acute and chronic(when hives persist for
more than 6 weeks). The most likely triggers for
acute urticaria are allergies to pets, horses, latex and foods, such as shellfish and nuts, bee or wasp stings, allergies to medicines, Viral infections, such as glandular fever and herpes, dental and sinus infections, fungal infections, blood transfusions and vaccines.
The cause of chronic urticaria is often more difficult to identify.