Photoallergic reaction. Classification and pathogenesis.

In the present article, an attempt was made to classify photoallergic reactions. Theoretically, they can be divided into four types, based on the origin of photoallergens and on the type of allergy. The photoallergen may be endogenous or exogenous in origin and photoallergic reaction may be immediate or delayed in nature. Lichen planus-like photosensitivity reaction was classified as another type of photoallergy because clinical features are distinct from the other four types. Pathogenic mechanisms were also discussed in each type of reaction, reviewing experimental evidences and speculative concepts of my own and other investigators.