All living creatures are dependent on water to live. When it comes to humans, our brains and hearts are composed of around 70 percent water, while our lungs contain a whopping 80 percent - even our bones are about 30 percent water. To survive, we need close to 2.4 litres daily on average, some of which we get from food.

But what happens if you're allergic to water? That's the case for a rare few, who have a condition called aquagenic urticaria. American teen, Alexandra Allen, was diagnosed with aquagenic urticaria in 2013 - her allergy to water means she has to limit her cleaning rituals to 5-minute cold showers twice a week, cut her hair short and became a vegetarian in order for her body to produce less oil.

"I'm told that someday, my throat might swell when I drink water, but if there's one thing I've learned since getting this, it's that we all have things to deal with in life," she told People magazine in April. People with the condition restrict their eating of certain fruits and vegetables with high water content, and often opt for drinking diet soft-drinks instead of tea, coffee, or juice.

As well as watching one's diet, a person living with aquagenic urticaria has to keep a number of natural biological factors in check, such as sweat and tears, plus keep their exposure to rain and humid conditions to a minimum to avoid hives, swelling, and pain. As you can imagine, controlling emotional reactions - no tears! - and the effects of exercise is a tremendous challenge.

The first recorded case of aquagenic urticaria was documented in 1963, when a 15-year-old girl broke out in sores after water-skiing. It was subsequently defined as a severe sensitivity to water, manifested by itchy hives breaking out on the exposed skin within minutes.

The condition appears to be more common in women, and is likely to develop during puberty, with a genetic disposition being the most likely cause. Its rarity means it's often misdiagnosed as an allergy to chemicals in water, such as chlorine or salt. Inflammation can last for an hour or longer and can lead to patients developing a phobia of bathing in water. Severe cases can result in anaphylactic shock.

In the medical literature, there are less than a hundred case studies, with research focusing on the condition's relation to other serious conditions such as T-cell non-Hodgkin’s lymphoma and hepatitis C infections. The lack of research into treatment and diagnosis has made the identification of the condition difficult, but antihistamines have proven to work for some people. Fortunately, it does seem that the condition wanes in severity as the patient gets older.

One of the ways of dealing with the condition is self-management and emotional support, Allen told New York Magazine. "I'm hoping that by talking about this weird disease, maybe it will help the next 12-year-old who freaks out because she learns she can't be a mermaid."