The location of the proliferative pool of cells in normal epidermis, ichthyosis vulgaris, lamellar ichthyosis, X-linked ichthyosis, epidermolytic hyperkeratosis, and psoriasis was examined using autoradiographic and projection techniques.
A significant number of thymidine-labeled cells (deoxyribonucleic acid-synthesizing cells) were found above the basal cell layer in all conditions examined. Cell proliferation in the epidermis is not limited to the basal layer but also occurs in more superficial cells.
Penneys NS, Fulton JE, Weinstein GD, Frost P. Location of Proliferating Cells in Human Epidermis. Arch Dermatol. 1970;101(3):323-327. doi:10.1001/archderm.1970.04000030067010