Urticaria is an allergic reaction that can be acute or chronic (when it lasts for more than six weeks). It appears on the skin as red, raised areas that scratch and change places. If there is swelling of the mouth, eyes and difficulty breathing, the person should immediately seek the emergency room. It is usually caused by medications, the most common being analgesics, anti-inflammatories and antibiotics (such as penicillin, sulfa), as well as laxatives. A single tablet can cause hives for a long time. Foods like: seafood, chocolate, peanuts, dried fruits, strawberries, artificial colorants (yellow, orange and red), preservatives and household sprays can also cause hives. However, there are many cases in which the cause is not identified. It should be treated with oral and anti-allergic corticosteroids, indicated by the dermatologist.