What are PHA – The role of polyhydroxyacids in skincare | Ask Doctor Anne


Every now and then a seemingly new ingredient gets the spotlight and gets featured in more and more products. Take PHA for example, also known as polyhydroxy acids. After years of everyone talking about Glycolic, Lactic and Salicylic Acid, suddenly PHA made an appearance in Allure magazine, in The Inkey List products and in guides on how to exfoliate sensitive skin.


The role of Polyhydroxy Acids (PHA) in skincare
PHA – Everything you need to know


But what is their role in skincare? Are PHA something you must know about or just another attempt to get you to part with your money? What are they exactly, what do they do in the skin and who will benefit from introducing them into their routine?
Today we are going to talk about all that and I will list my personal recommendations at the end.


What are Polyhydroxy Acids (PHA)?

Polyhydroxy Acids belong to the group of Carboxylic Acids, which also has Alpha-Hydroxy Acids, Bionic Acids, Retinoic Acid and Vitamin C as additional members. (More info: Ingredient Spotlight Vitamin C and Ingredient Spotlight Retinol) You probably know most of those as beneficial for the skin already, so it shouldn’t be surprising that PHA show positive effects in skincare as well.
The group they are associated the closest with are the Alpha-Hydroxy Acids, with the difference that Polyhydroxy Acids, with Poly meaning many, have multiple hydroxy groups, which makes them a bigger molecule.
The most common ones found in skincare are Gluconolactone, Galactose and Lactobionic Acid, which just like Glycolic Acid are water soluble as opposed to the oil-soluble Salicylic Acid.
To my knowledge there has never been a study that compared the different PHA side by side, so it probably doesn’t depend which exact one is in the products you are using, and I have also found very different concentrations used in studies and products without a clear determination which one is superior. While The Inkey List PHA Toner for example features 3% PHA, in a comparing study both 10% and 30% were used split face without a significant difference in effectiveness. The general consensus seems to be that if you stay below the 10% range, you will most likely not experience any issues, and that the combination of ingredients is much more important than the percentage when it comes to how they work on your skin.
To be fair, most brands don’t list the percentage at all or say the product contains 10% of PHA+AHA, so giving you a concentration wouldn’t help much anyway.


Two of the PHA most commonly used in skincare
Two of the PHA most commonly used in skincare


The benefits of using PHA in skincare

Being closely related to AHA, PHA show the same benefits: They exfoliate by breaking up the bonds that glue the superficial layer of dead skin cells together, which means they smooth the skin. They also show good effects in brightening hyperpigmentation and sun damage, especially when combined with other ingredients and they seem to increase the production of Glycosaminoglycans and collagen fibers, leading to plumper and firmer skin. (More info: What is hyperpigmentation and how do I treat it?)

In a nutshell, they help reverse signs of premature aging, and that was demonstrated on African American, Caucasian, Hispanic and Asian skin.
Due to their larger structure they won’t penetrate as deeply as the smaller Glycolic Acid will, being more effective on the surface level of the skin and minimizing the risk of irritation.

More benefits that seem to be exclusive to PHA is their ability to act as antioxidants, their ability to act as humectants due to their multiple hydroxy groups and their ability to bind to the metalloproteinase enzyme that is responsible for degrading collagen and that way slow collagen breakdown.

In a study that compared Gluconolactone and Glycolic Acid in their effect on premature aging as in fine lines, mottled pigmentation, texture, firmness and pore size found them to be equally as effective over a period of 12 weeks with Glycolic Acid only being superior in improving skin firmness and sallowness, while Gluconolactone showed less stinging, burning and sensitivity. This is just one study though, so the topic needs further investigation.


The side effects of using PHA on your skin

As I mentioned before, PHA are usually well tolerated due to their larger size and minimal depth of penetration. There is no such thing as a fool-proof ingredient though, meaning that you can of course overdo them and experience redness, stinging and other signs of irritation, especially when using high concentrations and in combination with other potentially irritating ingredients like prescription acne treatment.
While PHA have been successfully paired with 15% Azelaic Acid in rosacea patients, with Tretinoin in acne patients and with Glycolic Acid peels done in office, so in high concentrations, I always recommend to start slowly and reevaluate regularly, ideally with the help of your treating doctor, if you need all the actives combined in your routine. Remember: the less you use, the less can cause you trouble! (More info: How to use Retin A with minimal irritation)
With that out of the way: I personally have had no issues using The Inkey List PHA Toner for several weeks combined with my Tretinoin and occasional Salicylic Acid, and I would consider my skin to be on the more reactive side when it comes to acids.


Who will benefit the most from introducing PHA into their skincare routine?

With the benefits similar to those of Alpha Hydroxy Acids and a simultaneously lower risk of irritation, the short answer would be: anyone that can’t tolerate AHAs due to sensitive skin or accompanying treatments while aiming to fight signs of premature aging.
Now not everyone needs a Glycolic Acid, if your main concern is blocked pores for example, you are probably better off looking for Salicylic Acid. Other people using a strong retinoid don’t feel the need to exfoliate at all – remember, skincare is always individual to you, there is no need to use an acid because everyone says so!
Those with hyperpigmentation issues though, those with rosacea that want to incorporate a well-aging regime or those with dry patches that want both help with the texture and with the hydration might find them beneficial.
And if you are a person of color that struggles with photodamage, but also is prone to postinflammatory hyperpigmentation after irritation, PHAs might be the better choice for you.


The Inkey List PHA Toner
The Inkey List PHA Toner


Products with PHA for you to try

Now that one first: I only ever tried one dedicated PHA product, the aforementioned PHA toner from The Inkey List (100 ml for 10,99 €, full review here). Short info though: It is great, non-irritating, affordable, but didn’t deliver drastic results. That doesn’t mean it didn’t do anything, it is just that if you use the gentler option, you will need to wait longer until you see results, and if your skincare is already pretty good like mine, I doubt that you will ever see drastic results with any new product. It is one that I would recommend though.


Zelens PHA+ Resurfacing Facial Pads
Zelens PHA+ Resurfacing Facial Pads

The other product I personally have tried is a mix product: The Zelens PHA+ Resurfacing Facial Pads (150 ml for 74 €) that contain Lactobionic Acid, Salicylic Acid, Citric and Lactic Acid alongside Niacinamide and Postbiotics and that offer a slightly stronger, yet still very well tolerable exfoliation on my skin. (More info: Everything you need to know about Niacinamide and Everything you need to know about Pre-, Pro- and postbiotics)
More mix products that come highly recommended, but that I have personally not tried myself is the Glossier Solution (130 ml for 24 $) that uses a mix of Alpha Hydroxy Acids, Salicylic Acid and Polyhydrox Acid with a total of 10% acids in the formula, and the Peter Ole Henriksen PHAT Glow Facial (50 ml for 47,95 €) – see what they did with the name there? PHAt? – which combines Gluconolactone with Kaolin Clay. An interesting combination indeed, especially if your skin is more on the oily side.

Many products like moisturizers might contain PHA as well without stating that on the label. Because, circling back to my introduction, they aren’t as new as one might think. They simply haven’t taken the spotlight beforehand. So it is indeed worth checking if the moisturizer you are already using does contain some Gluconolactone before you rush out to buy a dedicated product.


What is the role of Polyhydroxy Acids (PHA) in skincare?
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