It has long been observed that sun exposure can induce or exacerbate skin l
esions in patients with certain forms of lupus erythematosus. Despite the f
requency of photosensitivity in these patients, the mechanism by which ultr
aviolet radiation alters the pathogenic course of this disease remains poor
ly understood. After development of standardized test methods, our group de
monstrated in 1986 that skin lesions in patients with lupus erythematosus c
an be experimentally reproduced by UVA and UVB irradiation. In the followin
g years, phototesting has received much attention as a valid model to study
photosensitivity of different forms of lupus erythematosus and the pathoge
netic mechanism of this disease. Further investigations have also made it p
ossible to find genetic and immunologic factors associated with photosensit
ivity and have helped to identify the pathophysiologic steps involved in th
e induction of such skin lesions. We present prototesting results and clini
cal correlations of more than 400 patients with different forms of lupus er
ythematosus and discuss the recent advances in provocative phototesting.