You think a peanut allergy is bad? Try being allergic to water.
Despite being called a water allergy, it’s not exactly a true allergy to water. I mean, we need water to live and on average we’re 53% water (48% if you’re female, 58% if you’re male). It would be pretty tough if contact with water was enough to send someone into anaphylactic shock. But people with aquagenic urticaria do not like to get wet.
For these people, skin contact with water causes them to break out in welts or hives for up to an hour. A similar condition, aquagenic pruritus, produces a strong itchy sensation but no welts. We don’t know exactly why this happens – is it the water itself, or is it something in the water that triggers these reactions? Well, aquagenic urticaria is triggered even by pure distilled water, so if it’s something else it’s pretty persistent.
This is the thing that I find particularly tough about this condition: it’s not just rain, baths, and showers that can trigger it. Your own body moisture can set off the same effect. Imagine being allergic to your own spit, tears, and sweat. It would put quite a crimp on your love life, ability to watch romantic films, and exercise routine respectively.
There is a kind of urticaria that is triggered just by sweat (cholinergic urticaria) but this is much worse. You’d have to put petroleum jelly on your body just to have a bath. These conditions are fortunately extremely rare, much like solar urticaria – a mild sun allergy.