What is it?
An alpha hydroxy acid (AHA) that occurs naturally in foods and is made commercially by fermenting carbohydrates or by chemical synthesis. In cosmetics it has two roles. In small amounts it adjusts a product’s pH and helps hold moisture. At higher strengths and lower pH it works as an exfoliant, loosening the bonds between dead cells on the skin’s surface. It is also a common food acid, listed as E270.
Key information
- Lactic acid is an alpha hydroxy acid (AHA) that occurs naturally in foods and is made commercially by fermentation or synthesis.
- The CIR Expert Panel found it safe in consumer cosmetics at up to 10 percent and a pH of 3.5 or higher, when products avoid increasing sun sensitivity or tell users to protect their skin from the sun daily.
- Like other exfoliating AHAs, it can sting and irritate, and pH is the biggest factor in how irritating it is.
- The FDA advises using sun protection while using AHA products and for a week afterward.
More information
The Cosmetic Ingredient Review (CIR) Expert Panel reviewed glycolic and lactic acids, with their common salts and simple esters, in the late 1990s. It concluded they are safe in consumer products at concentrations of 10 percent or less and a final pH of 3.5 or higher, when formulated to avoid increasing sun sensitivity or when directions call for daily sun protection. Salon peels were considered safe at up to 30 percent and pH 3.0 or higher, for brief use by trained professionals followed by thorough rinsing.
The acidity that lets lactic acid exfoliate is also what makes it sting. The EU’s former cosmetics safety committee (SCCNFP) noted in 2000 that pH is the most important factor in how irritating an AHA is. In FDA-sponsored studies, which used glycolic acid, four weeks of AHA use increased volunteers’ sensitivity to UV reddening by 18 percent and roughly doubled UV-induced cell damage, with no significant difference a week after stopping. The FDA recommends a “Sunburn Alert” on AHA products and sun protection during use and for a week afterward. On a precautionary basis, the SCCNFP suggested a lower limit for lactic acid, 2.5 percent at pH 5 or higher, until more data were available. Health Canada restricts AHAs in cosmetics with concentration and pH conditions and warnings, including avoiding the eyes and stopping use if irritation persists.
Reality check: lactic acid occurs naturally in foods, and the FDA affirms it as generally recognized as safe (GRAS) as a food ingredient. In many products it appears in small amounts to set the pH. The cautions above apply mainly to exfoliating products, especially peels and low-pH leave-on treatments. If a product is sold for exfoliation, follow its sun-protection directions.
On labels it appears as lactic acid, often alongside its salt, sodium lactate.
Sources: FDA: Alpha hydroxy acids; European Commission SCCNFP: Position paper concerning the safety of alpha-hydroxy acids (2000); Health Canada: Cosmetic Ingredient Hotlist, prohibited and restricted ingredients; Code of Federal Regulations, 21 CFR 184.1061 (via Cornell LII): Lactic acid
