What are hives?
Hives are an itchy skin rash -- red, raised bumps with a paler center - triggered by an irritant. They can show up anywhere on your child's body, from the skin to the inside of his mouth, and vary in size from 1/16 inch in diameter to many inches across. Hives, also known as urticaria or wheals, can pop up in one area, fade, and appear in a totally different place within a matter of hours. Studies show that 2 to 20 percent of children develop hives at one time or another. An episode of hives can be over in a few hours, but most take about 48 hours to completely disappear. Some stubborn cases may even last a few weeks.
What causes them?
Common triggers include food allergies, drugs, viruses, insect bites and stings, plants, exercise, heat, and cold. Unfortunately, finding the cause of your child's hives is rarely easy; many times, you and your doctor will be unable to identify the exact cause. And like most allergic reactions, your child may have been exposed to the irritant in the past without any problem. Here are some common triggers:
- Food allergies. The most common culprits include nuts, eggs, shellfish, strawberries, and tomatoes. Food additives, including monosodium glutamate, also cause hives in some children.
- Viral infections. The offending viral infections include infectious mononucleosis (Epstein-Barr virus); hepatitis A, B, or C; adenovirus; and enterovirus. (Many of these illnesses have other symptoms in addition to hives.)
- Prescription and over-the-counter drugs. These include codeine, nonsteroidal anti-inflammatory drugs like ibuprofen, and antibiotics like penicillin and cephalosporin. Aspirin may also cause hives -- and it's associated with Reye's syndrome, a rare but potentially life-threatening disorder; it should not be given to anyone under 20.
Among kids taking those medications, hives may appear immediately after the first dose or sometimes days into the treatment. What's more, hives don't always appear the first time your child takes a particular medication; sometimes they erupt after he has taken the medicine on several different occasions.
- Insect bites. Children tend to react much more strongly than adults to bites from mosquitoes, fleas, and red mites (commonly known as chiggers). The bites tend to be on body parts not covered by clothing, and each crop of hives can last 10 to 14 days. Stings from bees, wasps, scorpions, spiders, and jellyfish can also cause hives.
- Changes in the environment. It's rare, but occasionally cold, heat, and sun exposure can trigger hives in susceptible individuals. Sometimes hives can be a sign of an underlying disease, like lupus, juvenile rheumatoid arthritis, or inflammatory bowel syndrome.
What makes the hives appear?
Some children are simply more susceptible to certain irritants than others. Their immune systems reacts more quickly -- sometimes even to substances that are usually harmless -- and attack what appears to be an invader. When this occurs, the immune system releases a chemical called histamine to combat the irritants. Histamine makes blood vessels in the skin leaky, and the fluid that escapes gets trapped in the lower level of the skin, causing the bumpy hives. Histamine also provokes the itchy feeling that accompanies hives.
Hives triggered by heat, cold, sun, and exercise are more of a mystery. Scientists don't yet know exactly why these rashes appear.
When should I call the pediatrician?
Most hives are harmless, but they can also signal a serious or even life-threatening condition. Contact your pediatrician or call 911 immediately if your child has any of these symptoms:
- Hives in or swelling around the mouth
- Wheezing or difficulty breathing
- Pale, clammy skin
- Hives or difficulty breathing after an insect sting
In those instances, hives can be a sign of anaphylactic shock, a potentially fatal allergic reaction. These episodes progress rapidly, and can cause enough swelling around the lips, tongue, and mouth to block the airway; your child's blood pressure can also drop rapidly. If your child has a history of severe allergy to insect stings or foods and is carrying epinephrine, give him an injection and then seek medical attention immediately.
You should also contact a pediatrician for a non-emergency appointment in these circumstances:
- Your child has been taking medication and develops hives or a rash.
- He has had hives in the past and they recur.
- An episode of hives lasts more than four hours.
- The hives are accompanied by a fever of more than 100 degrees Farenheit, abdominal pain, or painful, swollen joints. Those symptoms can be signs of infection or disease.
How do I treat hives?
You can use cool compresses or a cool bath to reduce irritation and itching, but since hives are a reaction to histamine, antihistamines are usually the most effective treatment. Benadryl (its generic name is diphenhydramine) is available over-the-counter in liquid and pills. Follow the dosing guidelines carefully (and contact your doctor for children under 2-years-old). Give Benadryl every 6 hours until the hives fade. Continue the medication, spacing the doses farther and farther apart, until you are sure the hives are no longer a problem.
Your pediatrician may also recommend hydroxazine (Atarax), a prescription antihistamine. (Let your doctor know if you're using any over-the-counter medications for the hives.) Be aware that antihistamines make most children a little drowsy.
How can I protect my child from hives?
Avoid the irritant, if you know what it is. Teach your child to avoid trigger foods, and alert family, friends, school, and daycare. If your child is severely allergic, ask your pediatrician for a Medi-Alert bracelet, which will let medical workers know how to proceed in an emergency.
Children with a history of life-threatening hives from foods or insect stings should carry epinephrine with them at all times. Epinephrine is available in automatic injection devices; talk to your pediatrician about when to use it, and always seek medical attention immediately after giving it.
Pantell, Robert H. M.D., James F. Fries M.D., and Donald M. Vickery M.D. Taking Care of Your Child: A Parent's Illustrated Guide to Complete Medical Care, Eighth Edition. 2009. Da Capo Lifelong Books.
Sidney Hurwitz, Clinical Pediatric Dermatology: A Textbook of Skin Disorders of Childhood and Adolescence, 2nd ed. W B Saunders Co 1993.
Weston WL, Badgett JT. Urticaria. Pediatrics in Review Jul 1998;19(7):240-43.