Polyhydroxy acids (PHAs) are having a major skincare moment. Considered second-generation alpha-hydroxy acids (AHAs), PHAs work in a similar way. They break down and remove the “glue” that binds dead cells to the skin surface, revealing a brighter, plumper and smoother complexion. AHAs, beta-hydroxy acids (BHAs) and PHAs form the triumvirate of chemical skin exfoliants. 

The gentler exfoliant 
The most common PHAs are gluconolactone, galactose and lactobionic acid. As they have larger molecules than AHAs, they can’t penetrate skin as deeply, so their work is confined to the top layer, sloughing away dull, dead cells as slower-acting but equally effective exfoliants. If you find AHAs too harsh, PHAs might work for you – they are clinically proven to be suitable for sensitive skin.  

PHAs are actually not that new. Clinical studies from as far back as 2004 have detailed their use in treating photodamaged skin. Says dermatologist Dr Teo Wan Lin: “PHAs seem novel because the term ‘polyhydroxy acid’ hasn’t been used frequently in recent times, although our knowledge of it stems from the 1970s.” 

The reason we’ve seen a slew of PHA products in recent months is down to business. The patent on PHAs recently expired, so the cost of using it as an ingredient in skincare products has been drastically lowered.

Over-the-counter skincare is probably where you’ll find PHAs, rather than at your dermatologist’s office. “The depth of penetration and effectiveness of PHAs in chemical peels may be less than what you get with AHAs and BHAs,” says Dr Teo. “In skincare, however, the medical literature seems to report that it is a much gentler and more moisturising chemical exfoliant than the other acids, which translates to a lower risk of skin irritation.”

Better skin benefits  

Aside from exfoliating, PHAs help the skin in other ways. For one, they don’t increase its sensitivity to the sun, a big downside of AHAs. For another, they are said to have an anti-sagging effect. PHAs have the unique ability to fight glycation, a process in which digested sugar attaches itself to collagen in skin and weakens it, making elastin levels plummet, eventually leading to sagging.  

As humectants, PHAs also attract and bind water to skin, keeping it hydrated. While these humectant properties are not as impressive as those of hyaluronic acid, they give sensitive skin another layer of protection against irritation. 

PHAs also render excess iron in skin inactive. Too much of the trace metal speeds up skin ageing, and the hydroxy acids help ensure the extra iron can’t do any damage. 

Gluconolactone, one of the most common forms of PHA, has the additional benefit of renewing skin cells at a faster rate, while galactose speeds up wound healing.

Who should use it?

If you’re used to a routine of hard-hitting, fast-acting exfoliating acids, the slow and steady PHA approach may not be for you. 

The beauty of PHAs lies in their gentle nature. They can be used by people with rosacea, eczema and other sensitivity issues that keep them from exfoliating. It takes more time – two to three weeks – to see more radiant skin, compared with almost immediately when AHAs are used.  

Dr Sylvia Ramirez, an epidemiologist and the medical and scientific director of Cutis Medical Laser Clinics, says: “Since they don’t penetrate skin deeply, consider using PHA products that stay on your skin, like a moisturiser or a serum. This is especially helpful for dry skin, as they can retain water and provide additional hydration.”

Dr Ramirez adds that you can combine AHA- and BHA-based products with PHA ones. Just alternate them: Use one in the morning, the other at night. “A clinical study has proven that using a topical cream with PHA can improve the skin’s radiance when combined with AHA cleansers and sunscreen,” she adds.

That said, no matter how gentle PHAs are, they are exfoliators, so you should still exercise caution to minimise skin irritation when introducing them to your beauty routine. “Although PHAs are gentler than other chemical peels, you should still take precautions if you have sensitive or compromised skin,” says Dr Ramirez.  

If your skin tends to react to new products, build up its barrier with ceramides, hyaluronic acid and antioxidants before using chemical exfoliants. Also, if you’re pregnant, breastfeeding, or have open wounds on your face or a skin infection, you may not tolerate gluconolactone or lactobionic acid as well, says Dr Ramirez. If you’re unsure, consult a dermatologist

Below, some products with PHA that you can try: