Phytophotodermatitis is caused by the combined influence of sunlight and psoralen (8-methoxypsoralen, 5-methoxypsoralen) found in certain plants. The skin eruption is reddish and stinging and may even be vesicular. The reaction is not allergic but occurs in any person who on a sweaty summer day comes into skin contact with the fluid contained in e.g. the burning bush or giant weed like the hogweed or (wild) angelica and is then exposed to sunlight. The dark pigment marks may remain for years.