How can you tell whether you have hives or allergic reactions?

Hives is swelling: Hives is swelling with no rash. Hives are caused by a reaction to food, drug, or infection.There are also physical hives to cold , heat, or exercise.

Histamine driven: Hives (or welts) are histamine driven reactions. These lesions come and go within hours and do not leave scales or marks. Hives can be a form of allergic reaction (ie to drugs or shellfish), but they can often be idiopathic (unknown trigger). Because we know this is a histamine driven problem, we treat with oral antihistamines, or oral steroids if severe and associate with wheezing.