This information was reviewed and approved by
Christine B. Cho, MD (4/1/2019).
What causes hives (urticaria)?
No identifiable cause: In many cases, no cause is identified, and the hives are thought to occur spontaneously. This form of hives is often called Recurrent Spontaneous Urticaria or Chronic Idiopathic Urticaria. It has a good prognosis. Most cases resolve over time. The hives can recur more frequently or more severely with concurrent infection, stress, heat and NSAID or alcohol use.
Allergies: When hives are caused by allergies, they happen immediately (within minutes) of being exposed to the allergen.