Water is the essential element that all life forms have in common. It’s the basis of our cells, and it composes the bulk of our mass. It’s so essential to life that even a week without water intake can result in death—not just in humans, but in animals and plants of all kinds. But surprisingly, there are people who are allergic to water. It’s an extremely rare allergy, but it has been documented. How exactly does this work, and how to water-allergic people deal with it?

Also known as aquagenic urticarial, water allergy has been documented in a variety of medical journals. This rare reaction leads to intense burning and itchiness all over the skin, and it can happen after just minimal contact with water—or even as a result of one’s own sweat.

If this sounds a little terrifying, take comfort in the fact that there have only been around 40 cases documented for as long as medical records have been kept. And because it’s so rare, we haven’t fully figured out the mechanism behind it. However, it’s thought to result from a hypersensitivity to the ions, minerals, and chemicals found within water. After all, all water—even water that’s been designated “pure”—contains much more than just h2o, and these extra elements are likely what causes water allergy.

The presence of other chemicals may help explain why allergic reactions to water most commonly result from exposure to water from the tap. One of the most prominent cases of aquagenic urticarial was found in an Australian teenage girl; after having an abnormal reaction to a heavy dose of penicillin, she developed a water allergy. Now, even just a small drop of water makes her break out in painful welts and itchy hives all over her body.

Unfortunately, there is still no cure for water allergy, which is why people with the disorder must take great pains to avoid water exposure. And obviously, because they can’t drink standard water, the condition has profound effects on their lives. In some cases, regular intake of anti-allergy medications can alleviate the condition, but there is still no complete cure.