In section 701.20 of Title 21 of the Code of Federal Regulations [21 CFR 701.20], the Food and Drug Administration (FDA) defines the term "soap" as a product in which the non-volatile portion consists principally of an alkali salt of fatty acids, i.e., the traditional composition of soap; the product is labeled as soap; and the label statements refer only to cleansing. If cosmetic claims, e.g., moisturizing, deodorizing, skin softening etc., are made on a label, the product is a cosmetic. Synthetic detergent bars are also considered cosmetics, although they may be labeled as "soap." Taken from http://www.cfsan.fda.gov/~dms/cos-lab3.html#clgi