Acids for the sensitive
Coming from someone who has allergies to almost everything (I did a panel at an allergist's office--it was bad) and reacts to half of the stuff I put on my skin, I am always on the lookout for something that can be powerful and gentle at the same time. Thankfully, my skin doesn't react terribly to certain AHA and BHA products, but I've seen a new-ish crop of products filtering into the beauty market: PHAs, or polyhydroxy acids. They were discovered in the 70s and have been in a number of beauty products, but just aren't as ubiquitous as their alpha- and beta-counterparts.
PHAs are not exactly an entirely different category of acids either. They are a group of "new generation" alpha-hydroxy acids. Compositionally, PHAs have more hydroxyl groups (thus the name) and the addition of more of these groups provide humectant-like hydration to the skin. They draw in water externally and from within the skin. They also promote a gentle exfoliating effect on the skin but do not penetrate as deeply as AHAs, and therefore don't end up being as irritating on the skin. An AHA like glycolic acid will disrupt calcium ion channels in the skin cells, causing them to separate. This is how the exfoliation occurs. A BHA like salicylic acid will soften keratin and cause greater skin turnover while also breaking down desmosomes, the attachments between outer layer skin cells. This is the main pore unclogging mechanism. Lipohydroxy acid is another, newer BHA that exfoliates by evenly manipulating membrane adhesion between cells.
Clinical studies have shown that PHAs, like gluconolactone, provide anti-aging effects on skin (greater skin thickness and firmness) much like AHAs but are less irritating. PHAs were also more tolerated towards the later stages of the study as subjects in the AHA group were found to have more irritated skin. In addition to the anti-aging benefits they deliver, PHAs improve skin barrier function and contain antioxidant properties. Another study showed that PHAs in conjunction with hydroquinone (a depigmentation compound) led to subjects having brighter skin and lightened pigmentation. PHAs with retinol showed even better anti-aging effects. Further, 14% PHA solutions work just as well as 5% benzoyl peroxide without the irritation for the treatment of mild to moderate acne.
You can incorporate PHAs into your routine in any number of ways. Remember to always give your skin time for the acid to absorb and work. This means waiting a couple of minutes after application before putting on another product. NeoStrata Facial Cleanser is a gentle everyday formula that contains gluconolactone. It works as a gentle daily exfoliator without stripping your skin of moisture. If your skin needs a daily scrub this is a good one to try. Skinfood Freshmade Pineapple Mask has a mild peeling effect that still leaves the skin hydrated. It can be used after cleansing and washed off. Zelens PHA+ Bio Peel Pads are a great way to exfoliate after cleansing. You can leave it on or rinse off after 5 minutes. Cosrx PHA Moisture Renewal Power Cream can be used as a mask (left overnight or rinsed off after 10 minutes) or as a moisturizer. It has 3% PHA and tons of coconut fruit extract for moisture. Exuviance Evening Restorative Complex contains PHA and vitamins A, C, and E to improve skin tone and texture while reducing fine lines and wrinkles.