Potential hazards in phototherapy with ultraviolet radiation arising from variation in dose required to produce erythema.

Phototherapy using 290-320 nm ultraviolet radiation (ultraviolet B) is an effective form of treatment for several skin diseases and is especially useful for psoriasis. Technical advances have made it more economical and convenient to quantify ultraviolet radiation. Ten volunteers received a series of exposures from three ultraviolet B sources to illustrate how variation in the spectral properties of phototherapy devices can lead to unanticipated and potentially severe sunburn reactions. The corresponding minimal erythema dose was then calculated with the use of irradiance data measured with two commercially available photometers. Variation in minimal erythema dose among the three sources tested indicates the need to characterize the emission spectrum of sources and the spectral sensitivity of the photometer used to measure its output.