Background: Solar urticaria is a rare photosensitivity disorder characterized by the rapid onset of a pruritic, erythematous and urticarial rash following sun-exposure. The action spectrum and degree of photosensitivity have been observed to change over time in several isolated reports.
Methods: Monochromator phototesting was performed on multiple occasions on 12 patients with solar urticaria.
Results: Six patients demonstrated normal responses in the initial phototest. They remained normal in five patients upon subsequent testing. Seven patients demonstrated abnormal immediate responses, most frequently at UVA wavelengths. Within some individuals, variations in action spectrum and/or degree of photosensitivity were observed over the years, but not over days.
Conclusion: Significant changes in action spectrum and degree of photosensitivity may occur over years in solar urticaria. However, changes over shorter periods of time are likely to be minor and not have clinical significance.