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Hives !hIvz

by Karen McKoy, MD, MPH

Hives (urticaria) are red, itchy, slightly elevated swellings. Itching may be severe. Hives have clearly defined borders and may have a clear center. 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 may occur with angioedema (see Angioedema), which, like hives, involves swelling. However, the swelling caused by 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.

Causes

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

  • Allergic reactions

  • Nonallergic reactions

Allergic reactions are often triggered by foods, particularly eggs, fish, shellfish, nuts, and fruits, or by insect stings. Eating even a tiny amount of some foods can suddenly cause hives. But with other foods (such as strawberries), an allergic reaction occurs only after a large amount is eaten. Many drugs, particularly antibiotics, may cause hives. Immediate allergic reactions may also occur when a substance comes into direct contact with the skin (such as latex), after an insect bite, or as a reaction to a substance that is inhaled into the lungs or through the nose.

Nonallergic causes of hives include infections, some drugs, some physical stimuli (such as pressure or cold), and some food additives.

Even though acute hives usually have a specific cause, the cause cannot be identified in about half of cases.

Chronic hives are most commonly caused by

  • Unidentified (idiopathic) conditions

  • Autoimmune disorders

Sometimes the cause is easily overlooked, as when people repeatedly consume a food not known to be a trigger, such as a preservative or dye in foods or penicillin in milk. Sometimes, despite the best efforts, the cause remains unidentified.

Chronic hives can last for months or years, then sometimes go away for no apparent reason.

Evaluation

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.

Warning signs

Certain symptoms and characteristics are cause for concern:

  • Swelling of the face, lips, throat, tongue, or airways (angioedema)

  • Difficulty breathing, including wheezing

  • Hives that are deeply colored, that become open sores, or that persist more than 48 hours

  • Fever, swollen lymph nodes, jaundice, weight loss, and other symptoms of a bodywide (systemic) disorder


When to see a doctor

People should call an ambulance if

  • They have difficulty breathing or are wheezing.

  • Their throat feels as if it is closing up.

People should go to an emergency department or a doctor's office as soon as possible if

  • Their symptoms are severe.

  • They feel progressively weak or light-headed or have severe fever or chills.

  • They are vomiting or have abdominal pain or diarrhea.

People should see a doctor if

  • A bee sting triggers hives (to obtain advice about treatment if another bee sting occurs).

  • They have other symptoms, such as fever, joint pains, weight loss, swollen lymph nodes, or night sweats.

  • Hives recur without exposure to a trigger.

  • Symptoms last for more than 2 days.

If children have hives that appear suddenly, disappear quickly, and do not recur, an examination by a doctor is usually unnecessary. The cause is usually a viral infection.


What the doctor does

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 (see Some Causes and Features of Hives).

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 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.

Some Causes and Features of Hives

Cause

Common Features*

Tests

Acute hives (lasting less than 6 weeks)

Drugs such as

  • Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs)

  • Some opioids

  • Vancomycin

  • Succinylcholine (sometimes given before surgery)

  • Contrast agents (used with imaging tests such as computed tomography)

  • Possibly any drug, whether prescription, over-the-counter, or herbal, if people are allergic to it

Hives that start within 48 hours after the drug was used

A doctor's examination

Emotional or physical stimuli

  • Stress or anxiety

  • Cold

  • Exercise

  • Pressure on the skin (dermatographism)

  • Heat

  • Sunlight

  • Sweating as occurs during a warm bath, exercise, or fever

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

A doctor's examination

Exposure to the suspected physical stimulus to see whether it triggers symptoms

Foods that trigger an allergic reaction (food allergens), such as peanuts, nuts, fish, shellfish, wheat, eggs, milk, and soybeans

Hives that start within minutes or hours after consumption

A doctor's examination, particularly the medical history

Sometimes allergy skin prick testing

Infections (rare causes)

  • Bacterial, such as some urinary tract, streptococcal, and Helicobacter pylori infections

  • Parasitic, such as Toxocara canis, Giardia intestinalis (lamblia), Schistosoma mansoni, Strongyloides stercoralis, Trichuris trichiura, and Blastocystis hominis infections

  • Viral, such as hepatitis (A, B, or C) and HIV, cytomegalovirus, Epstein-Barr virus, and enterovirus infections

Fever, chills, and fatigue

Symptoms of the particular infection

Particularly for parasitic infections, recent travel to a developing country

Tests depending on the suspected infection (suggested by results of the medical history and examination)

Diagnosis confirmed if hives disappear after the infection is eliminated

Insect bites or stings

Hives that start within seconds or minutes after an insect bite or sting

A doctor's examination, particularly the medical history

Serum sickness

Hives that start within 7–10 days after injection of

  • A blood product (as in a transfusion)

  • A drug derived from animal blood such as horse serum (which is used to treat poisonous snake and spider bites)

  • Possibly another drug

May be accompanied by fever, joint pain, swollen lymph nodes, and abdominal pain

A doctor’s examination

Substances that trigger an allergic reaction through contact (contact allergens), such as latex, animal saliva or dander, dust, pollen, or molds

Hives that start within minutes or hours after contact

A doctor's examination, particularly the medical history

Sometimes allergy testing

Transfusion reactions

Hives that usually start within a few minutes after transfusion of a blood product

A doctor's examination, particularly the medical history

Chronic hives (lasting more than 6 weeks)

Autoimmune disorders

  • Systemic lupus erythematosus (lupus)

  • Sjögren syndrome

  • Urticarial vasculitis

Various symptoms depending on the autoimmune disorder

For systemic lupus erythematosus, symptoms may include fever, fatigue, headache, joint pain and swelling, painful breathing, and mouth sores

For Sjögren syndrome, dry eyes and dry mouth

For urticarial vasculitis, hives that

  • May be painful rather than itchy

  • Usually last more than 24 hours

  • Do not whiten (blanch) when pressure is applied

  • Can be accompanied by small blisters and reddish purple blotches (purpura)

For all autoimmune disorders, blood tests to check for abnormal antibodies

Sometimes skin biopsy

For Sjögren syndrome, a test that estimates the amount of tears people are producing

For urticarial vasculitis, skin biopsy

Cancer, typically of the digestive organs or lungs, or lymphoma

Weight loss, night sweats, abdominal pain, cough (sometimes bringing up blood), jaundice, swollen lymph nodes, or a combination

Various tests depending on the cancer suspected

Chronic idiopathic hives (diagnosed when no specific cause is identified)

Hives that occur daily (or almost daily) and itching that lasts for at least 6 weeks, with no obvious cause

A doctor’s examination

Blood and sometimes other tests, such as skin prick tests and exposure to various triggers, to rule out other causes

Drugs (same as those for acute hives)

Hives that occur in a person who has been taking a prescription, an over-the-counter, or an herbal drug for a long time when there is no other explanation for them

A doctor's examination

Sometimes allergy testing

Trial of avoidance to see whether hives disappear after the drug is stopped

Emotional or physical stimuli (same as those for acute hives)

For most stimuli, hives that typically occur 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

A doctor's examination

Exposure to the suspected stimulus to see whether it triggers symptoms

Endocrine abnormalities such as a thyroid disorder or an elevated level of progesterone (a female hormone)

For thyroid disorders, difficulty tolerating heat or cold, a slow or fast heart rate, and shaking (tremor) or sluggishness

Occurring in women who take birth control pills (oral contraceptives) or hormone therapy containing progesterone or who have hives appearing just before their menstrual periods start and disappearing when periods stop

A doctor's examination

If a thyroid disorder is suspected, a blood test to measure thyroid-stimulating hormone

Mastocytosis

Small red bumps that turn into hives when touched

Sometimes abdominal pain, easy flushing, and recurring headaches

Skin and sometimes bone marrow biopsy

Sometimes blood tests to measure levels of substances released when certain immune cells (called mast cells) are activated

*Features include symptoms and results of the doctor's examination. Features mentioned are typical but not always present.

HIV = human immunodeficiency virus.


Testing

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 (see Diagnosis). 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 is done if the diagnosis is unclear or if hives last more than 48 hours.


Treatment

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.

Drugs

For hives, antihistamines are used. These drugs partially relieve the itching and reduce the swelling. To be effective, they must be taken regularly, rather than as needed. Several antihistamines, including cetirizine, diphenhydramine, and loratadine, are available without a prescription. Diphenhydramine is an older drug that is more likely to cause drowsiness than the other two. Other antihistamines include desloratidine, fexofenadine, hydroxyzine, and levocetirizine.

If symptoms are severe and other treatments are ineffective, corticosteroids, such as prednisone, taken by mouth, are used. They are given for as short a time as possible. When taken by mouth for more than 3 to 4 weeks, corticosteroids have many, sometimes serious, side effects (see Corticosteroids: Uses and Side Effects). Corticosteroid or antihistamine creams do not help.

People who have severe reactions should carry a self-injecting epinephrine pen and, if a reaction occurs, use it immediately.

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.


Essentials for Older People

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.

Key Points

  • Hives may or may not be an allergic reaction.

  • If hives have lasted less than 6 weeks, the cause is usually an allergic reaction to a specific substance, an acute infection, or a nonallergic reaction to a specific substance.

  • If hives have lasted 6 weeks or more, the cause usually cannot be identified (is idiopathic) or is an autoimmune disorder.

  • People should call an ambulance if they have difficulty breathing or if their throat feels as if it is closing up.

  • People with mild symptoms should avoid any known or suspected triggers and can take antihistamines to relieve symptoms.

  • People who have severe reactions should carry a self-injecting epinephrine pen and, if a reaction occurs, use it immediately.

Resources In This Article

Drugs Mentioned In This Article

  • Generic Name
    Select Brand Names
  • No US brand name
  • VANCOCIN
  • CRINONE
  • ANECTINE, QUELICIN
  • ADRENALIN
  • ALLEGRA
  • XYZAL
  • VISTARIL
  • ZONALON
  • RAYOS
  • ZYRTEC
  • ALAVERT, CLARITIN