Years ago, exfoliating was something of an act of aggression, accomplished via buff puff, intense peel, retinoid, or coarse scrub. The thinking was that if it thoroughly polished, burned, or made you peel like a snake, a glowy visage was surely just around the corner. Thanks to backlash from skin experts and brands (ahem) alike, though, we’ve become a bit more considerate when it comes to getting rid of dead skin cells. Enter lactic acid.
What is lactic acid?
Lactic acid is a type of alpha hydroxy acid that can be naturally derived from milk or fermented plants. Unlike a scrub or microdermabrasion treatment—both physical exfoliants that manually buff away dead skin—alpha hydroxy acids are chemical exfoliants that work by “dissolving the bonds between skin cells, allowing dead cells to slough off,” explains Sonia Batra M.D., a board-certified dermatologist and co-host of The Doctors television show.
The reason it’s so gentle
There are a handful of alpha hydroxy acids, but lactic and glycolic acids are the most common. Notably, the former has been shown to be the less irritating—but equally effective—of the two: “Because lactic acid has a larger molecular size than other AHAs, it doesn’t penetrate as deeply and the exfoliation isn’t as intense,” explains Los Angeles-based shamanic facialist Julie Civiello Polier. AHAs like lactic acid are also easier on skin than beta hydroxy acids like salicylic acid, which have a smaller molecular size that penetrates and exfoliates deeper. Additionally, lactic acid is easier on skin because of its moisturizing properties: Research has demonstrated that it increases ceramides, the lipids in our skin barrier. This improves barrier function, preventing irritation.
Its strong-but-soft reputation matters: Batra says that aggressive exfoliation can lead to irritation, micro tears, redness, and “portals of entry for bacteria” in your skin barrier. That’s why Civiello Polier tells her clients to exfoliate no more than twice a week. In the case of acids, opt for a wash-off treatment, like the Resurfacing Moisture Mask, instead of a leave-on treatment. (Generally, the longer an acid is on skin, the more likely it is to cause irritation.)
Lactic acid’s other skin benefits
Beyond being moisturizing and gentle, lactic acid is also incredibly revitalizing. “When you remove that outer layer of dull, dead skin, it reveals a fresher layer underneath,” Batra explains. That even surface also reflects more light—which is why you look more luminous right away.
On top of the immediate improvements, regular exfoliation boosts cell turnover—something that naturally slows down over time. “Many of my patients are frustrated because their skin doesn’t glow the way it used to,” Batra says. “As we age we’re holding onto that dull outer layer of skin longer.” Faster cell turnover has a number of trickle-down effects over time, from increased collagen production to brightened hyperpigmentation to improved skin quality overall (think generally bouncier, softer, more youthful skin). What’s more, exfoliation helps keep skin clear, since dead skin cells aren’t lingering on the surface and clogging pores.
There are full-body advantages to boot. It’s the go-to active for treating keratosis pilaris, the tiny chicken skin-like bumps that can appear on limbs, and, in low concentrations, can be used to nix the flakes that come with eczema and psoriasis, Batra says. And it brings the same smoothing, softening, and firming benefits to the arms and legs that it does the face. That’s why Cleopatra, the original beauty influencer, is said to have bathed regularly in lactic acid-rich milk. For a more modern version, try a body peel, like the Resurfacing Body Mask. It leaves skin looking radiant and feeling silky—and it’s dairy-free.