What can cause huge itchy hives that last for 2 days? Responds to antihistamine but returns hours later. No known allergies but strong family history.

Acute Urticaria/Hive. Acute urticaria (hives) is common, affecting 20% of the population. Acute hives resolve within 6 weeks (most patients fit into this category). Hives can become chronic if last more than 6 weeks. Common viral/bacterial infections can trigger an outbreak, however medications, foods, and stings can also cause acute hives but have the potential to lead to more serious complications. See Allergist.