Polymorphous light eruption occurs in approximately 10 to 20 percent[3] of otherwise healthy individuals, so it is a relatively common condition.

[2] Secondary photodermatoses stems from underlying disorders including genetic diseases and photoaggravated dermatoses.

The medical professional takes into consideration the time since sun exposure; use of creams/makeup, medications, and contact with plants; frequency of pruritis; improvements with less exposure to sun such as during winter months; and family history of photodermatoses.

Physical examinations look for signs of erythematous rashes and swelling of areas exposed to sun, including face, upper neck or back, and primary skin lesions which includes vesicle and blisters.

Challenge-rechallenge testing is done by withdrawing and reintroducing the suspected cause and checking for reaction.