Alcohol denat.

What it is

Ethanol plus denaturants, such as denatonium benzoate, which tastes bitter at 10 parts per billion. The Cosmetic Ingredient Review panel reviewed it in 2008 and decided safety should be judged on the denaturants, because normal cosmetic use does not produce meaningful systemic ethanol exposure. CIR 2008

How it works

It evaporates fast, dissolves styling polymers and fragrance, and acts as a penetration enhancer on skin. CIR 2008 We found no study measuring ethanol-containing products on hair dryness or breakage, so the belief that "alcohol dries out hair" is plausible but untested at cosmetic exposure. Dryness on the scalp, rather than in the fibre, is the more likely practical effect (reasoned).

What the studies show

• Safety review only, with no hair-effect trials. Patch tests of products containing high levels of SD alcohol 40 (one hair product had 47%) showed no sensitisation or phototoxicity. CIR 2008

Side effects and safety

Ethanol is a reproductive and developmental toxicant when swallowed, and the panel notes that products have been consumed intentionally and by accident. It is flammable. CIR 2008

Bottom line

Not a reason to avoid a product on its own. In a hair spray it is doing its job. Dry, curly, damaged or scalp-sensitive users may prefer lower-alcohol styling products, and alcohol denat. high on the ingredient list of a leave-in tonic is the main case for caution. We are fairly sure about safety and not sure about dryness.