Allergic Urticaria
"My Dr prescribed Hydroxyzine for my allergic reaction to dust mites and hives and began taking them at night. Best sleep I had in years but it actually increased my hives. It took me a month to figure out it was 
 the Hydroxyzine that was causing my hives.
Two days after I stopped taking it my hives subsided. After 4 days they are almost all gone. It may work for many people but not everyone."