For such a mysterious illness, the hunt for a cure has been suitably bewildering. At the moment, the standard treatment is to take powerful anti-histamines. To understand why, first we need to get to grips with what goes down during a reaction.

It all kicks off when immune cells in the skin, known as mast cells, release inflammatory histamine proteins. During a normal immune reaction, histamines are extremely helpful – making blood vessels leaky enough to allow white blood cells through to attack any intruders. During a reaction to water, all you get are the side-effects: fluid seeps out through their walls, causing the surrounding skin to swell up.

At the same time, histamine activates “itch neurons”, whose only role is to make us want to itch. The result is a patch of raised, itchy areas of skin known as welts.

In theory, anti-histamines should work every time. In practice, the drugs have decidedly mixed results.

Back in 2014, Rachel was sent to the ECARF in Berlin as part of a documentary, where doctors suggested she try a high dose. She did as they said – then put them to the test at her local swimming pool. It didn’t work. “Afterwards I was itching like crazy and I looked like I was diseased,” she says.

For years, anti-histamines were the only option. Then in 2008 Maurer and colleagues from the ECARF had an idea. “We didn’t evolve mast cells so that we could suffer from urticaria. So what gets them to do bad things?” he says.

The histamine-releasing cells of people with the condition look entirely normal, and they don’t have any more than the rest of us. So something else must be telling them to act up. From studies in the lab, the scientists thought the culprit might be IgE, the antibody responsible for true allergies, such as those to pollen or cats.

“Instead of reacting to something from the outside world, they’re producing IgE in response to something within themselves,” says Maurer.

All they needed was a drug which could block IgE’s effects. And as luck would have it, there was already a drug on the market which could do just that.

Omalizumab was originally developed as a treatment for asthma. “When we said ‘we’d like to use this anti-allergic drug in these patients’ the drug company said ‘why would you want to do that? It’s not an allergy, how can that work,’” says Maurer.

After convincing the sceptics, in August 2009 they put the idea to the test. Their patient was a 48-year old woman with another rare form of urticaria, which is triggered by pressure. For three years, the patient had been breaking out into a raised, itchy rash at slightest touch. It was so bad, it would happen when she combed her hair or dressed.

After just a week of treatment, the woman’s symptoms were visibly diminished. By the end of the month, they had completely disappeared.

Since then scientists have discovered omalizumab is effective against even the most obscure forms of urticaria – from reactions to sunlight to changes in temperature, to friction. “It’s amazing; I mean this drug is a complete game-changer,” says Maurer.