Abstract
In tissue culture trunk skin from 8-day-old chick embryos showed a consistent change from keratinizing into more columnar non-keratinizing epithelium under the influence of vitamin A acid using concentrations from 10 to 20 IU/ml. Human adult postauricular and ear canal skin, cholesteatoma membrane, and human embryonic skin retained their keratinizing properties when exposed to vitamin A acid at concentrations up to 150 IU/ml, when toxic changes in the epithelium became obvious. Treatment of cholesteatoma ears with vitamin A ear drops is unlikely to effect any change in the keratinizing properties of the epithelium.