Urticaria (hives) is an allergic reaction that can be acute or chronic (when it lasts more than six weeks). It appears in the skin as red, elevated plaques, that are very itchy and migrate from one site to another. If there is mouth or eye swelling or difficult breathing, the person should immediately seek for the emergency department. Usually it is caused by drugs, being the most frequent analgesics, anti-inflammatories and antibiotics (such as penicillin, sulphonamides), besides laxatives. Only one pill can cause urticaria for a long time. Foods like: seafood, chocolate, peanuts, dry fruits strawberry, artificial food coloring (yellow, orange and red), conservatives and domestic use sprays also can cause urticaria. However, there are many cases in which the cause is unidentified. It should be treat with oral corticoids and anti-allergics, prescribed by the dermatologist.