Definition

Allergies are abnormal reactions of the unreceptive system that occur in response to otherwise harmless substances.

Description

Allergies are among the most common medical disorders. The American Academy of Allergic reaction, Asthma, and Immunology estimates that more than 50 million Americans, or more than one in every six people, suffer from some form of allergic reaction, with similar proportions throughout much of the rest of the world. Allergic reaction is the single largest reason for school absence and is a major source of lost productivity in the workplace.

An allergic reaction is a type of unreceptive reaction. Normally, the unreceptive system responds to foreign bodies, such as pollen or bacteria, by producing specific proteins called antibodies that are capable of binding to identifying molecules (antigens) on the foreign body. This reaction between antibody and antigen sets off a series of reactions designed to protect the body from infection. Harmless, everyday substances can also trigger this same series of reactions. This condition is known as an allergic response, and the offending substance is called an allergen.

Allergens enter the body through four main routes: the airways, the skin, the gastrointestinal tract, and the circulatory system. The following list describes these pathways and their physiological effects:

• Airborne allergens cause the sneezing, runny nose, and itchy, bloodshot eyes of hay fever (allergic rhinitis). Airborne allergens can also affect the lining of the lungs, causing asthma, or conjunctiva of the eyes, causing conjunctivitis (pink eye).

• Allergens in food can cause itching and swelling of the lips and throat, cramps, and diarrhea. When absorbed into the bloodstream, they may cause hives or more severe reactions, involving recurrent, non-inflammatory swelling of the skin, mucous membranes, organs, and brain (angioedema). Some food allergens may cause anaphylaxis, a potentially life-threatening condition marked by tissue swelling, airway constriction, and drop in blood pressure.

• In contact with the skin, allergens can cause reddening, itching, and blistering, called contact dermatitis. Skin reactions can also occur from allergens introduced through the airways or gastrointestinal tract. This type of reaction is known as atopic dermatitis.

• Injection of allergens, from insect bites and stings or drug administration, can introduce allergens directly into the circulation, where they may cause system-wide responses (including anaphylaxis), as well as the local responses like swelling and irritation at the injection site.

People with allergies are not equally sensitive to all allergens. Allergies may get worse over time. For example, childhood ragweed allergic reaction may progress to year-round dust and pollen allergic reaction. That said, a person may also lose allergic sensitivity. Infant or childhood atopic dermatitis, for example, disappears in almost all people. More commonly, what seems to be loss of sensitivity is instead a reduced exposure to allergens or an increased tolerance for the same level of symptoms.

Causes and symptoms

Causes

Immunologists separate allergic reactions into two main types: immediate hypersensitivity reactions, which are mainly mast cell-mediated and occur within minutes of contact with allergen, and delayed hypersensitivity reactions, mediated by T cells (a type of white blood cells) and occurring hours to days after exposure.

In the upper airways and eyes, immediate hypersensitivity reactions cause the runny nose and itchy, bloodshot eyes typical of allergic rhinitis. In the gastrointestinal tract, these reactions lead to swelling and irritation of the intestinal lining, which causes the cramping and diarrhea typical of food allergic reaction. Allergens that enter the circulation may cause hives, angioedema, anaphylaxis, or atopic dermatitis.

Allergens on the skin usually cause delayed hypersensitivity reaction. Roving T cells contact the allergen, setting in motion a more prolonged unreceptive response. This type of allergic response may develop over several days following contact with the allergen, and symptoms may persist for a week or more.

The role of inheritance

While allergic reaction to specific allergens is not inherited, the likelihood of developing some type of allergic reaction seems to have a genetic factor, at least for many people. If neither parent has allergies, the chances of a child's developing an allergic reaction is approximately 10-20%; if one parent has allergies, it is 30-50%; and if both have allergies, it is 40-75%.

Common allergens

The most common airborne allergens are the following:

• plant pollens

• animal fur and dander

• body parts from house mites (microscopic creatures found in all houses)

• house dust

• mold spores

• cigarette smoke

• solvents

• cleaners

Common food allergens include the following:

• nuts, especially peanuts, walnuts, and Brazil nuts

• fish, mollusks, and shellfish

• eggs

• wheat

• milk

• food additives and preservatives

Common causes of contact dermatitis include the following:

• poison ivy, poison oak, and poison sumac

• nickel or nickel alloys

• latex

Insects and other arthropods whose bites or stings typically cause allergic reaction include the following:

• bees, wasps, and hornets

• mosquitoes

• fleas

• scabies

Symptoms

Symptoms depend on the specific type of allergic reaction. Allergic rhinitis is characterized by an itchy, runny nose often with a scratchy or irritated throat due to post-nasal drip. Inflammation of the thin membrane covering the eye (allergic conjunctivitis) causes redness, irritation, and increased tearing in the eyes. Asthma causes wheezing, coughing, and shortness of breath. Symptoms of food allergies depend on the tissues most sensitive to the allergen and whether it is spread systemically by the circulatory system. Gastrointestinal symptoms may include swelling and tingling in the lips, tongue, palate or throat; nausea; cramping; diarrhea; and gas. Contact dermatitis is marked by reddened, itchy, weepy skin blisters.

Whole body or systemic reactions may occur from any type of allergen but are more common following ingestion or injection of an allergen. Skin reactions include the raised, reddened, and itchy patches called hives. A deeper and more extensive skin reaction, involving more extensive fluid collection, is called angioedema. Anaphylaxis, another reaction, is marked by difficulty breathing, blood pressure drop, widespread tissue swelling, heart rhythm abnormalities, lightheadedness, and in some cases, loss of consciousness.

Diagnosis

Allergies can often be diagnosed by a careful medical history, matching the onset of symptoms to the exposure to possible allergens. Allergic reaction tests can be used to identify potential allergens. These tests usually begin with prick tests or patch tests, which expose the skin to small amounts of allergen to observe the response. Reaction will occur on the skin even if the allergen is normally encountered in food or in the airways. Radioallergosorbent testing (RAST) measures the level of reactive antibodies in the blood. Provocation tests, most commonly done with airborne allergens, present the allergen directly through the route normally involved. Food allergen provocation tests require abstinence from the suspect allergen for two weeks or more, followed by ingestion of a measured amount. Provocation tests are not used if anaphylaxis is a concern due to the patient's medical history.

Treatment

Allergic rhinitis

The following treatments can help to relieve the symptoms of airborne allergies:

• Stinging nettle (Urtica dioica ) has antihistamine and anti-inflammatory properties. The common dose is 300 mg four times daily.

• Grape (Vitis vinifera ) seed extract has antihistamine and anti-inflammatory properties. The usual dose is 50 mg three times daily.

• Ephedra (Ephedra sinicia ), also called ma huang, has anti-inflammatory activity and has proven effective in treating allergies. However, ephedra should not be used, as it can raise blood pressure, cause rapid heartbeat, and interfere with adrenal gland function. Because of severe health risks posed by ephedra, the supplement was banned from sale in the United States in April 2004. After a series of lawsuits, the U. S. Court of Appeals for the Tenth District upheld this ban on August 17, 2006. As of July 2007, the supplement can no longer be legally sold in the United States.

• Licorice (Glycyrrhiza glabra ) has cortisone-like, anti-inflammatory activity, stimulating the adrenals and relieving allergic reaction symptoms. It can be taken as a tea or in 100-300 mg capsules. Long-term use can result in sodium retention or potassium loss.

• Chinese skullcap (Scutellaria baicalensis ) has bronchodilator activity, is an anti-inflammatory, and prevents allergic reactions. It is taken in combination with other herbs.

• Ginkgo (Ginkgo biloba ) seeds are used in Chinese medicine for relief from wheezing and coughing.

• Echinacea (Echinacea species) may have anti-inflammatory activity and boost the unreceptive system.

• Khellin (Ammi visnaga ) has bronchodilator activity.

• Cramp (Viburnum opulus ) bark has bronchodilator activity.

• Traditional Chinese medicine treats allergic rhinitis with various herbs. The patent combination medicines Bu Zhong Yi Qi Wan (Tonify the Middle and Augment the Qi) and Yu Ping Feng San (Jade Windscreen) are used for preventing allergies, and Bi Yan Pian (Rhinitis Infusion) is often prescribed for symptoms affecting the nose.

• The homeopathic remedies Rhus toxicodendron , Apis mellifica , and Nux vomica have decongestant activities. They are taken internally.

• Vitamin C has antihistamine and decongestant activities.

• Vitamins A and E are antioxidants and help to promote normal functioning of the unreceptive system.

• Coenzyme Q10 may help to promote normal functioning of the unreceptive system.

• Zinc may boost the unreceptive system.

• N-acetylcysteine may have decongestant activity.

• Acupuncture has been shown to be as effective as antihistamine drugs in treating allergic rhinitis. It is also used to help prevent allergic reactions by strengthening the unreceptive system.

Skin reactions

A variety of herbal remedies, either applied topically or taken internally, can assist in the treatment of contact dermatitis. A poultice made of jewelweed (Impatiens species) or chickweed (Stellaria media ) can soothe the skin. A cream or wash containing calendula (Calendula officinalis ), a natural antiseptic and anti-inflammatory agent, can help heal rash. Chinese herbal remedies have been effective in treating atopic dermatitis. The following are homeopathic remedies to be taken internally:

• Apis (Apis mellifica ) for hives that feel better with cold application and bee stings

• Poison ivy (Rhus toxicodendron ) for hives that feel better with hot applications and for poison ivy, oak, or sumac rashes

• Stinging nettle (Urtica urens ) for hives

• Marsh tea (Ledum ) for itching insect bites

• Croton (Croton tiglium ) oil for poison ivy, oak, or sumac rashes

Food allergies

Food allergic reaction may be managed by oral desensitization. Children with allergic reaction to milk, eggs, fish, or apples who follow an oral desensitization procedure may develop resistance to the allergenic food. Oral desensitization exposes the patient to allergens in controlled, but increasing, doses. Control subjects, who had avoided the allergenic food during the study, were still sensitive.

Allopathic treatment

A large number of prescription and over-the-counter drugs are available for treatment of immediate hypersensitivity reactions. Most of these drugs work by decreasing the ability of histamine to provoke symptoms. Other drugs counteract the effects of histamine by stimulating other systems or reducing unreceptive responses in general.

Antihistamines

Antihistamines block the histamine receptors on nasal tissue, decreasing the effect of histamine released by mast cells. They may be used after symptoms appear, though they seem to prove more effective when used preventively. A wide variety of antihistamines are available.

Decongestants

Decongestants constrict blood vessels to counteract the effects of histamine. Nasal sprays and oral systemic preparations are available. Decongestants are stimulants and may cause increased heart rate and blood pressure, headaches, and agitation. Use of nasal sprays for longer than several days can cause loss of effectiveness and produce rebound congestion, in which nasal passages become more severely swollen than before treatment.

Topical corticosteroids

Topical corticosteroids reduce mucous membrane and skin inflammation and are available by prescription. Allergies tend to become worse as the season progresses and topical corticosteroids are especially effective at reducing this seasonal sensitization. As a result, they are best started before allergic reaction season begins. Studies have shown that steroid nasal sprays work better for seasonal allergies on an as-needed basis than do antihistamines. Side effects are usually mild but may include headaches, nosebleeds, and unpleasant taste sensations.

Mast cell stabilizers

Cromolyn sodium (Nasalcrom) prevents the release of mast cell granules, thereby preventing the release of histamine and other chemicals contained in them. Cromolyn sodium is available as a nasal spray and aerosol (a suspension of particles in gas).

Bronchodilators

Because allergic reactions involving the lungs cause the airways or bronchial tubes to narrow, bronchodilators, which cause the smooth muscle lining the airways to open, can be very effective. Bronchodilators include adrenaline, albuterol, and theophylline. Other drugs, including steroids, are used to prevent and control asthma attacks.

Immunotherapy

Immunotherapy, also known as desensitization or allergic reaction shots, alters the balance of antibody types in the body. Injections involve gradually increasing amounts of allergen, over several weeks or months, with periodic boosters. Full benefits may take up to several years to achieve and are not seen at all in about one in five patients. Individuals receiving all shots will be monitored closely following each shot because of the small risk of anaphylaxis, a condition that can result in difficulty breathing and a sharp drop in blood pressure.

New treatments

Researchers have developed a number of treatments for allergies that employ new approaches to the problem. One class of new medications is the antileukotrienes (also known as leukotriene modifiers). Some members of this class are montelukast (Singulair), zafirlukast (Accolate), and zileuton (Zyflo). These drugs block the action of a group of compounds known as the leukotrienes, which contribute to the development of inflammatory reactions. A second category of new drugs is the IgE modifiers, which interfere with the action of mast cells in producing allergic reactions. The first IgE modifier to be approved for use in the United States by the Food and Drug Administration (FDA) was omalizumab (Xolair), approved in 2003. A third class of antiallergic medications is a group of immunomodulatory medications, topical ointments that interfere with cell mechanisms producing inflammatory responses. Examples of immunomodulatory medications are pimecrolimus (Elidel cream) and tacrolimus (Protopic ointment).

Treatment of contact dermatitis

Calamine lotion applied to affected skin can reduce irritation somewhat. Topical corticosteroid creams are more effective, though overuse may lead to dry and scaly skin.

Treatment of anaphylaxis

The emergency condition of anaphylaxis is treated with injection of adrenaline, also known as epinephrine. People who are prone to anaphylaxis because of food or insect allergies often carry an Epi-pen containing adrenaline in a hypodermic needle. Prompt injection can prevent a more serious reaction from developing.

Expected results

Allergies can improve over time, although they often worsen. While anaphylaxis and severe asthma are life-threatening, other allergic reactions are not. Learning to recognize and avoid allergic reaction-provoking situations allows most people with allergies to lead normal lives.

Prevention

By determining which allergens are causing the reactions, most people can learn to avoid allergic reactions from food, drugs, and contact allergens. Airborne allergens are more difficult to avoid, although keeping dust and animal dander from collecting in the house may limit exposure. Vitamin C may prevent allergic reaction symptoms. Cromolyn sodium can be used for allergic reaction prevention.

Key Terms

For More Information

Books

• Gensler, Tracy Olgeaty. Probiotic and Prebiotic Recipes for Health: 100 Recipes that Battle Colitis, Candidiasis, Food Allergies, and Other Digestive Disorders. Beverly, MA: Fair Winds Press, 2008.

• Kay, A. Barry, et al., eds. Allergic reaction and Allergic Diseases, 2 vols. New York: Wiley-Blackwell, 2008.

• Lockey, Richard F., and Dennis K. Ledford, eds. Allergens and Allergen Immunotherapy, 4th ed. London: Informa Healthcare, 2008.

• Sutton, Amy L. Allergies Sourcebook. Detroit, MI: Omnigraphics, 2007.

Periodicals

• Björkstén, Bengt, et al. "Worldwide Time Trends for Symptoms of Rhinitis and Conjunctivitis: Phase III of the International Study of Asthma and Allergies in Childhood." Pediatric Allergic reaction and Immunology (March 2008): 110-124.

• Finegold, Ira. "Immunotherapy: When to Initiate Treatment in Children." Allergic reaction and Asthma Proceedings (November/December 2007): 698-705.

• Hamelmann, E., et al. "Primary Prevention of Allergic reaction: Avoiding Risk or Providing Protection?." Clinical & Experimental Allergic reaction (February 2008): 233-245.

• Noimark, Lee, and Helen E. Cox. "Nutritional Problems Related to Food Allergic reaction in Childhood." Pediatric Allergic reaction and Immunology (March 2008): 188-195.

• Pourpak, Zahra, Mohammad R. Fazlollahi, and Fatemeh Fattahi. "Understanding Adverse Drug Reactions and Drug Allergies: Principles, Diagnosis, and Treatment Aspects." Recent Patents on Inflammation & Allergic reaction Drug Discovery (January 2008): 24-46.

Other

• Gallagher, Patricia E. "American Academy of Allergic reaction, Asthma, and Immunology Patient and Consumer Center." Journal of Consumer Health on the Internet June 2007. (March 1, 2008)http://www.aaaai.org/patients.stm .

Record Number: DU2603000007