Aquagenic urticaria (water allergy): symptoms, causes and management

Urticaria, or hives, is a rash of itchy raised weals. The NHS notes that triggers can include food, medicines, infections, scratching or pressure, cold, heat and even water or sunlight, although the last two are rare. Most hives have no single trigger that can be pinned down, but a smaller group are inducible: they are brought on reliably by a specific physical stimulus.

Aquagenic urticaria sits in that group. BAD lists it alongside symptomatic dermographism, cold, solar, cholinergic and delayed pressure urticaria, and notes that the weals usually appear within minutes and last for less than one hour. It describes the water-induced form as extremely rare, with small weals occurring at the site of contact with water, usually on the upper part of the body.

Patient.info, a UK health information site whose article was peer reviewed by an NHS GP, adds that fewer than 100 cases have been reported in the medical literature and that it appears to affect more women than men.

People describe an itchy, stinging or prickling rash of small raised red bumps that appears within minutes of water touching the skin and fades over roughly half an hour to an hour once the skin is dry. Patient.info says symptoms tend to go away in 30 to 60 minutes.

The trunk and upper body are most often involved. The trigger can be the shower, a bath, rain, sweat or tears, which makes everyday life hard to plan around. The reaction is local to the skin that has been in contact, so it is different from the generalised swelling of anaphylaxis, although severe reactions are possible in principle and your doctor will advise on emergency medicine if there is any history of breathing difficulty.

• Itchy, small raised weals or red bumps after contact with water.

• Onset within minutes; fading usually within an hour.

• Rash mainly on the upper body, though it can appear anywhere water touches.

• Triggers that include showers, baths, swimming, rain, sweat and tears.

• Symptoms that do not depend on how warm or cool the water is.

The cause is not understood. Patient.info says the condition is as poorly understood as it is rare, and describes two popular theories. The first is that, rather than the water itself, it may be chemicals in the water that act as allergens and trigger the release of histamine. The second is that the water interacts with the skin's natural oils, known as sebum.

These are hypotheses rather than established mechanisms. What is clear from BAD is that the reaction is a form of urticaria, in which skin mast cells release histamine and other chemicals, producing itch and weals.

Diagnosis begins with a careful history of when the rash appears and what has touched the skin. A GP will usually want to rule out the more common causes of itching, and may refer to a dermatologist or an allergy clinic. BAD notes that tests for autoimmune urticaria are not routinely available and generally do not alter treatment, so diagnosis rests largely on the story and the examination.

In specialist centres a clinician may apply a water-soaked cloth to the skin under controlled conditions to see whether weals appear. This distinguishes aquagenic urticaria from other conditions that can look similar, such as aquagenic pruritus, where there is itch without weals, or cholinergic urticaria, where sweating or a rise in body temperature is the trigger. Photographs of the rash taken on a phone are very helpful because weals fade within an hour.

Patient.info states that there is no cure for being allergic to water, so the aim is to limit exposure where practicable and take allergy treatments. The NHS says a pharmacist can advise on antihistamine treatment for hives, that some people cannot take antihistamines because of other conditions, and that a GP might prescribe antihistamines, menthol cream or steroid tablets.

Patient.info observes that completely avoiding water is not possible, but small adaptations help: shorter showers with a quick towel-down, patting rather than rubbing the skin, pre-treating the skin before swimming or bathing if your doctor agrees, checking the weather before going out and having a change of clothes to hand.

Because the condition is so unusual, many people feel isolated. Talking to a GP about the effect on sleep, work and mood is worthwhile, and psychological support can be offered if the impact is significant. Charities that support people with allergy and skin conditions can provide information, even if they have limited material on this specific condition.

The NHS says to call 999 if your lips, mouth, throat or tongue suddenly become swollen, you are breathing very fast or struggling to breathe, your throat feels tight or you struggle to swallow, your skin turns blue, grey or pale, or you become suddenly confused, drowsy or dizzy. Anyone who has been prescribed an adrenaline auto-injector should use it as instructed and call 999.

Hives that last longer than a few hours, are very painful, leave bruising or are accompanied by fever or joint pain should be reviewed by a GP, because they may represent a different type of urticaria.

On the NHS, a GP can start antihistamines and refer to dermatology or allergy services if the diagnosis is uncertain or treatment fails. Some specialist tests and injections such as omalizumab are given in hospital clinics.

Private dermatologists and allergists can offer an earlier appointment and challenge testing. Because the condition is so rare, it can be useful to ask whether the clinician has seen water-induced urticaria before, and to keep records of what has and has not helped.