Ultrastructural Changes Induced by Ultraviolet Light in Human Epidermis: Basal and Spinous Layers.

Cytoplasmic alterations in human epidermis irradiated with ultraviolet light have been described by light microscopy (1, 2). Pronounced changes occurred in cells of the basal and spinous layers at the peak of the erythema reaction (twenty-four to thirty hours after irradiation). At this time, cells in the spinous layer developed homogeneous, deeply staining cytoplasm and pyknosis of nuclei. Tbe cytoplasm of some cells became vacuolated and small intraepidermal vesicles formed. Exocytosis was reported in the study of Rost and Keller (1). No observable changes occurred in epidermis when biopsy specimens were taken in the early phase (5 hours post-irradiation) of erythema (1). Mieseher (3, 4) emphasized that cellular effects of ultraviolet irradiation depended in part upon the intensity of irradiation. At low intensity only the upper cellular layers developed vacuolation of cytoplasm and pyknosis of nuclei, whereas high intensity irradiation effected changes at deeper levels or even resulted in epidermal necrosis. Cells of the basal layer showed no cytoplasmie homogenization or nuclear pyknosis; but, in the earlier investigation (1), this layer exhibited varying degrees of intraand intercellular edema. Accumulation of PAS-positive granules in epidermal basal cells occurred after ultraviolet irradiation and the amount of PAS material seemed to be directly proportional to the degree of erythema (2). Increased epidermal mitotic activity has been reported from ultraviolet irradiation (2, 3). We wish to report post-irradiation events observed at the ultrastruetural level.