allergic rhinitis
"Zyrtec worked well for my nasal allergies, but when I tried to stop taking it after several years, I got the skin itch/rash that many have reported.  It was worst for the first few days, but now even a year later I still frequently get a skin rash when I get warm (cholinergic urticaria).  I can't say for sure that the cholinergic urticaria was a side effect of stopping Zyrtec, but skin rashes were never a symptom of mine until I stopped."