Used to make cosmetics "pretty," synthetic colors, along with synthetic hair dyes, should be avoided at all costs. For US products they will be labelled as FD&C (Food, Drugs & Cosmetics, in reference to the US Federal Act) or D&C, followed by a colour and a number. Example: FD&C Red No. 6 / D&C Green No. 6. In Europe they are referred to using E numbers .