Acute urticaria is a sudden outbreak of raised, itchy welts that typically resolves within days to a few weeks. It is often triggered by an infection, a food, an insect sting, or a medicine, although in many cases no trigger is ever identified.
Hives accompanied by swelling of the lips, tongue, or throat, difficulty breathing, or faintness may signal a severe allergic reaction and are treated as an emergency rather than an itching problem.