Flat or slightly raised red blotches with wavy borders that appear on any part of the body, and fade from one area while reappearing in others, are probably hives. About 15 percent of children get them. In babies and toddlers, the most common cause is an allergy to a food or medicine. But in older children and adults they can result from a host of factors, including cold, heat, viral infections, and even stress.
The cause of hives is sometimes elusive: You may suspect that a certain food is behind them, but the next time your child eats that same food, he has no reaction. If your child is taking a medication at the time the hives appear, your pediatrician may label your child as allergic to that drug. The trouble with this is that children sometimes react to the flavoring or coloring of the medication rather than to the drug itself. If you find that every antibiotic seems to cause hives, consult an allergist to determine the true sensitivity.
Hives usually itch. Cold compresses and an antihistamine such as Benadryl can help relieve itching and may speed the rash's disappearance.
When to Worry:
If hives are accompanied by swollen lips, difficulty breathing, and swollen eyes, call 911; your child is suffering from a severe allergic reaction. Hives accompanied by swollen lips and sore joints, or bruising or discoloration left after the hives fade, can be signs of an inflammation of small blood vessels that can affect the kidneys or other organs. See your pediatrician.