Hives (urticaria) are red, raised itchy bumps that can develop over any area of the body. Sometimes they might be related to an allergic reaction to a food, medication, or other allergens. Most of the time, no clear trigger is found. This is called idiopathic urticaria and most patients seen in allergy clinics fall under this category. Extensive allergy testing and laboratory studies is often unnecessary in patients with idiopathic urticaria, and the hives often disappear as suddenly as they first started. Interestingly, stress can play a role in hives.