How FDA defines "soap"
Not every product marketed as soap meets FDA's definition of the term. FDA interprets the term "soap" to apply only when --
The bulk of the nonvolatile matter in the product consists of an alkali salt of fatty acids and the product's detergent properties are due to the alkali-fatty acid compounds, and
The product is labeled, sold, and represented solely as soap [21 CFR 701.20].
If a cleanser does not meet all of these criteria...
If a product intended to cleanse the human body does not meet all the criteria for soap, as listed above, it is either a cosmetic or a drug. For example:
If a product --
consists of detergents or
primarily of alkali salts of fatty acids and
is intended not only for cleansing but also for other cosmetic uses, such as beautifying or moisturizing,
it is regulated as a cosmetic.
If a product --
consists of detergents or
primarily of alkali salts of fatty acids and
is intended not only for cleansing but also to cure, treat, or prevent disease or to affect the structure or any function of the human body,
it is regulated as a drug.
If a product --
is intended solely for cleansing the human body and
has the characteristics consumers generally associate with soap,
does not consist primarily of alkali salts of fatty acids,
it may be identified in labeling as soap, but it is regulated as a cosmetic.