Popular brands of soaps and shampoos were assayed for comedogenicity in the rabbit ear. Only a small number produced hyperkeratosis when applied at a 25% concentration. Bacteriostatic substances, especially hexachlorophene, were mildly comedogenic. Conventional soaps include salts of fatty acids; the latter are known comedogens.
The obsessive use of soaps by patients with acne vulgaris may aggravate the disease and result in its extension to unusual locations.
Mills OH, Kligman AM. Acne Detergicans. Arch Dermatol. 1975;111(1):65-68. doi:10.1001/archderm.1975.01630130067007