HIVES

Hives

Hives are caused by an allergic reaction in the skin releasing the chemical histamine. Acute hives can usually be treated with medications but chronic hives, lasting longer than 6 months.

The skin condition we call 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. Hives Location

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% 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.

Hives Appearance

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.

Hives Cause

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.

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 and Histamine

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.

Acute and Chronic Hives

A distinction is made between acute hives and chronic hives. Acute hives last for less than 6 weeks, and chronic hives last for longer than 6 weeks. The designation of 6 weeks as the divider is arbitrary.

Acute Hives

Most investigators believe that acute hives occur as an allergic response to ingesting a food or drug. However, in 70% 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.

Chronic Hives

Hives that occur at least twice a week and have been present for more than 6 weeks are designated chronic. Unlike acute hives, chronic hives do not resolve quickly. In one study, 75% of people with chronic hives have symptoms for longer than 1 year, 50% have symptoms for longer than 5 years, and 20% have symptoms for decades. In 50% of the cases, the offending agent is not identified.

Diagnosis

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 Hives

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% 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 1 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.

Hives Treatments

The treatment of the physical hives is specific to the type that is diagnosed. In the majority of cases of chronic hives, the causative factor can not 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 2 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.

Causes of Hives

Overview of Causes of Hives

There are many causes of hives including foods, drugs, infections, and diseases. Oddly enough, even though there are many potential causes, in the majority of cases of hives, the cause is unknown. Hives causes can be broken down into 3 broad groups:

1. Idiopathic: This means we don't know the cause; it just happens.

2. Immunological: Some hives are caused by changes in the immune system. A typical scenario would be coming in contact with something that causes cells in the immune system to trigger the release of histamine from certain white blood cells called mast cells.

3. Nonimmunological: Exposure to certain substances can cause the direct release of histamine from mast cells without the involvement of other parts of the immune system.

 

If you have hives, you want to know what causes them so you can eliminate that trigger and free yourself from the itching. The following lists are not exhaustive, but do give the main known hives causes. While most cases of hives are idiopathic, see if you can eliminate any obvious causes of your hives. Just remember that it's best to talk to your healthcare provide before eliminating all possible hive triggers. If you suspect medication is causing your hives, contact your healthcare provider immediately.

Hives Causes by Medications

Antibiotics Heart Medication Pain Medication Others
Penicillins Beta-Blockers NSAID's * Radicontrast Dye
Amoxicillin Atenolol Naproxen  
Dicloxacillin Propanolol Ibuprofen  
Nafcillin Metoprolol Indomethacin  
Sulfas ACE Inhibitors Muscle Relaxers Dextran **
Bactrim Lsinopril Cyclobenzaprine  
Septra Fosinopril Methocartamol  
TMP-SMX Captopril Carisoprodol  
Cephalosporins Diuretics Codeine Quinine
Cephalexin Hydrochlorothiazide    
Ceftriaxone      
Tetracyclines Aspirin Morphine  
Minocycline      
Doxycycline      
Polymyxin      

* Nonsteroidal Anti-inflammatory Drugs
** Dextran is an IV fluid

 

Many medications can cause hives, but only about 10% of hives are caused by medications. Hives will most often occur in the first 36 hours after starting the medication, but hives can occur even after taking a medicine for a long time. You can see that antibiotics are a common culprit.

Hives caused by radiocontrast dye, codeine, morphine, and aspirin are usually not triggered by the immune system, rather these drugs cause the direct release of histamine from specialized white blood cells called mast cells.

Hives Causes by Diseases

When a cause for hives can be found, it's most likely an infection. Viral upper respiratory infections cause about 40% of hives rashes. Fortunately, these hives outbreaks resolve as the infection resolves. A chronic bacterial infection, especially sinusitis, may be the culprit if a case of hives is lingering.

The diseases listed above are rare causes of hives, with the exception of thyroid disease. People with chronic urticaria have a higher incidence of thyroid problems compared to the general population.

 
Diseases
Mastocytosis Dermatitis Herpetiformis
Amyloidosis Juvenile Rheumatoid Arthritis
Lymphoma Thyroid Disease
Rheumatic Fever Polycythemic Vera
Pemphigoid Lupus
Carcinomas  
Infections
Bacterial Chronic Bacterial
Gallbladder - Cholecystitis Sinusitis
H. Pylori - Ulcer Urinary Tract
Viral Other
Hepatitis B Intestinal Worms
Infectious Mononucleosis Malaria
Coxsackie Virus Infections  

Hives Causes by Foods

The Most Allergenic Foods
Chocolate Shellfish Nuts
Peanuts Pork Eggs
Tomatoes Strawberries Melons
Cheese Garlic Onions
Milk Spices  
May Cross-React With Latex
Chestnuts Bananas Passion Fruit
Avacado Kiwi  
Food Additives
Salicylates Citric Acid Tartrazine (a dye)
Benzoates Penicillin Egg
Fish Albumin Sulfites Yeast
 

This list shows the foods that most often cause hives. But an allergy to foods is actually pretty rare, occurring in 1% of hives sufferers. Whether the food additives listed above actually cause hives is controversial. But many people think their hives are caused by food additives and want to try eliminating them.

Many people have a sensitivity to latex which causes a contact dermatitis. The foods listed in the second table above contain chemicals that are similar enough to those found in latex that eating them can cause an allergic reaction. If you have a latex allergy, cross these foods off your shopping list.

Hives Treatments

The treatment of the physical hives is specific to the type that is diagnosed. In the majority of cases of chronic hives, the causative factor can not 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 2 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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