A) It’s very rare
B) It’s not an allergy in that it doesn’t cause a histamine release*, like your allergy to flowers or an allergy to shrimp that causes the throat to close up
C) We’re not entirely sure what it is
and
D) Yes, it’s real
I’m not sure why she thinks she can drink only Coke; that part seems to be hysterics in action. Aquagenic urticaria (assuming that’s what she has) affects the skin, not the stomach. But it’s also certainly possible she’s got something else in addition to the a.u., or that she’s sick of burning her lips and cheeks from drips of water, and the shape of a Coke bottle or can prevents dribbles, or something else complicated and strange. Never underestimate people’s ability to be complicated and strange, especially when it comes to medical issues!
Have you ever gotten dry, irritated skin from a pool or hot tub? Your cheeks ever burn after a really long cry? That’s what this is, only it happens with a much wider range of water temperatures and chlorine content, and the reaction may be more dramatic and more painful. Most doctors think it is indeed the chlorine or other chemicals in the water like salt causing the skin to burn and itch, even though it may be very dilute.
Testing consists of dabbing tap water on one inner arm with a cottonball, and distilled water on the other. If you react to the tap water, you have aquagenic urticaria. I’ve yet to read a case study of anyone reacting to distilled water.
Treatment is to avoid skin contact with water as much as possible. That means sponge baths most days, short showers with the water controlled to the temperature that hurts you the least, and no swimming. Some docs prescribe creams, commonly capsaisin, that act as a counter irritant to the nerves, and make the itching or burning feel better. Ultraviolet B therapy may help, and there are some other drug classes (including antihistamines and beta blockers) that some doctors prescribe.
*I know the article implicates histamine, but I went back to my texts and no, there’s no histamine release prior to the symptoms of a.u., unless there’s some very new research I’m unaware of. When the patient scratches, she can cause an inflammatory response and of course histamine is part of that, but it’s the scratching causing the histamine release, not the water.