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Allergies & the Immune System

Hives (Urticaria)

Lea este articulo en EspanolSeeing red raised spots on your child’s skin can be scary, especially if you don’t know what caused them. Often, though, these spots are a case of the hives — a common skin reaction to something like an allergen (a substance that causes allergies). Most will clear up and go away

If your child has hives, keep him or her as comfortable as possible, then try to figure out what caused them to help prevent them from coming back.

About Hives

Hives (or urticaria) are red raised bumps or welts on the skin. They can appear anywhere on the body and can look like tiny little spots or large interconnected bumps.

Individual hives can last anywhere from a few hours to a week (sometimes longer), and new ones might replace those that fade. Hives that stay for 6 weeks or less are called acute hives; those that go on longer than 6 weeks are chronic hives.

An allergic reaction can cause hives, as can temperature extremes, stress, infections, or illnesses. In some cases, hives are accompanied by angioedema, a condition that can cause swelling around the eyes, lips, hands, feet, or throat. Very rarely, hives and angioedema are associated with an allergic reaction that involves the whole body or anaphylactic shock.


The red welts of hives happen when mast cells in the bloodstream release the chemical histamine, which causes tiny blood vessels under the skin to leak. The fluid pools within the skin to form spots and large welts. This can happen for a number of reasons, but in many cases a cause is never identified.

Most often, hives are associated with an allergic reaction, which can cause the skin to break out within minutes. Common allergies include:

  • foods, especially shellfish, tree nuts, milk, and fruit
  • medications and allergy shots
  • pets and other animals
  • pollen
  • insect bites and stings

Sometimes a breakout of hives has nothing to do with allergies. Other causes include:

  • infections, including colds
  • exercise
  • anxiety or stress
  • exposure to the sun
  • exposure to cold, such as from diving into a cold pool
  • contact with chemicals
  • scratching
  • putting pressure on the skin, such as from sitting too long or carrying a heavy backpack over a shoulder

Hives due to physical causes, such as pressure, cold, or sun exposure, are called physical hives.

It can be hard to figure out what causes chronic urticaria, though it’s sometimes linked to an immune system illness, like lupus. Other times, medications, food, insects, or an infection can trigger an outbreak. Often, though, doctors don’t know what causes chronic hives.

Signs & Symptoms

The hallmark red raised welts of hives sometimes have a pale center, can appear in clusters, and can change shape and location in a matter of hours. They can be from a few millimeters wide to as big as a dinner plate, and can itch, sting, or cause a burning sensation.

If a person also has angioedema, there might be puffiness, swelling, or large bumps around the eyes, lips, hands, feet, genitals, or throat. In severe cases, swelling in the throat can cause breathing trouble and lead to a loss of consciousness.

Rarely, a person with hives and angioedema can also get anaphylactic shock. Signs of anaphylactic shock include difficulty breathing, a drop in blood pressure, dizziness, or a loss of consciousness.


Most of the time, a doctor can diagnose hives just by looking at the skin. To find the cause, you may be asked questions about your child’s medical history, recent exposure to allergic triggers, and daily stressors.

If your child has chronic hives, the doctor may ask you to keep a daily record of activities, such as what your child eats, drinks, and where the hives tend to show up on the body. Diagnostic tests — such as blood tests, allergy tests, and tests to rule out underlying conditions such as thyroid disease or hepatitis — might be done to find the exact cause of the hives.

To check for physical hives, a doctor may put ice on your child’s skin to see how it reacts to cold or place a sandbag or other heavy object on the thighs to see if the pressure will cause hives to appear.


In many cases, mild hives won’t need treatment and will go away on their own. If a definite trigger is found, avoiding it is part of the treatment. If the hives feel itchy, the doctor may recommend an antihistamine medicine to block the release of histamine in the bloodstream and prevent breakouts.

For chronic hives, the doctor may suggest a non-sedating (non-drowsy) prescription or over-the-counter antihistamine to be taken every day. Not everyone responds to the same medications, though, so it’s important to work with a doctor to find the right one for your child.

If a non-drowsy antihistamine doesn’t work, the doctor may suggest a stronger antihistamine or another medicine or a combination of medicines. In rare cases, a doctor may prescribe a steroid pill or liquid to treat chronic hives. Usually this is done for just a short period (5 days to 2 weeks) to prevent harmful steroid side effects.

In Case of Emergency

Anaphylactic shock and bad attacks of hives or angioedema are rare. But when they happen, they need immediate medical care.

Kids with bad allergies should carry an injectable shot of epinephrine to prevent life-threatening allergy attacks. If your child is at risk, the doctor will teach you and your child how to safely give an injection in the event of a severe allergic reaction.

Reviewed by: Rupal Christine Gupta, MD
Date reviewed: August 2014