In 1885 Paul Unna the elder proposed to ameliorate the occasional deleterious effects of soap on the skin by using more fat than was required to neutralize the alkali employed in its manufacture. This superfat, it was reasoned, would eliminate the possibility of free alkali remaining in the finished soap and might even combine with the alkali formed by hydrolysis when the soap was dissolved in water.
The concept that the irritating and drying actions of soaps on the skin are dependent only on their alkaline reaction is no longer held. Soaps of fatty acids with a short carbon chain (i. e., low molecular weight), which hydrolyze least1 and are therefore least alkaline, have been found to be most irritating to the skin.2 Also in this connection, Bleyberg and Lettner3 have concluded that the presence in soap of a few tenths of 1 per cent of free
KILE RL. CLINICAL EVALUATION OF A SUPERFATTED SOAP. Arch Derm Syphilol. 1942;45(2):377–381. doi:10.1001/archderm.1942.01500080121013
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