Vascular changes in human skin after ultraviolet irradiation.

Blood-flow changes in human skin after ultraviolet irradiation at 250 and 300 nm have been measured by three separate methods. Those methods which measure overall blood-flow changes in the skin showed increased flow after irradiation at both wavelengths. A method which measured flow only in the superficial vessels showed a slight increase in flow after low doses of both wavelengths, but in contrast, after higher doses, this method showed a marked reduction in flow through the upper dermal vessels. This reduction in flow is probably due to stasis in these superficial vessels, perhaps secondary to vascular damage. Contrary to previous reports, blood-flow changes after irradiation at 250 and 300 nm are similar and may be mediated by identical mechanisms.