Sara Hammad
Upon feeling thirsty , we easily drink water. In hot weather, we can have a refreshing bath, dip into a sea or a swimming pool. When it rains, we enjoy this scene and go play with water falling on our faces wetting our clothes.
What if the previous scenario is your worst nightmare?! What if your own tears is blistering your skin? Can you imagine your own sweat leaving a trail of red, itchy hives behind ? Unfortunately, this is the case with aquagenic urticaria (water urticaria or water allergy).
Aquagenic urticaria (AU) was first described by Shelley and Rawnsley in 1964. It is a rare form of physical urticaria with only 50 cases have been reported worldwide. Any contact with water – even your own tears – triggers a painful, swollen and intensively itching rash within 20-30 min of exposure.
This reaction occurs regardless of temperature, purity or salt content of water, even chemical-free and many-times distilled water will set it off. The rash mostly develops on the face, neck, trunk and upper limbs.
The peak incidence is with the onset of puberty with female predominance. Most cases are sporadic, but familial and hereditary predisposition have been reported. Thank god that water within our cells is not the problem, otherwise we would wonder how this happens and 60% of the human body is water!
You are probably wondering what might cause such a bizzare reaction to water? Well, the exact cause of water allergy is still unknown. However, there are several hypothesis to describe it. Shelley and Rawnsley hypothesized that water interacts with sebum or sebaceous glands, producing toxic substances that stimulate peri-follicular mast cell degranulation with the release of histamine.
Czarnetzki et al. proposed the existence of a water-soluble antigen in the epidermal layer, which diffuses into the dermis via water, resulting in histamine release from mast cells. Tkach proposed that a sudden change in osmotic pressure around hair follicles results in indirect provocation of urticaria. Luong and Nguyen in 1998 suggested that the mechanism is independent of histamine release as histamine level of several patients was normal during the attack. Pretreatment with scopolamine (an acetylcholine antagonist) before water contact suppressed wheal formation which indeed supports Luong and Nguyen theory.
Patients are diagnosed with aquagenic urticaria based on history, results of a water provocation test and histopathologic examination. The standard method is water provocation test in which the clinician uses a towel soaked in tap water at body temperature. It is performed on on patient's skin (arm or trunk).
Pruritus, multiple small wheals with surrounding erythema is observed on the water-exposed area after 5 minutes of exposure.Diagnosis is confirmed by conducting Laboratory tests and Histopathologic examinations. Indeed, there are several questions to be asked here like 'How do they survive without water? And how water urticaria is handled?'
As an answer for the first question, AU patients limit themselves to shower once a week. To minimize sweating, they wear light clothes, avoid exercise and drink milk instead of water.
The main treatment for water urticaria is long-acting antihistamines. Topical treatment of skin can be also effective where it acts as a barrier to water contact.
Ultraviolet (UV) radiation is a suggested therapy for resistant cases. The point of using it is that applying UV rays to skin induces epidermal thickening. Consequently, decreases water penetration and the activity of mast cells to allergens in the water. It has also been found that removal of stratum corneum enhances whealing, while application of petrolatum ointment prevents it. After all, we have to admit that people with AU live an alternate aquagenic reality. They have to stay at home when it rains to not experience the symptoms of allergy. They wake up every single day with wheals and edema.
While drinking water for a normal individual feels pleasurable, for AU patients it feels like a glass of stinging nettles. Certainly, It is a different kind of suffer. There still a question that comes to mind which is "What about their kidneys ? How it can tolerate this very limited water intake?"
Many questions need to be answered by scientists and researchers in the near future and hopefully we will find new and creative solutions.
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