Photoallergic contact dermatitis to Heracleum giganteum.

Heracleum plants occur in numerous species worldwide and may cause phototoxic reactions due to its content of various furocoumarins. In this case report, a widespread photoallergic contact dermatitis after exposure to Heracleum giganteum (giant bear claw) is described. A photopatch test with extracts from the stem, leaves and seeds of the giant bear claw revealed a positive papulovesicular reaction that already appeared at 24 h and peaked at 72 h after irradiation with 5 J/cm(2) UVA. The unirradiated controls remained negative. We conclude that in rare cases Heracleum plants may cause severe photoallergic reactions that can be verified by photopatch testing.