A diagnosis of aquagenic urticaria is typically suspected based on the presence of characteristic signs and symptoms . A "water challenge test" may then be ordered to confirm the diagnosis. During this test, a compress of 35ºC water is applied to the upper body for 30 minutes.The upper body is chosen as the preferred site for the test because other areas, such as the legs, are affected less commonly. It is important to tell the patient to not have any antihistamines for several days before the test.In some case reports, rinsing specific areas of the body with water or giving a direct bath and shower challenges has been attempted. Use of these tests may be needed when the usual water challenge test using a small water compress is negative, although it should be avoided in patients who have a history of serious symptoms.