In chemistry, an alcohol is any compound that contains one or more hydroxyl (-OH) groups attached to a (possibly substituted) hydrocarbon backbone. In common usage, the term "alcohol" often refers specifically to ethanol (C2H5OH), but this is not always the case. For example rubbing alcohol is typically iso-propanol (C3H7OH), which is much more toxic than ethanol. Methanol (CH3OH) and ethylene glycol (anti-freeze, C2H4(OH)2) are particularly toxic, and can readily cause blindness (in the case of methanol) or death. Not all alcohols are intoxicating - for example, glycerol (C3H5(OH)3), a component of fats, is not.