually increasing as the skin adjusts. If tolerated well, PHAs can be used daily. PHAs can make the skin more photosensitive, so daily application of sunscreen is crucial."

Skin Considerations

The best part? PHAs can be used with any skin type, from dry to oily, and sensitive skin types can even benefit from using this gentler acid. "PHAs are one of the best-tolerated chemical exfoliants and can be used by just about everyone, although I always recommend starting with infrequent use, monitoring for allergy, and avoiding areas of broken skin," says Dr. Nazarian, adding that those with acne-prone skin should be cautious of any irritation.

How to Use It

PHAs are used in a ton of products and 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 that 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. "PHAs also layer beautifully with most skincare ingredients, including hyaluronic acid, ceramides, and even some retinoids," adds Dr. Bowles. "If you're using a physical exfoliant or other active ingredients, though, try to space them out to avoid over-exfoliating."

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. Dr. 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."