The effect of vitamin A on epidermal dynamics is complicated by many variables, including species and regional differences, which render compilation of meaningful data difficult. Available evidence indicates that vitamin A has a predominantly proliferative effect on mature rodent and human epidermis, which may be dose-dependent. The ancient concept of an "antikeratinizing effect" is thus incomplete, though possibly not incorrect, when applied to mammalian epidermis. Mucous metaplasia in response to excess vitamin A, though consistently seen in embryonic chicken skin, is not a feature of the mammalian response, except in specific epithelia with "mucoid potential." The precise mode of action at the molecular level remains unknown, but lysosomal labilization may be of major importance.
Logan WS. Vitamin A and Keratinization. Arch Dermatol. 1972;105(5):748-753. doi:10.1001/archderm.1972.01620080072021