Aquagenic urticaria

The exact underlying cause of aquagenic urticaria is poorly understood. However, scientists have proposed the following theories:

• A substance dissolved in water enters the skin and triggers an immune response. In this theory, the hives are not caused by water, specifically, but rather an allergen in the water.
• An interaction between water and a substance found in or on the skin generates a toxic material, which leads to the development of hives.

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.

Most cases of aquagenic urticaria seem to occur sporadically in people with no family history of aquagenic urticaria. However, familial cases have been reported on several occasions, with one report describing the disease in three generations of a single family. Some familial cases have been reported in association with other conditions, some of which can be familial. In other words, the family members who had aquagenic urticaria also had another potentially inherited medical condition. However, to our knowledge, no specific inheritance pattern has been definitively associated with aquagenic urticaria.

Due to the rarity of aquagenic urticaria (AU), there is very limited data regarding the effectiveness of individual treatments. To date, no large-scale studies have been conducted. Unlike other types of physical urticaria where one can avoid the agent that causes the hives, avoidance of water is not practical. The following treatments (alone or in various combinations) have been used to manage or treat AU with variable results:

• Antihistamines – These typically are used as the first-line medical therapy for all forms of urticaria. Those that block H1 receptors (H1 antihistamines) and are non-sedating, such as cetirizine, are preferred. Other H1 antihistamines (such as hydroxyzine) or H2 antihistamines (such as cimetidine) may be tried if H1 antihistamines are not effective.
• Creams or other topical agents that serve as a barrier between water and the skin, such as petrolatum-based products. These may be used prior to bathing or other exposure to water to prevent water penetration into the skin.
• Ultraviolet light therapy (also called phototherapy), such as Psoralens ultraviolet radiation A (PUVA) and ultraviolet radiation B, have been reported to resolve symptoms of AU in a few cases.
• Omalizumab – an injectable medication typically used for people with severe asthma. This medication has reportedly been tried successfully in a few people with AU.

Due to the lack of strong evidence of the safety and effectiveness of the treatments mentioned above for people with AU specifically, those with AU should consult with their doctors regarding personal treatment options. Some people with AU may not experience improvement of symptoms with medical treatment and may need to rely on minimizing water exposure by limiting bathing time and avoiding water-based activities.