Urticaria usually presents as raised, erythematous wheals accompanied by intense pruritus. The lesions typically last a few hours, only to fade and reappear elsewhere. Urticaria may be classified as either acute or chronic. Typically, lesions lasting less than 6 weeks are referred to as acute urticaria. Acute urticaria is more common in young people and is most likely due to exposure to food allergens , food additives, certain medications, or radiocontrast media. Certain antibiotics may produce acute urticaria by either IgE- or IgG-mediated mechanisms(referred to as Arthus phenomenon).