I first read about PHAs a few years back when I was looking for gentler chemical exfoliants for my rosacean skin. As with many people who have atopic dermatitis, acne, or rosacea, traditional glycolic acid (and even the gentler forms of AHA such as lactic acid or mandelic acid) can be rough. It stings, burns, and can cause aggressive flare-ups of redness that domino into other reactions. With rosacean skin specifically, I referred to this as “status cosmeticus” or cosmetic intolerance syndrome. Unfortunately, those with delicate skin still find themselves needing a form of exfoliation. This is where PHAs can be helpful.
There are lots of claims about PHA floating around the Internet, so to break all of the noise down into a short list, the key claims of PHAs are:
- Less irritating
- Humectant (water-binding properties)
- Photoaging benefits comparable to AHAs
- Not sun sensitizing
Note: Several studies that I found around PHAs were sponsored by Neostrata, a skincare company that uses PHAs as a flagship ingredient. This does not mean that these studies are not valuable, as many studies done by private companies are very useful, but it is worth disclosing.
There are two main types of polyhydroxy acids (PHAs): Gluconolactone and Lactobionic Acid.
Gluconolactone is a derivative of gluconic acid, an organic compound found in mammals that breaks down carbohydrates. It is frequently produced from corn and is most often used as an exfoliant, though it sometimes moonlights in your ingredient lists as a preservative. It’s sister, lactobionic acid, is a sugar acid and is formed from gluconic acid and galactose, a monosaccharide.
There are several places online that consider PHAs to be just as effective as AHAs but without all of the irritation of AHAs. This is largely due to it’s greater molecular weight.
Molecular weight is a factor that comes up frequently when considering the efficacy and irritation potential of a product. I’ve even mentioned it before when discussing various types of “gentler” AHAs such as mandelic acid and lactic acid.
To be able to determine whether an ingredient or compound can penetrate the skin, the “500 Dalton rule” is referenced most frequently, which states that compounds of molecular weights equal to or below 500 Daltons can pass transcutaneously. The following is a chart of the various weights of the three most popular AHAs against the two most common forms of PHA with water as a point of reference:
|Molecular Weight of AHAs vs PHAs|
|Glycolic Acid (AHA)||76|
|Lactic Acid (AHA)||90|
|Mandelic Acid (AHA)||152|
|Lactobionic Acid (PHA)||358|
The 500 Dalton rule is why some ingredients – such as the collagen in your anti-aging cream – are more of a marketing ploy than actually beneficial to the “anti-aging” of your skin.
This irritation due to the lower or higher molecular weights can be felt almost immediately by some people, typically in the form of redness or stinging. In such cases, higher molecular weighted ingredients (such as PHAs) are preferable. In one small, twelve-week, controlled-use study, Caucasian women with mild to moderate facial photodamage were enrolled in a study that compared PHAs (n=30) to AHAs (n=27). At the end of the study, “irritation grading and subject self-assessment showed that the PHA regimen was better tolerated than the AHA regimen. Stinging and burning were significantly worse for subjects in the AHA treatment group at both week 6 and week 12, and degree of sensitivity was rated worse for the AHA regimen as well.” (Source)
PHAs are also highly humectant, particularly lactobionic acid, which may be calming to irritated skin and weakened skin barriers. One study that outlined the various types of hydroxy acids states the following about BAs (bionic acids such as lactobionic acid):
BAs are hygroscopic materials that readily attract and retain water, forming a gel matrix when their aqueous solution is evaporated at room temperature. The transparent gel contains certain amounts of water, forming a clear gel matrix. Formation of a gel matrix may add protective and soothing effects for inflamed skin. Indeed, formulations containing BA are well tolerated and help calm skin when applied after cosmetic procedures that weaken the skin’s barrier, including superficial HA peels and microdermabrasion. (Source)
Another study found that this water-loving property may be particularly valuable for those with rosacea who are using azelaic acid (AzA). In a 12-week, single-site, investigator-blinded, randomized, Neostrata-sponsored study of 66 patients with mild-to-moderate type 2 rosacea:
Improvements were seen in skin sensitivity, dryness, texture, smoothness, and overall skin condition with statistical significance (p<0.05) in the patients using the dermatologist-recommended regimen (Group 2) compared to those using their own self-selected regimen (Group 1). …
Draelos also noted an appreciable clinical improvement in background erythema in patients using the dermatologist-selected regimen and postulates that this improvement in background erythema may be a result of improved SC function from the gluconolactone in the formula. Gluconolactone is a PHA that exhibits humectant properties, which can improve SC barrier function temporarily by inducing a swelling of corneocytes as discussed previously. (Source)
As with all things and rosacea, your mileage may vary. Rosacean skin is extremely sensitive and many may find PHAs to still be too irritating for their skin. Patch testing is advised.
In addition to usage with AzA, PHAs can be formulated and used in conjunction with oxidative drugs such as benzoyl peroxide (BP) “to help reduce irritation potential and erythema [redness] caused by the oxidative drug.” (Source)
PHAs have also proven useful at preventing skin irritation and reducing trans-epidermal water loss (TEWL). One study compared four different types of hydroxy acids (glycolic, lactic, tartaric, and gluconolactone) with skin barrier function and irritation. After four weeks, a 5% sodium lauryl sulphate (SLS) patch test was performed. The gluconolactone-treated sites showed “significantly lower TEWL” at both 24 and 48 hours after the patch test was performed. (Source)
The percentage of acid content in PHA products seems to matter little when comparing the hydration levels in the skin. A small study (n=10) compared the effects of a 10% lactobionic acid (LA) peel to 30% LA peel in a split-face test. They concluded no noticeable differences in the participants hydration levels. (Source)
PHAs are also touted as having “anti-aging” benefits, specifically improving the appearance of the skin. One Neostrata-sponsored study comparing PHAs to AHAs that I referenced above concluded a “relative equivalence of AHAs and PHAs in treating photoaged skin … both regimens provided significant antiaging benefits to skin as measured by clinical evaluations…”
PHAs can also prove valuable in boosting the dermis-thickening benefits of tretinoin, thus reducing fine lines and wrinkles. According to one journal:
In summary, PHA-containing products were used in combination with retinoic acid in treating adult facial acne and were found to be well tolerated. PHAs plus retinyl acetate (pro-vitamin A) in a cream base exhibited significant antiaging skin benefits such as skin smoothing and plumping. … Finally, PHA-containing products were shown to be compatible with African American, Caucasian, and Hispanic/Asian skin and provided significant improvements in photoaging in these populations. (Source)
This is consistent with findings in vitro and in vivo showing the increased production of collagen, hyaluronic acid, and fibroblasts in the dermis due to extended periods of application of glycolic acid.
PHAs may also improve the effects of hydroquinone and assist in reversing hyperpigmentation and photoaging. One example:
Adult man with hyperpigmentation and photoaging at (left) baseline and (right) after twice-daily use of an α-hydroxyacid (AHA)/polyhydroxy acid (PHA)/bionic acid (BA) skin care regimen for 12 weeks. Use of the skin care products resulted in significantly less hyperpigmentation and improved radiance. The product regimen included: 20% AHA/BA cleanser, 10% PHA/BA SPF 15 cream for daytime use, and 15% AHA lotion for nighttime use. (Source)
It is also worth noting that PHAs, particularly gluconolactone, do not increase sun sensitization, making them a good choice for those who are unable to use sunscreen but are still looking for some form of chemical exfoliation.
… an in vitro [test performed outside of the body] cutaneous model of photoaging demonstrated that gluconolactone protects against ultraviolet (UV) radiation. These findings were attributed to the ability of gluconolactone to chelate oxidation-promoting metals and trap free radicals. In addition, pretreatment of skin with gluconolactone does not lead to an increase in sunburn cells after UVB irradiation, as has been shown to occur with glycolic acid; this is thought to be due to its antioxidant effects. (Source)
Just as with AHA, PHA must be formulated at the proper pH in order to be effective. Similar to glycolic acid, the effective pH of PHA is 3.8. The lower the pH value (the more acidic), the more free acid is available to exfoliate the skin, meaning that formulation is important.
When purchasing a PHA, look for a leave-on product as opposed to a wash-off product, which will give it more time to activate on the skin. Products that are already formulated with combination therapies may also be valuable to reduce the number of steps in your routine as well as ensure there are no ingredients that can interfere with the penetration or efficacy of the active ingredients (such as PHA).
If you use tretinoin (Retin-A), adapalene (Differin), or tazarotene (Tazorac), you may also want to space out your product usage, using PHAs during the day and your retinoid at night. As with anything though, do what is best for your unique skin type.
Do you use a PHA product? If so, what are your favorites? Let me know in the comments below!