a woman holding a bottle of serum with PHAs

Ask a Dermatologist: What Are PHAs?

Last Updated: April 8, 2022

Whether you're a skincare fanatic or just starting your clean beauty journey, acid exfoliants should definitely be on your list of must-haves. We asked a dermatologist all about the benefits of PHAs and how to use them for brighter, smoother skin.

You’ve heard the buzz and felt the tingle of AHAs and BHAs — but there’s a new acid in town, and it means (gentle) business. PHAs are a godsend for folks with sensitive skin who want the glow-inducing benefits of acid exfoliants – without the irritation. But don’t get it twisted — they’re not just for sensitive skin! We spoke with dermatologist Anna Chacon to better understand PHAs and their role in skincare.

What are PHAs?

PHA, or polyhydroxy acid, is a type of chemical exfoliator. They’re related to the more well-known AHA (alpha-hydroxy acid) and BHA (beta-hydroxy acid). “PHAs work on the skin by breaking down the sugars in dead skin cells, causing the bonds between those cells to loosen. As the cells come loose, they shed,” says Dr. Chacon.

PHAs are considered the “gentle giant” of acid exfoliants because they have a larger molecule size than AHA or BHA. Is bigger really better, though? “The larger molecules in PHAs prevent them from deeply penetrating the skin, making them a more mild alternative to AHAs and BHAs — both of which have smaller molecules that go far beneath the surface of the skin.”

Innuendos aside, PHAs are an effective exfoliator that have many of the same benefits as their cousins – just with fewer potential side effects.

illustration of Chamomile flower

What are the different types of PHAs?

These are the three most common types of PHAs used in skincare products. If you see ‘em listed in your toner, serum, or moisturizer, you’ve got a PHA on your hands.

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What’s the difference between AHA, BHA, and PHA?

“AHA, BHA, and PHA are all acid exfoliants, so they work by the same chemical process of breaking down cell bonds and sloughing off dead skin,” says Dr. Chacon. The true difference is in the details.


AHA exfoliants, like glycolic acid and lactic acid, have natural hydrating abilities which makes them a good choice for dry skin. They also help minimize pores, treat hyperpigmentation, and are ideal for people with aging skin.” The downside? “AHAs are a more potent acid that drives deeply into the skin — this leads to more drastic results, but can also cause redness and irritation.”


If you’ve got acne-prone skin, you’re probably familiar with the most famous BHA — salicylic acid. “BHA exfoliants like salicylic acid help break down oil by moving deeper into the skin to remove debris and clear out pores. They also have anti-inflammatory and anti-bacterial properties, making them a prime player in the treatment and prevention of breakouts.”


Plot twist — PHAs are actually a type of AHA. “PHAs are a very gentle form of AHA,” says Dr. Chacon. “Like AHAs, PHAs are beneficial for aging skin and to boost hydration. Their larger molecule size helps them gently exfoliate the surface of the skin without the irritation associated with AHAs.”

PHA benefits

Hydrates skin

“PHAs are humectants – which means they’re able to bind to water molecules to help skin stay hydrated.” More hydration equals plump, glowing skin.

Exfoliates dead skin cells

Exfoliation cleans pores, draws out impurities, brightens dull skin, prevents acne, and helps skincare products absorb faster and more deeply. How’s that for a glowing review?

Combats glycation

“Glycation happens when sugar cells attach to collagen and elastin, effectively weakening them,” says Dr. Chacon. PHAs help fight against glycation to keep your skin smooth and supple.

Reduce signs of aging

The whole PHA package — exfoliation, hydration, combating glycation — coupled with the fact that PHAs also have antioxidant properties, gives this gentle giant wrinkle-reducing superpowers.

Get smooth skin all over with our top 10 tips to exfoliate your face and body.

How to use PHAs

PHAs are the Type O of skincare ingredients — meaning they’re gentle enough to be used in all kinds of products, even if the product isn’t targeted toward exfoliation. PHAs are used in serums, toners, and moisturizers to provide a light exfoliating boost to allow the product’s results to shine through. They’re also used alongside AHAs or BHAs to sop up and slough off any oil or dead skin lingering on the surface of your skin.

Can I use a PHA everyday?

Just because PHAs are a gentler acid doesn’t mean they’re safe to use everyday — at least not at first. “Start out using PHA products two to three times a week on alternating days,” says Dr. Chacon. “After a week, you can use it every other day. If your skin doesn’t show signs of irritation with increased use, you can use PHAs everyday.”


What products shouldn’t be used with PHAs?

The beauty of PHAs is that they play nice with pretty much everything – including AHAs and BHAs. Niacinamide, retinol, hydroquinone, and vitamin C can all be used in conjunction with PHAs. Dr. Chacon advises that small patch tests should be done first (preferably on your forearm – not your face) to make sure your skin doesn’t have a negative reaction to PHA mixed with other active ingredients.

How do you layer PHA in your skincare routine?

How you layer PHAs depends on the type of product you’re using. If it’s an exfoliating toner, use it after you’ve washed your face but before you apply any serums or moisturizers. Dr. Chacon notes that while PHAs don’t cause as much sun sensitivity as other acids, it’s still important to follow up with sunscreen if you’re using any PHA products during the day.

Skin hydration illustration

PHA side effects

“PHAs don’t have harsh side effects the way other acid exfoliants do. If you have especially sensitive skin, do a patch test or consult with your dermatologist before integrating PHAs into your skincare routine,” Dr. Chacon says. PHAs are safe for people with eczema, rosacea, and acne-prone skin.

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