What Are the Causes, Symptoms and Treatment for Hives?

Why antihistamines provide relief for this itchy problem

The hives skin rash.
The hives skin rash. gokhan ilgaz/Getty Images

The skin condition commonly called hives is referred to in medical terms as urticaria. A hive, or wheal, is a symptom of urticaria. However, most people do not develop one hive when they have urticaria, hence the name hives.

The Location and Appearance of Hives

Urticaria is a common condition that can affect any person of any race at any age in any season of the year. It occurs in up to 20 percent of the population at one time or another.

Hives can occur on any skin surface, but usually spare the palms and soles of the feet. Hives are classified as acute or chronic depending on the length of the episode.

A hive, or wheal, is a circular, red, spongy lesion that evolves and changes over minutes to hours. It is usually surrounded by an area of redness called a flare. Hives can vary in size from a few millimeters to giant hives covering a whole extremity.

What Causes Hives

Hives result from dilation of capillaries allowing fluid to leak out into the surrounding tissue, the epidermis. They resolve when the body absorbs this fluid. The border of a hive is described as polycyclic, or made up of many circles, and changes as fluid leaks out and then is absorbed. Pressing on a hive causes the skin to blanch distinguishing it from a bruise or papule.

Angioedema

A condition called angioedema occurs when capillaries dilate and leak fluid deeper into the skin, into the dermis and subcutaneous tissue.

Angioedema typically causes swelling of the lips, larynx (producing hoarseness or shortness of breath), or the lining of the stomach and intestines (causing abdominal pain). Many times angioedema occurs with an episode of hives.

Why Hives Itch

Hives are itchy because the swelling occurs in the epidermis, which has many nerve endings.

The intensity of the itching varies from person to person and episode to episode. Angioedema typically does not itch since it involves swelling in deeper structures where there are fewer nerve endings.

Hives occur in response to a complicated chain of events that leads to the release of a chemical called histamine into the skin. Histamine is located in certain white blood cells called mast cells, which are most abundant in the skin around capillaries. If properly triggered, these mast cells release granules of chemicals, the most powerful of which is histamine.

Histamine causes the cells making up the blood vessels to contract allowing fluid to leak out of the blood vessel. Red blood cells are too large to leak out of these "holes." Injecting histamine into the skin causes a triple response of redness, leaking of fluid producing a hive, and the flare or redness around the hive.

A distinction is made between acute hives and chronic hives. Acute hives last for less than six weeks, and chronic hives last for longer than 6 weeks.

The designation of six weeks as the divider is arbitrary.

Acute and Chronic Hives

Most investigators believe that acute hives occur as an allergic response to ingesting a food or drug. However, in 70 percent of cases, the cause is not found. Acute hives usually resolve on their own. Extensive laboratory investigations are not necessary and do not yield much information. Acute hives are treated with antihistamines, which work by blocking the release of histamine from mast cells.

It is important to take the antihistamines regularly because once the histamine is released, they have no affect. Over-the-counter antihistamines work well but have the side effect of sedation. The newer prescription antihistamines are also effective and do not cause drowsiness.

Hives that occur at least twice a week and have been present for more than six weeks are designated chronic. Unlike acute hives, chronic hives do not resolve quickly. In one study, 75 percent of people with chronic hives have symptoms for longer than a year, 50 percent have symptoms for longer than five years, and 20 percent have symptoms for decades. In 50 percent of the cases, the offending agent is not identified.

Diagnosing Hives

Diagnosing chronic hives is more involved than diagnosing acute hives. A very detailed history is taken to determine the exact appearance and duration of the hives. A food diary should be kept, and all medications documented. The time course of the hives should also be covered. For example, do the symptoms persist when not at work or while on vacation at a different location?

Some chronic hives are caused by infections that were not realized, especially sinus infections. Chronic hives are also associated with thyroid disease -- hypothyroidism and hyperthyroidism. An infection with the yeast, Candida albicans, is also associated with chronic hives. All of these conditions should be ruled out. Skin testing is of variable benefit since people with hives tend to react positively to most agents tested for.

Physical Urticaria

A subset of chronic hives is known as physical urticaria. This means that a specific physical stimulus causes hives in certain people. Physical hives cause up to 16 percent of chronic hives. A general description of each type of physical hives is given here, and a more detailed description is given separately.

  • Dermographism - Hives are produced suddenly by rubbing or stroking the skin. This type of physical hives is very common.
  • Pressure Urticaria - Hives are produced several hours after applying pressure to the skin. This is a fairly common form of hives and difficult to diagnose since the hives develop hours after contact with the skin.
  • Cholinergic Urticaria - Hives are produced during or shortly after exercise. This is a very common type of hives.
  • Exercise Induced Anaphylaxis - People with this disorder develop hives, shortness of breath, and dizziness after exercising. Some people with this condition may pass out or go into shock. This condition is very rare and was only first described in 1980.
  • Cold Urticaria - Hives are produced with a sudden drop of temperature or exposure to cold water or ice. This is a frequent cause of hives.
  • Solar Urticaria - Hives occur minutes after exposure to the sun and disappear within one hour. This is a fairly frequent cause of hives.
  • Heat Urticaria - Hives occur within minutes after exposure of the skin to a warm stimulus. This type of hives is very rare.
  • Vibratory Angioedema - Angioedema is produced after exposure of the skin to vibration. This is also a very rare type of hives.
  • Aquagenic Urticaria - Hives are produced immediately after exposure of the skin to water. This form of hives is also very rare.

Treating the Various Forms of Hives

The treatment of physical hives is specific to the type that is diagnosed. In the majority of cases of chronic hives, the causative factor cannot be determined. For these people, antihistamines are the mainstay of treatment.

As with acute hives, antihistamines must be taken regularly to prevent the release of histamine. The older antihistamines, such as Benadryl, can cause sleepiness when starting therapy. After about two weeks, the sleepiness generally improves or resolves. However, the therapeutic effect of antihistamines does not diminish with regular use. In other words, a person does not develop a tolerance for antihistamines requiring higher doses to stop histamine release. The newer antihistamines, such as Zyrtec, Claritin, and Allegra, do not cause as much sleepiness and are also effective in treating hives.

Sometimes medications such as cimetidine or ranitidine, usually used to reduce stomach acid secretion, are used with antihistamines. These medications are also antihistamines, but they block a different histamine receptor. A medication called doxepin is a tricyclic antidepressant, or TCA. It also powerfully blocks histamine release and may be used in conjunction with other medications. Its main side effect is also sleepiness.

Oral steroids like prednisone and medrol are considered for cases of hives that don't respond to antihistamines. Epinephrine is used for severe cases of hives. Epinephrine is a powerful blocker of histamine release and has a rapid onset of effect, but also lasts only a short amount of time in the body.

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