When Alexandra Allen was 12, she did what most kids do when they're on a family vacation: She went for a swim in the hotel pool. Unlike most kids, though, Alexandra had a severe reaction to her swim. Her skin broke out in angry, itchy welts just a few short hours after leaving the water.
What began as an ordinary summer day ended in an eventual diagnosis that would change Allen's life. She shelved her dreams of living on a sailboat and working as a marine biologist after discovering she was allergic to water [source: Neporent].
An allergy to water seems like an improbable condition. After all, water is a chief chemical component in the human body, accounting for at least 60 percent of the average person's weight. Water whisks toxins out of critical organs, ferries nutrients to hungry cells and creates the humid conditions needed for ear, nose and throat health. In short, water is essential to life [source: Mayo Clinic].
In the case of water allergies, only the skin is affected. People with this condition can still safely drink water. It's only when water of any temperature or origin touches the skin that a hypersensitive allergic reaction occurs.
The condition, known as aquagenic urticaria, is called an "allergy" but isn't medically classified as a true allergy. It's actually an allergy-like reaction that belongs to a subset of physical urticaria, a group of conditions characterized by hives or welts that arise from stimulation of the skin.
In the case of aquagenic urticaria, red, swollen, itchy bumps form when water touches the skin. This histamine reaction isn't directed at the water itself, but is most likely a reaction to a water-soluble antigen that stimulates antibodies. Any type of water — distilled, tap or rain — will cause an outbreak almost immediately and can make bathing or getting caught outside in a rainstorm a torturous proposition.
Aquagenic urticaria is so rare that fewer than 100 occurrences have been recorded in medical literature since the first cases were described in 1964. It affects women more than men and most often begins in puberty. It's usually diagnosed by putting the skin into prolonged contact with water. In Allen's case, physicians asked her to soak in a tub of water to diagnose the condition.
The cause of water "allergies" still eludes experts. One theory is that sweat glands could be the culprit. It's possible that sweat glands in certain people produce a toxin that leads to an allergic reaction with water.
While researchers remain unsure of the root cause of the condition, most cases can be treated with antihistamines and controlled by avoiding contact with water as much as possible.