If your baby has 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, it's probably hives. About 15 percent of children get them, and in babies and toddlers, the most common cause is an allergy to a food or medicine. (In older children and adults they can result from a host of triggers, including cold, heat, viral infections, and even stress.)
Hives also usually itch. Cold compresses and an antihistamine such as Benadryl can help relieve itching and may speed the rash's disappearance. If you think your child is having a reaction to pet dander or pollen, bathe him thoroughly to get the irritant off his skin and out of his hair.
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 may have 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 alone are usually not dangerous and should go away on their own. But if your baby's hives are accompanied by swollen lips or eyes or difficulty breathing, 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.
Copyright 2003 Meredith Corporation. Updated 2009.