Hives are raised, often itchy, red bumps (welts) on the surface of the skin. They are usually an allergic reaction to food or medicine.
Causes, incidence, and risk factors
When you have an allergic reaction to a substance, your body releases histamine and other chemicals into the blood. This causes itching, swelling, and other symptoms. Hives are a common reaction. Persons with other allergies, such as hay fever, often get hives.
When swelling or welts occur around the face, especially the lips and eyes, it is called angioedema . Swelling can also occur around your hands, feet, and throat.
Many substances can trigger hives, including:
- Animal dander (especially cats)
- Insect bites
- Shellfish, fish, nuts, eggs, milk, and other foods
Hives may also develop as a result of:
- Swelling of the surface of the skin into red- or skin-colored welts (called wheals) with clearly defined edges.
- Wheals may get bigger, spread, and join together to form larger areas of flat, raised skin.
- Wheals can also change shape, disappear, and reappear within minutes or hours.You know you have hives when you press the center of a wheal, it turns white. This is called blanching.
Signs and tests
Your doctor can tell if you have hives by looking at your skin.
If you have a history of an allergy, then the diagnosis is even more obvious.
Sometimes, a skin biopsy or blood tests are done to confirm that you had an allergic reaction, and to test for the substance that caused the allergic response.
Treatment may not be needed if the hives are mild. They may disappear on their own. To reduce itching and swelling:
- Do not take hot baths or showers.
- Do not wear tight-fitting clothing, which can irritate the area.
- Your health care provider may suggest that you take an antihistamine such as diphenhydramine (Benadryl). Follow your provider's instructions or package instructions about how to take the medicine.
If your reaction is severe, especially if the swelling involves your throat, you may require an emergency shot of epinephrine (adrenaline) or a steroid. Hives in the throat can block your airway, making it difficult to breathe.
Hives may be uncomfortable, but they are usually harmless and disappear on their own. In most cases, the exact cause of hives cannot be identified.
- (a life-threatening, whole-body allergic reaction that causes breathing difficulty)Anaphylaxis
- Swelling in the throat can lead to life-threatening airway blockage
Calling your health care provider
Call 911 or your local emergency number if you have:
- Shortness of breath
- Tightness in your throat
- Tongue or face swelling
Call your health care provider if the hives are severe, uncomfortable, and do not respond to self-care measures.
- Avoid exposure to substances that give you allergic reactions.
- Do not wear tight-fitting clothing and do not take hot baths or showers just after having hives. These can cause hives to return.
Habif TP. . 5th ed. Philadelphia, Pa.: Elsevier Mosby; 2009:chap 9.