What are hives?

Hives are red, itchy, swollen areas of the skin. They can vary in size from as small as a pencil eraser to as large as a dinner plate. Hives, which are also known as urticaria, appear suddenly and may leave in one to two hours. They often appear in clusters, with new clusters appearing as other areas of the skin clear. Hives can appear on any part of the body.

Hives do not leave a permanent mark on the skin and more than 20 percent of the population has suffered an eruption of hives at some point in their lives.

There are several different types of hives, including:

• Dermatographism, which occurs in 5% of the population. These hives are caused by stroking or rubbing the skin, and often occur after scratching, or when tight-fitting clothes rub the skin.
• Cholinergic urticaria are hives that develop when the body temperature rises. This can be due to warm baths or showers, jacuzzi or hot tub use, exercise, a fever or emotional stress. An estimated 5 to 7% of patients who have hives experience cholinergic urticaria.
• Cold-induced hives occur after exposure to cold wind or water. Hives may appear on arms or legs and may affect any exposed area. Cold water/liquids or frozen foods such as ice cream can provoke symptoms on the lips or in the mouth.
• Solar hives are caused by exposure to sunlight or to a sunlamp. A reaction can occur within one to three minutes.

Hives that last for less than six weeks are called acute hives. Those that last longer than six weeks are called chronic hives. In general, chronic hives are often idiopathic, meaning that the trigger is not clear or unknown.

Visit the Vaccine Education Center for pictures and additional information about hives and other rash-related illnesses.

Signs and symptoms of hives

Hives are raised, red welts. They can:

• Be pale at the center
• Appear in clusters
• Change shape and appear on different parts of the body
• Itch, sting or burn

Causes of hives

Hives appear when blood plasma leaks out of small blood vessels in the skin. This leakage occurs when the body releases histamine, a chemical that defends against harmful substances.

Triggers may include:

Infections and illness

Illnesses and infections are among the most common cause of hives in children. Common infections that may cause hives include colds and some bacterial or fungal infections. Illnesses such as vasculitis, lupus and thyroid disease, can also cause hives.

Foods

Illnesses and infections are among the most common cause of hives in children. Common infections that may cause hives include colds and some bacterial or fungal infections. Illnesses such as vasculitis, lupus and thyroid disease, can also cause hives.

Medications/Drugs

Almost any prescription or over-the-counter medication can cause hives. Medications often responsible for producing hives are: penicillin, sulfa drugs, aspirin and ibuprofen. In addition, antacids, vitamins, eye and ear drops, laxatives or any other non-prescription item can cause hives.

Environment

Dust, animals, pollen and molds can also cause hives. Coming into contact with detergents, fabric softeners, hair sprays and latex can cause hives in people who are allergic or sensitive to those substances.

Insects

Insect bites and stings can cause hives.

Exercise

Some affected individuals can develop a lung obstruction and/or lose consciousness from hives that occur during exercise. Such a severe reaction is called exercise-induced anaphylaxis. If this occurs, call 911 immediately.

Testing and diagnosis of hives

Your child’s doctor will look at your child’s skin to diagnose hives. It can be challenging to find the cause, so your doctor will ask about recent illnesses, medication, foods your child has eaten and other possible causes. Your child’s doctor may also order one or more of the following tests:

Skin test

In allergy skin testing, a very small amount of certain allergens are introduced to the skin — typically on your child’s forearm — through a gentle pinprick. The appearance of a hive-like bump may indicate an allergy to that substance.

Blood test

A small amount of your child's blood is drawn and tested for illness or infection that might have caused the hives. Blood tests can also identify if your child's body is producing antibodies to a potential allergy from food or environmental causes.

Skin biopsy

In rare circumstances, a dermatologist may examine a small amount of affected skin under a microscope.

Treatments for hives

Hives often clear up on their own. If it is caused by a food or other known trigger, you can take steps to avoid future outbreaks if you know what triggered your child’s hives. Otherwise, antihistamines can be effective in treating hives.

If your child's hives do not respond to antihistamines, your provider can work with you to come up with a regimen to help control the symptoms.

Follow-up care for hives

If your child’s hives are an allergic reaction to certain foods or other substances, you may want to let extended family, close friends and your child’s school know so they can help keep your child from being exposed, and what to do if there is an accidental exposure. If your child has diagnosed food allergies, they should carry epinephrine with them, or it should be readily available at places where they routinely spend time, such as school, daycare and home.

If your child gets frequent hives, you and your family can receive ongoing treatment, education and support through the Allergy Program at Children’s Hospital of Philadelphia (CHOP).

Long-term outlook for hives

Hives usually clear up on their own, though some cases of chronic hives can last months to a year or longer.

Reviewed by: Allergy Section
Date: January 2020