An unusual, but well-recognized non-IgE-mediated, food-related cause of urticaria is histamine poisoning, which occurs if food containing a very high content of histamine is eaten. The best-known example is ‘scombroid poisoning’ which is due to ingestion of scombroid fish (spiny-finned fish of the mackerel genus), such as tuna, mackerel and swordfish, which has not been stored properly and in which bacteria have decarboxylated histidine to produce histamine. (Ingestion of spoiled non-scombroid fish including herring, sardines and anchovies may also cause histamine poisoning.) Symptoms usually begin within 1 h of ingestion of the fish and patients develop urticaria and gastrointestinal symptoms. In severe cases there may be bronchospasm and hypotension. Physical factors such as cold, heat, sweating, exercise, pressure, sunlight, water and vibration may all trigger urticarial reactions. The weals of physical urticarias tend to be short-lived (less than an hour), apart from those of delayed pressure urticaria, which develop over a few hours and may take up to 2 days to disappear. International standards for diagnosing physical urticarias have been proposed.