Polyhydroxy Acids (PHA’s): What The Heck Are They?

Good news:

There’s a new family of hydroxy acids that are gentler and, dare I say, better than their more conventional counterparts.

Polyhydroxy acids—more commonly referred to as PHA’s—are a lot like AHA’s. They’ll improve texture, even out skin tone, and diminish fine lines. But, unlike AHA’s (and BHA’s for that matter), they’re way—and I mean WAYYY—less irritating.  

Cool, right?

Okay, let’s dive into more detail.

PHA’s Have a Larger Molecular Size

PHA’s were discovered by Dr. Eugene Van Scott and Dr. Ruey Yu—yep, the revolutionary geniuses behind AHA’s.

Since they’re a relatively new find, there isn’t much information about them quite yet.

What I can say is that PHA’s are similar to AHA’s.

There’s just one major difference between the two—PHA’s have a bigger molecule size.

Here’s a side-by-side view of the molecular structures of lactic acid (your traditional AHA) and lactobionic acid (PHA).

Molecule structure of lactic acid compared to lactobionic acid


Why does size matter?

For one, bigger molecules aren’t able to penetrate as deep as smaller molecules. Rather, they work their magic on your skin’s surface layer.

Another thing.

When they do absorb into your skin, they do so slowly.

These two things—namely, penetration and rate of absorption—make them gentle enough to use on sensitive skin.

The Benefits of Polyhydroxy Acids

Polyhydroxy acids aren’t going to slough off your skin like their more bullish big brothers, AHA’s and BHA’s.

Instead, they’ll offer a milder (and subtler) approach to exfoliation.

Beyond exfoliation, however, PHA’s offer a whole host of other benefits:

  1. Function as humectants (i.e. they bind and attract water).
  2. Lighten skin (and hyperpigmentation), especially when paired with hydroquinone.
  3. Have antioxidant capabilities.
  4. Calm acne.
  5. Won’t cause photosensitivity.
  6. Reduce fine lines and wrinkles.
  7. Gentle enough for sensitive skin.
  8. Strengthen your skin’s protective barrier.

There’s one benefit that stands above the rest.

A lot of people shy away from AHA’s—and all other exfoliants for that matter—because they’re photosensitizing.

Not PHA’s! I mean, you still shouldn’t skimp on sunscreen. But, you generally don’t have to worry about any excess sun damage!

Who Should Use Them?

PHA’s offer exfoliation without injury.

Rosacea sufferersone study found that PHA’s, used in combination with azelaic acid, can help reduce the redness (aka erythema) caused by rosacea.

Eczema sufferersanother study found that topical applications of lactobionic acid can curb the onset of eczema breakouts. That’s not surprising given the fact that PHA’s can strengthen the function of your skin’s outer layer.

While you can’t use PHA’s to cure either of these skin conditions, you can use them to manage your symptoms.

Plus, PHA’s won’t exacerbate your condition. So, you’re free to harness their exfoliating powers to smooth-out and plump-up your skin without the fear of burning, dryness, itchiness, or over-exfoliation (score!).

How Often Should You Use Them?

From what I understand, PHA’s are gentle enough to use on a day-to-day basis. Most of the in-vivo research has studied subjects based on a twice-a-day application.

As always, what works for one, may not work for another. So, if you’re not sure what your skin can handle, go slow. And build up accordingly.

Oh, and be careful.

Sometimes products containing PHA’s also contain more irritating ingredients. Please read the ingredients list to avoid any mix-ups.

The PHA Family Tree

Generally speaking, there are three types of PHA’s you’ll find in skincare products—gluconolactone, lactobionic acid, and galactose.

AHA’s Vs. PHA’s: The Battle Between Acids

Throughout this article, we’ve compared PHA’s to AHA’s—a lot.

But, how are they different?

And, more importantly, is one really better than the other?

Well to get started, let’s check-in with the first question.

A 12-week study (pioneered by Neostrata) compared the effects of AHA’s to those of PHA’s on 57 subjects. These are the features that they compared:

  • Fine Lines
  • Deep Wrinkles
  • Sallowness
  • Roughness
  • Firmness
  • Pore Size
  • Pigmentation
  • Irritation (self-reported)
  • Etc.

While most results were statistically similar (i.e. both do a good job at improving the items in the list above), the researchers determined that AHA’s were better at improving sallowness and skin elasticity (via a pinch recoil test). Whereas PHA’s were winners on the irritation front—they were less likely to cause redness, burning, dryness, etc.

Apart from this study, there’s another key difference that I’d like to point out again—sun sensitivity.

To cut it short, AHA’s cause photosensitivity. PHA’s don’t.

Ultimately, the “better” hydroxy acid comes down to personal preference.

If you’re a sensitive-skinned sun-tanner, go with PHA’s. If not, AHA’s will do you justice (usually at a cheaper price).

The Caveat

Getting your hands on this stuff isn’t easy.

Since most companies haven’t had the chance to utilize PHA’s (because it’s been under patent for so long), there aren’t many products on the market yet.

And, the products on the market are usually on the more expensive side of things.

Pregnant women, just to be on the safe side:

Consult with your doctor before adding PHA’s into your regimen.

Final Thoughts

PHA’s can be a good introduction to chemical exfoliants because they’re gentle as heck and almost universally tolerated.

But as I mentioned in the last section, PHA’s can be quite pricey. So, if you’re going to buy a product, buy something that stays on your skin—no cleansers, please. This way, your skin will be able to soak-up some real benefits. I wrote an article about 4 highly-regarded PHA products—check it out here.

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