Water urticaria, or aquagenic urticaria, is a rare condition in which hives develop within 1 to 15 minutes after contact with water. The hives last for 10 to 120 minutes and do not seem to be caused by histamine release like the other physical hives. Most investigators believe that this condition is actually exquisite skin sensitivity to additives in the water such as chlorine.
Water urticaria is diagnosed by applying tap water and distilled water to the skin and observing the reaction.
Water urticaria is treated with a cream called capsaicin (Zostrix) that is applied to the irritated skin. This is the same treatment used for shingles. Antihistamines are of questionable benefit since histamine is not the causative factor in water urticaria.