21 CFR § 701.20 - Detergent substances, other than soap, intended for use in cleansing the body.
(a) In its definition of the term cosmetic, the Federal Food, Drug, and Cosmetic Act specifically excludes soap. The term soap is nowhere defined in the act. In administering the act, the Food and Drug Administration interprets the term “soap” to apply only to articles that meet the following conditions:
(1) The bulk of the nonvolatile matter in the product consists of an alkali salt of fatty acids and the detergent properties of the article are due to the alkali-fatty acid compounds; and
(2) The product is labeled, sold, and represented only as soap.
(b) Products intended for cleansing the human body and which are not “soap” as set out in paragraph (a) of this section are “cosmetics,” and accordingly they are subject to the requirements of the act and the regulations thereunder. For example, such a product in bar form is subject to the requirement, among others, that it shall bear a label containing an accurate statement of the weight of the bar in avoirdupois pounds and ounces, this statement to be prominently and conspicuously displayed so as to be likely to be read under the customary conditions of purchase and use.