All you need to know about PHA.

Regarded as the next generation of hydroxyl acids, the PHAs (polyhydroxy acids) stand apart from AHAs (alpha-hydroxy acids) and BHAs (beta-hydroxy acids) by their distinctive chemical structure: they are carboxylic acids bearing two or more hydroxyl (–OH) groups attached to carbon atoms or to a cyclic aliphatic chain, whereas AHAs and BHAs carry only one. Moreover, unlike AHAs, PHAs are larger molecules, which limits their penetration into the epidermis. Their action is therefore more superficial yet also gentler.

The three main PHAs used in cosmetics are:

• Gluconolactone (or gluconic acid): Naturally present in skin cells, gluconolactone is the most popular polyhydroxy acid. In addition to its exfoliating properties, it offers antioxidant activity and anti-inflammatory effects, making it beneficial for redness-prone skin.

• Galactose: This simple sugar is naturally present in the body. In cosmetics, it is prized for its exfoliating benefits as well as its ability to stimulate the regeneration of skin tissue.

• Lactobionic acid: Derived from the oxidation of lactose, it belongs to the subcategory of polyhydroxylated bionic acids (PHBA). Its distinctive sugar-enriched chemical structure renders it a potent humectant: it attracts and retains water in the skin, thus enhancing epidermal hydration.

The polyhydroxy acids are versatile actives that can be used on both the skin and the scalp. They possess a combination of exfoliating, hydrating, soothing, and antioxidant properties, which explains their growing success in cosmetics.

• PHAs exhibit a mild keratolytic effect.

  Like AHAs, PHAs exert a keratolytic action, but in a more gradual and better-tolerated manner. They dissolve the bonds between corneocytes, thereby facilitating the shedding of dead cells that accumulate on the skin’s surface. This process of chemical exfoliation refines skin texture, reduces pore congestion, and limits the formation of blackheads. By stimulating cell turnover, PHAs also help diminish the appearance of fine lines and fight dull complexion, caused by a buildup of dead cells on the face that prevents light from reflecting evenly.

• PHAs are moisturizing.

  Unlike AHAs and BHAs, PHAs possess multiple hydroxyl groups that give them strong hygroscopic properties. They attract water in the skin and retain it within the epidermis, helping restore hydration and improve skin elasticity. This ability to limit dehydration explains why polyhydroxy acids are particularly effective for exfoliating dry skin.

  Clinical studies have confirmed this property. In 16 women with dry skin, the effect of applying a formulation containing 10% gluconolactone was evaluated using corneometric measurements. After two weeks of use, a significant increase in skin hydration was observed, as shown in the table below.

• PHAs are thought to possess anti-inflammatory properties.

  Several studies suggest that PHAs also exhibit anti-inflammatory activity. By reducing the production of pro-inflammatory mediators, they may help limit redness and irritation. This property, still under investigation, complements the exfoliating action of PHAs in caring for acne-prone skin.

• PHAs have antioxidant properties.

  PHAs can also protect the skin against oxidative stress. Indeed, their chemical structure, which is rich in hydroxyl groups, allows them to chelate free radicals, unstable molecules that attack cellular components. By neutralizing these reactive species, PHAs help shield the skin from environmental aggressors such as pollution and UV radiation. This antioxidant effect also contributes to slowing down the processes associated with skin aging.

• PHAs protect the skin against photoaging.

  Beyond the antioxidant action of polyhydroxy acids, some studies have highlighted their potential to protect the skin against UV-induced alterations. For example, gluconolactone, applied at 7.5%, has demonstrated in vitro the capacity to reduce UV-induced elastin promoter activation by 50%, while not promoting the formation of so-called “sunburn” cells, which indicate UV-related structural damage.

  In addition, a clinical study involving the topical application of a cream containing 8% lactobionic acid for 12 weeks demonstrated, through histological analysis, a significant reduction in the expression of matrix metalloproteinase 9 (MMP-9), an enzyme that degrades elastin and contributes to skin laxity. These findings suggest that PHAs not only prevent oxidative damage but also help preserve the dermal extracellular matrix and mitigate photoaging.

PHAs are considered safe and well tolerated, even for sensitive skin.

Their distinctive feature lies in their larger molecular size compared to AHAs and BHAs. This structure limits their ability to penetrate deeply into the epidermis, thereby reducing the risk of irritation, stinging, or excessive peeling. That is why polyhydroxy acids represent a particularly interesting alternative for exfoliating sensitive skin. Moreover, unlike AHAs and BHAs, PHAs are not photosensitizing. They can therefore be used without issue in summer or in the morning, but this obviously does not replace the need to apply a sunscreen. Additionally, PHAs can be used during pregnancy or while breastfeeding.

That said, even though these are gentle active ingredients, some people may be sensitive to them and develop slight redness upon contact. Therefore, as a precaution, as with any new active ingredient, we recommend performing a tolerance test on first use. To do this, apply a small amount of product to the inside of your arm and observe the area for 24 hours. In the absence of any reaction (redness, itching, irritation), you can safely proceed with application to your face or scalp.

PHAs are most commonly found in exfoliating serums, toning lotions, cleansing gels, and facial masks. Typology has developed three products incorporating gluconolactone:

• The exfoliating face gel cleanser : With 5% gluconolactone and aloe vera, this formula is made up of 98% naturally derived ingredients. It unclogs pores, evens out skin tone, and smooths skin texture. It is particularly recommended for dull complexions and those prone to blackheads.

• The mask for enlarged pores and blackheads : It combines a 10% AHA complex (glycolic acid, lactic acid, tartaric acid, mandelic acid) and 10% PHA (gluconolactone) to act at different depths of the epidermis and remove dead skin cells. It is used in the evening, once or twice a week, and helps even out skin tone and smooth skin texture.

• The mark-fading serum : Enriched with 14% PHA and also containing Centella asiatica, this serum works to fade acne scars. It should be applied topically to the affected areas, in the evening only.

• The scalp scrub : It is an exfoliating gel to use before shampooing that gently removes dead skin cells for a healthy, rebalanced scalp. It delivers dual chemical and mechanical exfoliation thanks to gluconolactone and jojoba beads.

• BARNETSON R. & al. A comparative study of gluconolactone versus benzoyl peroxide in the treatment of acne. Australasian Journal of Dermatology (1992).

• KSENZENKO S. M. & al. The polyhydroxy acid gluconolactone protects against ultraviolet radiation in an in vitro model of cutaneous photoaging. Dermatologic Surgery  (2004).

• EDISON B. L. & al. The use of polyhydroxy acids (PHAs) in photoaged skin. Cutis (2004).

• VAN SCOTT E. J. & al. Clinical and cosmeceutical uses of hydroxyacids. Clinics in Dermatology (2009).

• HEARING V. J. & al. Applications of hydroxy acids: classification, mechanisms, and photoactivity. Clinical, Cosmetic and Investigational Dermatology (2010).

• ROTSZTEJN H. & al. Lactic and lactobionic acids as typically moisturizing compounds. International Journal of Dermatology (2019).

• ROTSZTEJN H. & al. Corneometric evaluation of skin moisture after application of 10% and 30% gluconolactone. Skin Research and Technology (2021).