Chronic hives often have multiple triggers or often no specific triggers. Examples of possible triggers include stress, cold or hot temperatures, viruses, food, pet dander, medications, exercise, sun exposure, pollen, insect bites, tight clothing, and pressure on the skin. An allergist may help you gain insight into your potential urticaria triggers. Consider documenting your daily foods, medications, stressors, exercise, and exposure to hot or cold temperatures. Something completely unexpected could be triggering your urticaria.