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Also known as Urticaria or Wheals
We have selected the following expert medical opinion based on its clarity, reliability and accuracy. Credit: Sourced from the MSD Manual, Consumer Version; authored by Dr Mercedes E. Gonzalez MD (see below). Please refer to your own medical practitioner for a final perspective, assessment or evaluation.
Hives are red, itchy, slightly elevated swellings. Itching may be severe. Hives have clearly defined borders and may have a pale centre. Typically, crops of hives come and go. One hive may remain for several hours, then disappear, and later, another may appear elsewhere. After the hive disappears, the skin usually looks completely normal. The swelling is caused by the release of chemicals (such as histamine) from mast cells in the skin, which cause fluid to leak out of small blood vessels temporarily.
Hives (Urticaria, Wheals)
Photo provided by Dr Thomas Habif, MD.
Hives may occur with angioedema, which, like hives, involves swelling. However, the swelling of angioedema is under the skin rather than on its surface. Sometimes angioedema affects the face, lips, throat, tongue, and airways. It can be life threatening if the swelling interferes with breathing.
Hives and angioedema are often allergic reactions.
Hives may occur when certain chemicals are inhaled, consumed, injected, or touched. These chemicals can be in the environment, foods, drugs, insects, plants, or other sources. They are harmless in most people. But if people are sensitive to them, these chemicals (called triggers or allergens) can cause an allergic reaction. That is, the immune system overreacts to the chemicals.
However, hives are not always part of an allergic reaction. For example, they may result from autoimmune disorders. In these disorders, the immune system malfunctions, misinterpreting the body's own tissues as foreign and attacking them. Also, some drugs cause hives directly without triggering an allergic reaction. Emotional stress and some physical conditions (such as heat or light) may cause hives for reasons that are not well understood.
Hives usually last less than 6 weeks and are classified as acute. If hives last more than 6 weeks, they are classified as chronic.
Acute hives are most commonly caused by:
Chronic hives are most commonly caused by:
Not every episode of hives requires immediate evaluation by a doctor. The following information can help people decide whether a doctor's evaluation is needed and help them know what to expect during the evaluation.
People should call an ambulance if:
People should see a doctor if:
Doctors first ask questions about the symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause and the tests that may need to be done.
Doctors ask the person to describe each episode of hives in detail and any other symptoms that occurred (such as itching, difficulty breathing, or swelling of the face and tongue). They ask about the person’s activities before and during the episode and about possible exposure to substances that can trigger allergic reactions, including drugs being taken. The person is also asked about specific symptoms that could suggest a cause (see Table: Some Causes and Features of Hives), past allergic reactions, and recent travel.
The trigger is not always clear from the history, often because the trigger is something that may have been tolerated previously.
During the physical examination, doctors first check to see whether the lips, tongue, throat, or airways are swollen. If there is swelling, they begin treatment right away. Then doctors note how the hives look, determine which parts of the body are affected, and check for other symptoms that may help confirm the diagnosis. Doctors may use various physical stimuli to see whether they can trigger the hives. For example, they may apply light pressure, heat, or cold to the skin or stroke the skin.
People themselves should not try to trigger their hives, because a severe reaction could occur.
Drugs such as:
Hives that start within 48 hours after the drug was used.
For most stimuli, hives that typically start within seconds or minutes of exposure to the stimulus.
For pressure on the skin, hives that start within 4–6 hours and affect only the area of the skin pressed.
For sunlight, hives that affect only the area of the skin exposed to sunlight.
Foods that trigger an allergic reaction (food allergens), such as peanuts, nuts, fish, shellfish, wheat, eggs, milk, and soybeans
Infections (rare causes):
Insect bites or stings:
Substances that trigger an allergic reaction through contact (contact allergens), such as latex, animal saliva or dander, dust, pollen, or moulds
Systemic lupus erythematosus (lupus)/ Sjogren’s syndrome/ Urticarial vasculitis
Cancer, typically of the digestive organs or lungs, or lymphoma (rare cause):
Chronic idiopathic hives (diagnosed when no specific cause is identified):
Drugs (same as those for acute hives):
Emotional or physical stimuli (same as those for acute hives):
Endocrine abnormalities such as a thyroid disorder or an elevated level of progesterone (a female hormone):
Usually, testing is not needed for a single episode of hives unless symptoms suggest a specific disorder that requires treatment (such as some infections). But if hives have unusual characteristics, recur, or persist, tests are usually done.
Typically, tests include a complete blood cell count and blood tests to measure levels of electrolytes, sugar (glucose), and thyroid-stimulating hormone and to determine how well the kidneys and liver are functioning.
Skin tests, such as a skin prick test, are done by an allergist (a doctor who specializes in allergic disorders) to identify specific allergens. Imaging and other blood tests are done based on results of the history and physical examination. If results suggest that the cause is a bodywide disorder, a thorough evaluation is needed to identify the cause.
A skin biopsy may be done if the diagnosis is unclear.
Hives often go away on their own after a day or two. If the cause is obvious or if the doctor identifies a cause, people should avoid it if possible. If the cause is not obvious, people should stop taking all nonessential drugs until the hives subside.
Bathing and showering with only cool water, refraining from scratching, and wearing loose clothing may help relieve symptoms.
In about half the people with chronic hives, the hives disappear without treatment within 2 years. In some adults, the antidepressant doxepin, which is also a potent antihistamine, helps relieve chronic hives. Omalizumab, a monoclonal antibody, may be used by people whose chronic hives have continued to occur despite other treatments.
Older people are more likely to have side effects when they take the older antihistamines (such as hydroxyzine and diphenhydramine). In addition to drowsiness, these drugs can cause confusion and delirium and can make starting and continuing to urinate difficult. Usually, older people should not take these drugs for hives.
Dr Mercedes E. Gonzalez
Clinical Assistant Professor of Dermatology, University of Miami Miller School of Medicine; Clinical Assistant Professor of Dermatology, Florida International University Herbert Wertheim College of Medicine and Medical Director, Paediatric Dermatology of Miami
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