4. Photosensitization

This is a skin pathological mechanism following UV exposure, due to photochemical modifications, by UV rays, of substances absorbed locally in the skin or reaching the skin surface via circulating blood. These modified substances become allergens by combining with blood proteins.

Photosensitization leads to allergic type IV skin reactions, with erythema, edema, thickening of the epidermis and hyperpigmentation.

In appearance, these skin reactions may be mistaken for sunburn. The diagnosis can only be made by questioning the victim.

Here's an example of some substances known to be photoallergenic: sulfonamides, phenothiazines, tribromosalicyclanilide (depigmentation).