I have lived with excercise induced hives for the last 4 years. I tried using claritin and any type of antihistamine I could get a hold of. I would take it about a half hour before I would exercise and it never seemed to work. I finally went to the doctor after having a very severe reaction to running outside like I had been doing for years. I had hives on my palms, bottom of my feet, in my ears, and down my throat. The doctor prescribed atarax (hydroxine) along with claritin. I take these at night. I have been able to resume working out and running outside. Hope this helps.