A case of localized heat urticaria in a 70-year-old woman is reported. Increased plasma levels of prostaglandin D2 and blood histamine after heat challenge indicate a role for mast cell degranulation in the pathophysiology of the syndrome. Treatment with astemizole increased the temperature threshold to wealing, but not to itch or erythema. The patient was partially desensitized by repeated exposure to heat and this was further improved by indomethacin. After treatment there was no increase in plasma prostaglandin D2 on challenge. No evidence was found for the activation of the alternative complement pathway.

Seven patients, four female and three male, who develop intense pruritus without visible skin changes in light‐exposed areas after sun exposure are reviewed. Onset in all cases has been in childhood or adolescence and the condition has persisted indefinitely except in one patient who has been in remission‐for I year and one who was in remission for 5 years before relapse. Itching occurs on sun‐exposed areas within 45 min to 24 h and lasts for 1–5 days. No patient has taken photosensitizing medications or suffered from any significant systemic illness. There is a positive family history of polymorphic light eruption (PLE) in one, and of sunlight‐induced pruritus in another. Porphyrin studies and antinuclear factor titres are normal. Cutaneous phototesting of the back by monochromator is normal in the UV‐B, UV‐A and visible light ranges. Irradiation from a xenon arc solar simulator in one patient induced intense pruritus with no visible skin changes on the tested sites of the anterior forearm and back in a time course mimicking that of sun‐induced symptoms. Treatment by sun avoidance, topical sunscreens and antihistamines has been only partially effective. Two patients have subsequently developed occasional typical PLE upon sun exposure, but sun‐induced pruritus alone occurs most frequently. This suggests that polymorphic light eruption sine eruptione is a variant of PLE and, to our knowledge, is the first report of this condition.