Merck Manual

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Quick Facts



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Last full review/revision Sep 2019| Content last modified Sep 2019
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What are hives?

Hives are red, itchy, raised patches on your skin.

  • Hives usually come and go away completely, but sometimes they last a long time

  • Allergic reactions often cause hives, but there are other causes

What causes hives?

Hives are usually caused by an allergic reaction to a:

  • Food

  • Insect sting or bite

  • Chemical

  • Medicine

Hives can also be caused by:

  • Stress and other emotional problems

  • Physical factors, such as pressure, cold, heat, and light

  • Autoimmune diseases (diseases that make your immune system attack your own tissues)

Sometimes you and your doctor won't be able to figure out what caused your hives.

When should I see a doctor about my hives?

Call an ambulance if you have hives and:

  • Trouble breathing or wheezing (a whistling sound when you breathe)

  • Your throat feels like it’s closing up

Go to the emergency room or a doctor's office as soon as possible if you have hives and:

  • The hives are severe and getting worse

  • You start feeling weak or light-headed

  • You have a high fever or chills

  • You're throwing up, have pain in your belly, or have diarrhea (frequent, loose, or watery poop)

  • Your hives are dark-colored or turn into open sores

See a doctor if you have:

  • Hives from a bee sting (to talk with your doctor about what to do if you're stung again)

  • Hives that last more than a few days

  • Hives along with fever, weight loss, swollen lymph nodes, joint pain, or night sweats

What are the symptoms of hives?

Hives are usually:

  • Patches on your skin that are red, slightly raised, and have an obvious border, and may be clear in the center

  • On one part of your body or all over

  • Very itchy

How can doctors tell if I have hives?

Your doctor can tell if you have hives by looking at your rash. However, your doctor sometimes will need to do tests to find out why you have hives, especially if you keep having them over and over again.

How do doctors treat hives?

Doctors may not need to treat hives if they go away on their own after a day or two and don't come back. If it's clear what caused the hives, your doctor will have you avoid that substance. To lessen your symptoms, your doctor may:

  • Ask you to bathe in cool water, not scratch your skin, and wear loose clothes until the hives go away

  • Give you certain medicines, such as antihistamine or corticosteroid pills to treat the itching, depending on how severe your symptoms are

  • Ask you to stop taking your medicines, if possible, to see if that helps

Antihistamine pills can make you sleepy, particularly if you're older. Be careful about using them if you have to drive or use power tools. On the other hand, antihistamines may help you sleep at night.

How can I prevent hives?

If you and your doctor find out what caused your hives, you can prevent hives by avoiding that cause. But when hives keep coming back and the cause is unknown, you may need to take certain medicines every day to stop this from happening.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
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