allergies
"I have a rare skin rash that appears only during summer months. It is an immune system response to heat. Xyzal 10 mg reduces the rash by about 20%, but after about a month, an immunosupressive reaction occurred.  I started getting large, painful pimples in weird places like forearm, hand, and neck. Had a similar reaction to Flonase a few years ago. Immune system can't fight the pimples, so they take over. Disappointing because this is the first oral drug to have an effect on the rash. Hay fever gone too."