Other names you’ll find on cosmetic labels: Specially Denatured (SD) Alcohol 3-A, SD Alcohol 30, SD Alcohol 39, SD Alcohol 39-B, SD Alcohol 39-C, SD Alcohol 40, SD Alcohol 40-B, SD Alcohol 40-C.

What it is: Ethanol that has been denatured (made undrinkable, toxic, and/or dyed).

Purpose in cosmetics:  astringent, anti-foaming agent, solvent and to decrease viscosity.

Other popular uses: common ingredient in shellac & shellac based products, also used to lift stains, kill bugs, and is a common fuel for camp stoves.

There’s a long list of ingredients that can be used to denature alcohol, including (but not limited to) acetone (flammable/nail polish remover/paint thinner), isopropyl alcohol (flammable/sterilizer/[1] defatting agent), methanol (flammable/highly toxic), Brucine (plant extract/alkaloid/poisonous).

Which chemical is used to denature your product of choice is really anyone’s guess, as labeling laws don’t require the manufacturer to list the compounds of each ingredient.  Regardless of wether or not your product of choice lists the denaturalizer,  you are still putting ethanol (fuel!) on your skin.