The effect of vitamin A acid on experimentally induced comedones: an electron microscope study.

Various concentrations of vitamin A acid were applied to experimentally induced comedones. All concentrations produced non-cohesive hyperkeratinization, which loosened the cohesive horny mass induced by oleic acid and expelled it from the follicle within 7 days. The highest concentration (0.1%) produced the greatest degree of non-cohesive desquamation in the shortest time. In follicles treated with the acid, the cell membrane of horny cells was thin and ruptured easily to produce a non-cohesive debris. Desmosomes were scarce and desmosomal bodies (fusiform electron-dense bodies) and tight junctions between horny cells were not seen in follicles treated with the acid. The acid also produced hyperplasia of the epithelial wall and an apparently increased mitotic rate. A 0.025% concentration of the acid increased the number of membrane coating granules by about 70% in all regions of the follicle.