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Medically Reviewed On: July 11, 2006

Published on: February 20, 2008

Hives (known medically as urticaria) are smooth, raised, red, pink or white bumps of varying sizes that can appear suddenly anywhere on the body. They can cause discomfort and itching and can be made worse by scratching.

There are two kinds of hives:

• Allergic urticaria. Caused by the body’s overreaction to substances it encounters (allergic reaction).
• Nonallergic urticaria. Caused by factors other than an allergic reaction.

Individual hives usually last a few hours or a day and go away on their own. However, episodes can continue for varying periods of time. When hives occur deep in the skin, the condition is known as angioedema. There is no specific test to diagnose hives caused by allergic reactions or other factors. Diagnosis is based on:

• Close examination of the skin’s appearance and the eruptions themselves
• A detailed medical history, including exposure to potential allergens or irritants
• Ruling out disorders or diseases that may cause hives

The best treatment option for hives is to identify and remove the cause. Medications, such as antihistamines, may be recommended to relieve symptoms. However, treatment for hive-related conditions usually focuses on avoiding the situation or “trigger” that leads to an episode of hives. While they vary among individuals, these may include:

• Allergens (e.g., foods, pollens, pet dander, insect astings)
• Autoimmune diseases
• Infections
• Irritants (e.g., cosmetics)
• Other factors (e.g., extremes in temperatures, sunlight, tight-fitting clothing)

About hives

“Hives” is the common name of a skin disorder called urticaria in which itchy bumps of varying sizes appear suddenly anywhere on the body. Between 10 and 20 percent of the United States population will experience an episode of hives at some time in their life, according to the American Academy of Dermatology.

These skin eruptions form when blood plasma leaks out of small blood vessels in the skin, usually as a result of the release of chemicals called histamine. Histamine is released by mast cells (immune system cells) in response to a substance the body believes is harmful. Histamine causes the blood vessels to widen and leak fluid into the surrounding tissue, resulting in redness, swelling and an itching sensation. Allergic reactions, chemicals, foods and medications are all potential triggers for histamine release.

Hives vary greatly in their appearance and an individual hive may also be referred to as a wheal. They can appear anywhere on the body, but most commonly show up on the arms and legs. They are not as common on the palms of the hands or the soles of the feet. Sometimes individual hives join together to form one giant hive. In some cases, hives may be restricted to one area of a person’s body. In other instances, individuals may experience widespread eruptions.

Hives eventually fade, lasting from a few minutes to a few hours. However, new hives may erupt as others disappear several times during episodes. Therefore, although individual hives usually last less than 24 hours, an episode of recurring hives can continue for varying periods. The length of these periods determines if the condition is considered chronic or acute, as follows:

• Acute hives (acute urticaria). Episodes that last for less than six weeks. Acute urticaria usually persists for a few days and is often caused by an allergic reaction to food or a drug. Other potential causes include infections, insect bites, internal disease, pressure on the skin, cold or sunlight.
• Chronic hives (chronic urticaria). Episodes that occur at least twice a week and persist for more than six weeks. According to the American Academy of Allergy, Asthma and Immunology, about 50 percent of patients have symptoms for more than six months and 20 percent exhibit symptoms for over a decade. The cause of chronic hives is often much more difficult to diagnose than that of acute hives and therefore is often not identified. Chronic hives are twice as common in women as in men.

Allergic urticaria may occur when an allergen is inhaled, ingested or comes into direct contact with a person’s skin. But not all hives are the result of an allergic reaction. They can also be caused by:

• Constant pressure on the skin, such as with a belt or shoulder strap
• Environmental factors, such as extremes in temperatures
• Irritating chemicals or cosmetics applied to the skin, even if the person is not allergic to these substances
• Infection

Although hives generally cause only discomfort and itching, in rare cases serious swelling occurs in the mouth or throat. Swelling may be severe enough to restrict the person’s ability to breathe and lead to a loss of consciousness. Hives that impair breathing or swallowing require emergency medical attention.

Hives often occur simultaneously with a related but more serious skin disorder called angioedema. Angioedema produces a deeper swelling in the skin, usually around the face, tongue, extremities or genitals. It can lead to death if untreated.

Types and differences of hives

Hives (urticaria) may be caused by allergic or nonallergic reactions. Allergic urticaria occurs when the body misinterprets a substance (allergen) as being a threat and then attacks that threat (allergic reaction). It is the less common form of hives, and it is seen more often in children than adults.

When a definitive allergic basis cannot be found or proven, hives are classified as nonallergic. Exposure to extreme temperatures, repeated stroking of the skin, psychological stress, reaction to diseases and frequent bacterial and viral infections are examples of nonallergic urticaria. Women in the last trimester of pregnancy may experience hives, which usually resolve after delivery.

Urticaria is often classified according to the cause and/or length of time the episodes last. Examples include:

• Acute urticaria. Episodes of hives that last for less than six weeks. Most episodes of allergic hives are acute and persist for a few days after exposure to the allergen.
• Aquagenic urticaria. Hives caused by contact with water.
• Cholinergic urticaria. Hives caused by exercise, passive body warming (shower or bath) or emotional stress. The wheals (individual hives) usually occur around the lips or larynx, although they can appear anywhere on the skin. These hives are generally the smallest type seen, appearing on the skin like goosebumps. This allergic reaction can also lead to lung symptoms, such as shortness of breath.
• Chronic idiopathic urticaria. Episodes of hives that persist for more than six weeks (chronic) for which the cause is unknown (idiopathic). Seen most often in middle-aged women, but can affect all ages, genders and races. Chronic, idiopathic urticaria can persist for years and has been traditionally believed to be nonallergic. However, recent research indicates that some patients develop an allergy to components in their own skin, continuously triggering hives. Researchers hope their findings will lead to better understanding of the causes of chronic idiopathic urticaria.
• Cold urticaria. Hives caused by cold temperatures.
• Contact urticaria. A form of allergic urticaria caused when the skin comes in direct contact with an allergen (e.g., in a person with a latex allergy, it may be caused by wearing latex gloves).
• Pressure urticaria. Hives caused by pressure on the skin. There are two main forms: Dermatographism involves wheals that form in areas where clothing applies friction to the skin. Delayed pressure urticaria involves wheals that form under belts, shoulder straps or bras and are more diffuse in appearance.
• Solar urticaria. Hives caused by direct exposure to the sun. Wheals may appear within minutes of sun exposure (photosensitivity).
• Vasculitic urticaria (urticarial vasculitis). Hives that stay in the same place for more than a day and that leave a pigmented bruise mark when the swelling has resolved. Vasculitic urticaria may be part of an illness, such as rheumatoid arthritis, which also affects other parts of the body.
• Exercise-induced anaphylaxis. A related condition, which may be triggered by a combination of physical exertion and the eating of certain foods. It is differentiated from cholinergic urticaria by the structure of the lesions and the degree of response to passive body warming.

These different types of hives often coexist, further complicating a diagnosis. For instance, cold urticaria and pressure urticaria often occur together. The presence of some types of urticaria may mean a patient has a higher risk of developing some type of autoimmune thyroid disease.

Potential causes of hives

Hives (urticaria) are a reaction of the skin to a number of factors that lead to the chemical histamine being released into the body. Histamine, in turn, causes blood plasma in the small blood vessels of the skin to leak out into the surrounding tissue. The plasma is what causes the symptoms of red, swollen, itchy skin associated with hives.

The following factors may cause urticaria:

• Blood transfusions
• Cosmetic allergies or irritants
• Drug allergies, reactions or side effects
• Emotional factors, such as stress
• Environmental factors, such as exposure to sun or extreme cold/heat
• Fever, infections and infestations
• Food allergies, especially to eggs, shellfish, nuts, chocolate, milk and fruits
• Indoor and outdoor allergies, such as to pollen, mold or animal dander
• Insect bites
• Pressure or friction on the skin
• Systemic and general diseases, such as hepatitis, lupus and mononucleosis

In addition, the likelihood of developing hives may be inherited. A patient with a family medical history of hives is more likely to develop hives themselves. Acute hives are more commonly seen in young people, and causes often include allergies to food and food additives and certain medications. The cause of chronic hives is harder to determine. Some experts estimate that the cause of chronic hives is only identified in 25 percent of cases.

Signs and symptoms of hives

Hives (urticaria) can erupt unexpectedly but can disappear just as suddenly. It can be difficult to recognize hives because they vary greatly in their appearance. They may be:

• Alone or in batches
• Arranged randomly or in a vertical row
• Burning, stinging or itching
• Circular or irregularly shaped
• Red, pink or white
• Slightly raised or flat and smooth
• Varying sizes (as small as a pencil eraser or as large as a basketball)

Unlike other skin rashes, hives are not flaky. An individual hive (called a wheal) also differs from a blister, which has a loose membrane over liquid. Wheals usually remain less than a half-inch (1 centimeter) across. Those that are larger (up to 4 inches across, or 10 centimeters) may look like rings of redness with a pale center. Wheals cannot break apart and liquid does not ooze out. They generally cluster and rise in one area and then wane only to reappear in a batch somewhere else on the body. Wheals can change shape and disappear or reappear within minutes or hours.

The most frequent complaint is the annoying itch that accompanies wheals, but they can also cause a burning or stinging sensation. The eruptions may be so intense that they lead to extreme irritability and sleeplessness.  

Most hives are white or red welts that are surrounded by a red patch (called a flare) on the skin’s surface, quite often where clothes touch the skin. Deep swelling beneath the skin that appears on the face, tongue, extremities or genitals is a related condition called angioedema. Angioedema, though related to hives, has a different appearance:

• Eyes may appear swollen closed
• Skin surface may appear normal (no hives or rash)
• Swellings may appear the same on both sides of the body
• Swellings usually do not itch, but may cause pain or a burning sensation

Hives are rarely life-threatening, and acute cases usually disappear on their own. However, more severe reactions may accompany hives or angioedema. Potentially life-threatening reactions are called anaphylaxis and require immediate medical care. They include:

• Difficulty breathing and swallowing
• Dizziness or faintness
• Loss of consciousness
• Rapid or abnormal heartbeat
• Swelling of the face, tongue or throat

Diagnosis methods for hives
A single outbreak of hives (urticaria) that resolves without treatment probably does not need a formal evaluation. However, patients with recurrent episodes should see their physician.

No single laboratory test can isolate the specific cause of hives, but there are a number of tests available to identify or rule out certain triggers. A medical history and complete physical examination will provide the best clues as to the cause(s) of an individual’s hives. Questions may address the following:

• Any allergies a patient or a family member may have
• Anyone else in the family or the household who may have hives
• New or unfamiliar soaps, detergents, cosmetics and foods the patient may be using
• Recent illnesses, both acute and chronic
• Types of medications currently being taken or recently stopped taking
• Whether the patient is pregnant or suspects pregnancy

Some conditions can have rashes associated with them and may be ruled out before a diagnosis of allergic urticaria is reached, including:

• Joint inflammation. Rheumatoid arthritis produces bumps under the skin.
• Lupus.  Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown origin that affects the bones and internal organs. Almost half of SLE patients have a classic malar rash (pertaining to the cheekbone) specific to SLE.
• Respiratory diseases. Diseases of the lung that impair breathing. Microbial infections such as mold exposure and meningitis have skin rashes associated with them.
• Malignancies. Cancerous growths or tumors. Rashes and other dermatologic conditions can signal the presence of cancer in the body.

Diagnosis of hives is based on the appearance of the skin and, in the case of allergic urticaria, can be confirmed by the history of exposure to allergens. In some instances, skin tests, blood tests or urine tests may be performed to determine which allergens are triggering episodes of hives or to determine other potential causes.

However, it should be noted that although the cause of acute hives can often be identified, chronic hives usually cannot be definitively diagnosed. Only about 25 percent of cases of chronic hives are identified, according to the American Academy of Allergy, Asthma and Immunology.

Treatment and prevention of hives
Hives (urticaria) that cause difficulty breathing or swallowing require emergency medical attention. Mild cases of acute hives may not require treatment. They often appear suddenly and subside without treatment within days or even minutes. Wheals (individual hives) that appear suddenly in children before disappearing quickly without recurring usually indicate the presence of a viral infection. For this reason, parents of children with this type of hives should consult a physician.

When treatment is necessary, the best method is to find and address the underlying cause. If a specific food is suspected, it should not be ingested. Keeping a food diary and closely reading food packaging labels can help identify the substance(s) that cause hives.

Patients with solar urticaria need to apply sunscreen when outside and wear protective clothing. Vigorous drying with a towel after a bath should be avoided as well as harsh soaps and frequent bathing to reduce dry skin in those people susceptible to hives. Other treatment options include:

• Avoiding activity that causes sweating.
• Staying calm.
• Taking cool baths or using cold compresses to reduce swelling and discomfort.
• Wearing loose, comfortable clothing. Tight clothing can trigger a new outbreak.
• Avoiding hot baths or showers following an outbreak. These can trigger a recurrence.

After an episode of allergic urticaria, medications called antihistamines may be recommended to relieve symptoms. Antihistamines block the release of histamines into the body, which occurs as the result of an allergic reaction. Older antihistamines used to cause drowsiness but there are newer ones on the market that cause little or no drowsiness.

Specific drugs that have proven success in treating hives are:

• Short-acting H1 antihistamines. The primary medications for mild cases of hives. They are available over-the-counter and are inexpensive. However, they may cause drowsiness.
• Long-acting H1 antihistamines. These are available only by prescription and are more expensive. However, they usually do not cause sleepiness and need be taken less frequently.
• Corticosteroids. Drugs that suppress the allergic response of the immune system. They relieve the inflammation and swelling symptoms and lessen the chance of the eruption recurring. Because they may cause serious side effects, corticosteroids usually are prescribed only for severe symptoms when other treatments are ineffective and are given for as short a time as possible.
• Epinephrine. An emergency treatment measure used for anaphylactic shock and most other severe allergic reactions that may include hives. This drug is usually administered via an injection. Patients at high risk for severe attacks may be advised to always carry epinephrine shots with them and learn how to self-administer the medication. Epinephrine injections may also be administered in an emergency room setting.
• Antidepressants. Tricyclic antidepressants (e.g., doxepin) are also a potent antihistamine that may help relieve chronic hives. These drugs may cause a sedative effect in some patients and may have other side effects, such as blurred vision, urine retention and dry mouth.

In addition, a number of medications are currently being studied for potential use in the treatment of hives. These include:

• H1 and H2 blocking drugs. Medications not yet approved by the U.S. Food and Drug Administration (FDA) for treating hives. Studies have found these medications effective in patients who do not respond to H1 or H2 type antihistamines.

• H2 antihistamines. These medications have been found to reduce the redness and swelling when given in conjunction with H1 antihistamines. They were originally developed to treat ulcers and have not yet been approved by the FDA for the treatment of hives.

Other treatment and prevention methods depend on the source of the hive reactions. For instance, in solar urticaria, sunscreen creams and general sun protection are recommended. Some patients require sunscreen creams with zinc or titanium oxide to completely block the sun’s rays.  

Questions for your doctor regarding hives
Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following hives–related questions:

1. What are the characteristic features of hives?

2. What causes hives?

3. Do hives spread?

4. How long does an outbreak usually last?

5. How dangerous are hives to my health?

6. What are my treatment options?

7. Will I have hives my whole life?

8. Is one area of my body more prone to hives than another?