Phytophotodermatitis.

Several plant families contain species liable to cause phytophotodermatitis. They include the Umbelliferae of which Ammi majus has been known for centuries and the Rutacea to which Citrus bergamia belongs. Phototoxic plants are also found in, e.g., the Moraceae, Leguminosae, Rosaceae and Compositae plant families. The photoreactivity of the plants depends on their furocoumarins (psoralens) content. These cause skin damage by phototoxic mechanisms, when activated by longwave ultraviolet radiation (UVA). The results are clinical changes such as erythema, bullae in the skin 24-72 h later, followed by hyperpigmentation. For the strongest phototoxic plants the content of the major phototoxic furocoumarins like bergapten or xanthotoxin have been calculated at approximately 0.5 g/100 g dried plant weight, but it varies between plant parts and also with the age of the plant. Repeated contact may occasionally lead to photocontact allergy.