MNN Galleries

10 extremely unusual allergies

shower head

Photo: stevendepolo/Flickr

2 of 12

Water

It seems like the most innocuous substance around, but believe it or not, some people are actually allergic to water. Aquagenic urticaria is a rare condition in which water of any temperature causes intensely itchy and painful hives on the skin. An effective treatment hasn't been found, making regular activities — like showering and swimming — extremely difficult.