I know someone who has the same problem, and i do believe it is from the chlorine of the pool, it does not happen when he takes a shower, swims in the ocean, or any other water activity unless the water is chlorinated. If you check on line there are many others with the same problem maybe they are just not going to the doctor over it, the person i know has stopped swimming altogether because of it, they would rather not swim then deal with the pain of the rash. I've been looking around for solutions for them you might want to check out Dermaswim Pro, I'm going to let my friend know about it as well. Good Luck
Rick:
Despite its reputation, chlorine rarely causes problems. Some people develop hives from water. Do you get welst when you take a shower? Swim in the ocean? If there is any way, try to induce the welts and then have a dermatologist see you when they're there (or failing that, take a good picture of them.) I have yet to see a patient who had to stop pool swimming altogether because of sensitivity.
Best.
Dr. Rockoff