Glycolic acid is a crystalline solid that is colorless, odorless, and highly hygroscopic. Numerous skin-care products contain it due to its exfoliating properties. In nature, glycolic acid occurs frequently. It is an alpha hydroxy acid (AHA), which has two components that are only one carbon apart: a carboxylic acid part (HO =0) and a hydroxy group (-OH).
Origin
There are several ways to synthesize glycolic acid. Because it is inexpensive, the most common methods use a catalyzed reaction of formaldehyde with a hydrogen and carbon monoxide mixture (carbonylation of formaldehyde). It can also be made by mixing sodium hydroxide and chloroacetic acid, then re-acidifying the result. Other techniques, which are hardly ever used today, include formaldehyde-derived cyanohydrin hydrolysis and oxalic acid hydrogenation. Some of the glycolic acids used today don't contain formic acid. Natural sources of glycolic acid include sugarcane, sugar beets, pineapple, cantaloupe, and unripe grapes.
Safety profile
The Cosmetic Ingredient Review (CIR) published their findings on the safety of glycolic acid and recommended that cosmetic products contain no more than 10.0% w/w glycolic acid and its derivatives and that the pH of any product be greater than 3.5. Furthermore, salon products should contain no more than 30.0% w/w glycolic acid and its derivatives, and the pH of any product should be greater than 3.0.
The Food and Drugs Administration (FDA) recommended that the labeling of a cosmetic product that contains an AHA as an ingredient and that is topically applied to the skin or mucous membrane, bear a statement that conveys the following information:
Sunburn Alert: This product contains an alpha hydroxy acid (AHA) that may increase your skin's sensitivity to the sun and particularly the possibility of sunburn. Use a sunscreen, wear protective clothing, and limit sun exposure while using this product and for a week afterwards.
The European Union Scientific Committee on Cosmetic Products and Non-Food Products Intended for Consumers (SCCNFP), stated that glycolic acid may be used safely at levels up to 4% and pH ≥ 3.8; it was also recommended that contact with eyes be avoided and that UV protection be used when using cosmetic products containing AHAs.