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Hives, Wheals

What is Urticaria?

Urticaria, commonly known as hives, is a condition in which itchy, red lumps develop on the skin. The lumps, also known as wheals, can form anywhere on the body, but most commonly appear on the limbs and trunk. They frequently appear as large irregular patches, and although they usually only last several hours, they can occasionally last for several days.

Although the cause of urticaria is often unknown, the most common known cause is an allergic reaction. When an allergic reaction is triggered, skin cells release a chemical called histamines. Histamines cause fluid to leak from minute blood vessels (capillaries) into the surrounding skin, causing the wheals to form. Factors that can trigger this type of allergic reaction include eating particular foods (such as wheat, milk, chocolate, eggs, shellfish, strawberries, or nuts), food additives (including some food dyes), medications (antibiotics, analgesics), contact with certain plants (nettles) or fabrics, insect stings, and occupational contact with sensitizing chemicals or animal proteins. Occasionally urticaria occurs in reaction to sweating due to heat or exercise, exposure to cold or exposure to sunlight. The condition appears to be made worse by stress. Frequent, recurring episodes of urticaria over a period greater than six weeks are known as chronic urticaria. In 75% of these cases, no cause is ever found.

How is it diagnosed?

History: Red (or pale) extremely itchy wheals have erupted on the skin. They are usually on the limbs or trunk but can be anywhere on the body. The individual may have a known history of allergies. A diet history may detect consumption of a known offender. Individual may be taking a new medication for a current illness, or an unfamiliar form of a medication known to cause them an allergic reaction.

Physical exam should distinguish urticaria wheals from other skin rashes.

Tests will include an allergy screen to identify allergic factors that need to be avoided in the future.

How is urticaria treated?

Because urticaria is an allergic reaction, the cause needs to be identified, removed, and avoided if possible. Diet might need to be modified. Medications (plus their derivatives) need to be identified, avoided and alternatives substituted. Since there is no known cause in 75% of chronic urticaria cases, symptomatic treatment (relieving symptoms) is the choice. This includes a soothing bath or the application of calamine lotion. Some calamine lotions also contain a topical antihistamine. Oral antihistamine medications often give quick relief. An injection under the skin (subcutaneous) of a vasoconstrictor and bronchodilator or an anti-inflammatory medication (corticosteroid) may be necessary for more severe or incapacitating cases.


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Decrease activities until several days after hives disappear. Avoid getting hot, sweaty or excited.


  • If foods are suspected as a cause, keep a food diary to help identify the offending food.
  • Avoid alcohol and coffee or other caffeine-containing beverages if they appear to trigger outbreaks.

What might complicate it?

Complications may include not being able to identify and/or eliminate the causative agent, ineffective symptom relief from treatment, and the severity of the reaction. If the hives are associated with angioedema, an anaphylactic reaction is possible. Anaphylaxis is a medical emergency.

Predicted outcome

The wheals can last for several hours. Identifying and avoiding known trigger factors can help prevent allergic reactions in the future. Even if the trigger source cannot be identified, the allergic reactions can lessen in frequency and severity over time without treatment.


Differential diagnoses include erythema multiforme and erythema nodosum.

Appropriate specialists

Allergist, dermatologist, and immunologist.

Seek Medical Attention

The following occur during an episode of hives:

  • Swollen lips.
  • Shortness of breath or wheezing.
  • A tight or constricted feeling in the throat.
  • Any of the symptoms of anaphylaxis. This is an emergency!

Last updated 4 April 2018