Polymorphic light eruption

Sometimes known as prickly heat, this consists of very itchy urticarial papules and plaques usually arising 24 hours after exposure to the sun. Often it is induced by UVA (in this case a sun bed) and total sun blocks containing titanium dioxide are required to block it. It persists for several days before subsiding and recurs with the next exposure. It does not respond well to antihistamines but does to systemic steroids, which also may be used prophylactically. Chloroquine and photochemotherapy (PUVA) are also used but neither is without risk. Prevention with protective clothing, appropriate sun blocks and sun avoidance is the wisest course.