ALLERGIES


DEFINITION

Allergies are abnormal reactions of the immune system to substances that are otherwise harmless.

DESCRIPTION

Allergies are among the most common medical disorders. By some estimates more than one in every five Americans suffer from some form of allergy. This statistic holds true throughout the world. Allergies are the single most common reason for absence from school, and they are the major cause of hours lost from work.

An allergy is a type of immune reaction. Normally, the immune system protects the body against harmful invaders, like bacteria and viruses. These invaders carry distinctive markers on their outside surface called antigens (pronounced an-TIH-juns). The immune system produces special molecules called antibodies when it finds an antigen. The antibodies attach themselves to the antigens. The antigen-antibody combination sets off a series of changes in the body, which protect the body from infection and disease.

This same sequence of events can also occur with harmless invaders, such as dust and pollen. This response by the immune system is known as an allergy. The markers on the otherwise harmless invaders are known as allergens (pronounced AL-er-jins).

Allergies: Words to Know

Allergen:
A substance that causes an allergic reaction.
Anaphylaxis:
An increased sensitivity to an allergen causing dilation (expansion) of blood vessels and tightening of muscles. Anaphylaxis can result in sharp drops in blood pressure, difficulty in breathing, and death if left untreated.
Antibody:
A chemical produced by the immune system in response to an antigen.
Asthma:
A lung condition in which airways become narrowed, causing wheezing, coughing, and shortness of breath.
Contact dermatitis:
Inflammation of the skin caused by exposure to an allergen.
Histamine:
A chemical released by mast cells that causes cells to become leaky and irritates nerve cells, causing pain.
Mast cells:
A type of cell that makes up the immune system that releases histamine when stimulated by immunoglobin type E, a molecule released by white blood cells.

Allergens can enter the body through four main routes: the nose and mouth, the gastrointestinal (digestive) tract, the skin, and the circulatory (blood) system.

  • Allergens in the air can cause hay fever (see hay fever entry), asthma (pronounced AZ-muh; see asthma entry), or conjunctivitis (pink eye; see conjunctivitis entry).
  • Allergens in food can cause itching and swelling of the lips and throat, cramps, and diarrhea. If they get into the blood, the allergens can cause hives or more serious reactions. Hives are red, itchy blotches on the skin. Food allergens can also cause anaphylaxis (pronounced a-nehfeh-LAK-siss). Anaphylaxis (or anaphylactic shock) is a life-threatening condition in which tissues swell up and begin to close the throat. A person may go into convulsion or a coma.
  • Allergens that come into contact with the skin can cause reddening, itching, and blistering. This condition is called contact dermatitis (pronounced der-muh-TIE-tis). Skin reactions can also occur when allergens enter the body through other routes, such as the mouth or nose.
  • Allergens can enter the body through bites and stings or drug administration (injections or shots). In such cases, the allergens go directly into the bloodstream. They are then carried to other parts of the body where they can exert their effects.

People with allergies are not equally sensitive to all allergens. A person may be allergic to some kinds of food but not affected by breathing in dust or pollen. Sensitivity to allergens can also change over time. A person may become more (or less) allergic to certain allergens as he or she grows older.

Allergy flow chart. (Illustration by Hans & Cassidy)
Allergy flow chart. (Illustration by
Hans & Cassidy
)

CAUSES

When allergens enter the body, they set off a series of reactions. The first of these reactions occurs when the allergens come into contact with lymphocytes (pronounced LIM-fuh-sites), a type of white blood cells. Lymphocytes produce a special kind of marker molecule known as immunoglobulin (pronounced IM-yuh-no-GLOB-yuh-lin) type E (IgE). IgE molecules search out and attach themselves to a second kind of cell, called mast cells.

Mast cells manufacture a chemical known as histamine (pronounced HISS-tuh-meen). When IgE molecules attach themselves to a mast cell, the cell begins to release large amounts of histamine into blood vessels, nerves, and other tissue around it. Histamine causes changes in the cells with which it comes into contact. For example, it causes blood vessels to become leaky. Fluid escapes from the blood vessel, causing swelling and redness in surrounding tissue.

Histamine also causes nerve cells to become more sensitive, producing pain and irritation. All of these changes result in the familiar symptoms of an allergic reaction: redness, swelling, pain, and itching.

Common Allergens

The most common allergens in the air are:

  • Animal fur and dander (dry skin that is shed)
  • Cigarette smoke
  • Dust
  • House mites
  • Mold spores (seeds)
  • Plant pollen
  • Solvents (chemicals used in cleaning)

Common food allergens include:

  • Eggs
  • Fish and shellfish
  • Food additives
  • Milk
  • Nuts, especially peanuts, walnuts, and Brazil nuts
  • Wheat

CAN YOU INHERIT ALLERGIES?

Specific kinds of allergies are not inherited. But the tendency to develop some kinds of allergies can be. This pattern is thought to result from the body's tendency to produce IgE. The more IgE the body produces, the more likely a person is to have allergies. IgE is a hereditary trait. Some people's bodies naturally produce more or less of the chemical, a trait they can pass on to their children.

If neither parent has allergies, the chance of a child developing an allergy is no more than 20 percent. If one parent has allergies, the chance rises to as high as 50 percent. If both parents have allergies, the chance can be as high as 75 percent.

The following types of drugs often cause allergic reactions:

  • Flu vaccines
  • Gamma globulin (pronounced GA-muh GLAH-byu-lun), which are used to treat infectious diseases such as measles (see measles entry) and hepatitis (see hepatitis entry)
  • Penicillin and other antibiotics Common causes of contact dermatitis include the following:
  • Latex products (such as rubber gloves)
  • Nickel or nickel alloys
  • Poison ivy, poison oak, and poison sumac

Insects or other animals whose bites or stings can cause allergies include the following:

  • Bees, wasps, hornets, and yellow jackets
  • Fleas
  • Mosquitoes

SYMPTOMS

Symptoms depend on the specific kind of allergic reaction. Allergens in the air can cause an itchy, runny nose with post-nasal drip. Post-nasal drip occurs when fluid runs out of the back of the nose into the throat. When this happens, the throat can become scratchy and irritated. The thin membrane around the eye can also become irritated by allergens in the air. When this happens, the eye becomes red and itchy and begins to produce tears. Severe reaction to allergies may cause a disease called asthma. The symptoms of asthma include wheezing, coughing, and shortness of breath.

Food allergens can cause a variety of symptoms depending on a person's sensitivity to the allergen and the part of the body to which it goes. In the mouth and throat, an allergen can cause swelling and tingling in the lips, tongue, or throat. In the stomach, it can cause nausea, cramps, and diarrhea.

Contact dermatitis is marked by red, itchy skin that may develop skin blisters that ooze fluid.

Allergic reactions that spread throughout the body can occur with any kind of allergen. They tend to be more common, however, with allergens that enter the bloodstream through an insect bite or injection. Anaphylaxis is one of the most dangerous of these reactions.

DIAGNOSIS

Diagnosis of allergies usually occurs in two steps. First, a doctor takes a medical history of the patient. He or she tries to find some connection between an allergic reaction and a particular allergen, such as a specific food or insect bite.

Second, direct tests can be carried out to discover the allergens to which a patient might be sensitive. In skin patch tests, for example, small amounts of many different allergens are placed directly on a person's skin. Any reaction that occurs to an allergen indicates that the person is allergic to that allergen.

TREATMENT

A large number of prescription and over-the-counter drugs are available for treating allergic reactions. Most of these work by interfering with the action of histamine on cells. Other drugs counteract the effects of histamine. They stimulate other systems or reduce immune responses in general.

Antihistamines

Antihistamines prevent histamine from exerting its effect on nasal (nose) cells. They can be used after an allergic reaction has begun. But they are more effective if used preventively, before symptoms appear. Many people take an antihistamine every day, whether they feel uncomfortable or not.

A wide variety of antihistamines is available. They are among the most widely sold of all drugs. Older types of antihistamines often caused drowsiness as a side effect. Included among these drugs are diphenhydramine (pronounced DIE-fen-HI-druh-meen, trade name Benadryl), chlorpheniramine (pronounced KLOR-fen-er-uh-meen, trade name Chlor-trimeton), brompheniramine (pronounced BROM-fen-er-uh-meen, trade name Dimetane), and clemastine (pronounced KLEM-uh-steen, trade name Tavist).

Newer antihistamines do not cause drowsiness. They are available by prescription and include drugs such as astemizole (pronounced a-STEM-uh-zole, trade name Hismanal), loratadine (luh-RAT-uh-deen, trade name Claritin), and fexofenadine (pronounced fex-o-FEN-uh-deen, trade name Allegra). One of the most popular antihistamines was terfenadine (pronounced tir-FEN-uh-deen, trade name Seldane), the original nondrowsiness medication. It was taken off the market by its manufacturers in 1998 because questions about its safety had arisen. In addition, a safer alternative, fexofenadine, had become available.

Allergy scratch test. (Reproduced by permission of Custom Medical Stock Photo)
Allergy scratch test. (Reproduced by permission of
Custom Medical Stock Photo
)

Decongestants

Decongestants have the opposite reaction on blood vessels from that of histamines. They cause the blood vessels to constrict and hold fluid better. Therefore, they reduce the swelling, itchiness, and redness usually caused by histamine.

Decongestants can be taken in the form of nasal sprays or pills. They should be used with caution as they can produce side effects such as headaches, increased blood pressure and heart rate, and agitation. If used for too long a period of time, they can also cause a rebound effect. In a rebound effect, the nasal passages become even more swollen and tender than they were originally.

Topical Corticosteroids

Topical corticosteroids (pronounced KOR-ti-ko-steer-oids) are drugs used directly on the skin that reduce inflammation of mucous membranes, the tissues that line the nose, mouth, and other body openings. Topical corticosteroids tend to work more slowly and last longer than other allergy medications. A person generally starts to apply these drugs before an allergic reaction (such as hay fever) begins. The drugs can provide an extended period of protection, throughout the period during which the allergen is present.

Mast Cell Stabilizers

Mast cell stabilizers prevent mast cells from releasing histamine, which means they prevent the symptoms of allergies from developing. The most common mast cell stabilizer is cromolyn (pronounced KRO-muh-lun) sodium. The drug is often taken year-round in the form of a nose or throat spray.

Immunotherapy

Immunotherapy is also known as desensitization. This treatment takes the form of a series of injections (shots) taken over long periods of times (months or years). The shots contain a chemical that reduces the ability of IgE to cause allergic reactions. The amount of this chemical in the injection is gradually increased over time.

The effects of immunotherapy often do not show up for long periods of time. With about 20 percent of all patients, they are never very effective. The most serious possible side effect of a desensitization injection is anaphylactic shock.

Bronchodilators

Allergic reactions in the lungs cause airways to tighten, which makes it difficult for a person to breathe. Bronchodilators (pronounced brong-ko-die-LATE-urs) are substances that reverse this action. They cause air passages to dilate, or become more open, so that air flows more easily through them.

Bronchodilators are commonly used in serious asthma attacks. They are administered through nose or throat sprays. In the most serious cases, these drugs can be injected directly into the bloodstream. Some commonly used bronchodilators are adrenaline (pronounced uh-DREN-uh-lin), albuterol (pronounced al-BYOO-tuh-rol), various steroids, and theophylline (pronounced thee-OFF-uh-lin), a component of coffee and tea.

Treatment of Contact Dermatitis

Calamine lotion and corticosteroid creams can reduce the discomfort and itching of contact dermatitis. Overuse of corticosteroids can, however, lead to dry and scaly skin.

Treatment of Anaphylaxis

Anaphylaxis is one of the most serious conditions relating to allergic reactions. A person who goes into anaphylactic shock must be treated very quickly or he or she may die. The standard treatment for anaphylaxis is an injection of adrenalin, also known as epinephrine (pronounced EP-uh-nefrin). People who are at risk for anaphylaxis often carry with them an Epipen, a small needle containing a dose of adrenalin.

Alternative Treatment

The most effective alternative to medical treatment for allergies is to avoid the allergens that cause them. A person who is allergic to peanuts, for example, should avoid eating peanuts or foods that contain them.

In addition, a number of natural products have been found to be effective in treating allergic reactions. Products that have been suggested as alternatives for each of the medical treatments that have been discussed include:

  • Antihistamines: Vitamin C and the natural product known as hesperidin (pronounced he-SPER-i-din).
  • Decongestants: Vitamin C, the amino acid N-acetylcysteine (pronounced uh-seet-uhl-SIS-tuh-een), and the minerals iron phosphate and potassium chloride.
  • Mast cell stabilizers: The natural products hesperidin and quercetin (pronounced KWER-si-tin).
  • Immunotherapy: The herbs echinacea (ek-i-NAY-see-uh) and milk-vetch root (astragalus, pronounced uh-STRAG-uh-luhs).
  • Bronchodilators: The herbs ephedra (pronounced i-FED-ruh), khellin (pronounced KEL-un), and cramp bark.

Alternative Treatment of Contact Dermatitis

The use of certain herbs taken internally or applied directly to the skin has been recommended as a treatment for the pain and itching of contact dermatitis. One treatment consists of a paste containing jewelweed or chickweed applied to the skin. A cream containing calendula (pronounced KUH-len-juh-luh) sometimes relieves a rash. The use of certain drinks or pills made of herbs may also be effective against contact dermatitis.

PROGNOSIS

Some allergies become less severe over time, while others become more serious. Anaphylaxis and asthma are the most serious problems associated with allergies. Either can result in death if not properly treated.

PREVENTION

The best approach for dealing with allergies is to find out which allergens cause sensitivity and then avoid them to the greatest extent possible. If one is allergic to certain foods, for example, those foods must be avoided. Allergens carried through the air can be the most difficult to avoid. The best approach is to keep a house as clean as possible, to avoid animals that cause allergic reactions, and to be aware of other housekeeping activities that will reduce the number of allergens to which one is exposed.

See also: Hay fever.

FOR MORE INFORMATION

Books

Novick, N. L. You Can Do Something about Your Allergies. New York: Macmillan, 1994.

Weil, A. Natural Health, Natural Medicine: A Comprehensive Manual for Wellness and Self-Care. Boston: Houghton Mifflin, 1995.

Organizations

American Academy of Allergy, Asthma, and Immunology. (800) 822–2762. http://www.aaaai.org.

National Institute of Allergy and Infectious Diseases. Building 31, Room 7A-50, 31 Center Drive, MSC 2520, Bethesda, MD 20892–2520. http://www.niaid.nih.gov.

Web sites

The On-Line Allergy Center. [Online] http://www.onlineallergycenter.com (accessed on October 5, 1999).