IgE-mediated urticaria and angioedema, serum sickness and idiosyncratic mechanisms all cause rashes. However, only mechanisms involving IgE should be labelled allergic, and they are the only ones with potentially fatal results. The most common type of rash seen by an allergy specialist is urticaria, acute and chronic. Acute urticaria lasts less than six to eight weeks and is most often caused by infection, medication and some foods. Chronic urticaria is caused by animal dander, ASA, certain food additives and some systemic diseases. Treatment is removal of the allergen, plus H1 and H2 antagonists and beta agonists. Both forms of urticaria eventually resolve spontaneously.