Hives occur when fluid leaks through the cells surrounding tiny blood vessels and enters the skin. This happens when a substance called histamine is released from a specialized type of cells, called mast cells, which lie along the blood vessels in the skin. Allergic reactions to foods or medications can cause the release of histamine by mast cells. In cases of acute urticaria, your child's dermatologist will try to identify the cause of the hives and eliminate it. If necessary, he or she may prescribe a mild antihistamine.
Antihistamines stop the release of histamine from mast cells.
This medication is taken just once a day. Because the hives of chronic urticaria disappear after 12 to 24 hours, and may reappear somewhere else, it is important that the antihistamine be taken regularly, as prescribed by the dermatologist, even if your child's hives have not reappeared. However, drowsiness may occur at more than the recommended dose. The most common side effects occurred about as often as they did with a sugar pill, including headache, drowsiness, fatigue, and dry mouth. At the recommended dose, it won't make kids drowsy or cause hyperactivity.