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Allergies are abnormal reactions to ordinarily harmless substances. These sensitizing substances, called allergens, may be inhaled, swallowed, or come into contact with the skin.

Allergens that most frequently cause problems are: pollens, mold spores, house dust mites, animal danders, foods, insect bites, medications and environmental conditions (such as cold temperatures).

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Normally, the body learns to defend itself through experience - by encountering, battling and remembering one enemy after another. For decades, medical science has taken advantage of this ability by using vaccination to create immunity - the immunologic "memory" of a disease. Allergic reactions occur after the immune system mistakenly learns to recognize innocent foreign substances (allergens) as potentially harmful.

The following story illustrates how an allergy can develop:

    Over a field of ragweed plants floats an invisible cloud of pollen grains, soon carried by the wind into a nearby town. The pollen is inhaled by a child whose body has never been exposed to this substance before.

    Because of some defect or genetic predisposing factor, this child's immune system overreacts and produces large numbers of IgE antibodies, all specially designed to respond to ragweed pollen. Several of the antibodies attach themselves to cells in the child's nasal passages and upper respiratory tract.

    These cells (known as mast cells) contain strong chemicals called mediators, the best-known of which is histamine.

    Later, when the child inhales the same kind of pollen again, proteins from the pollen bind in a lock-and-key fashion to the specially designed antibodies on the surface of the mast cells. This sets off an explosion of sorts, as the mediators burst from inside the mast cells, destroying the pollen and also damaging surrounding tissues. The results are sneezing, sniffling, stuffed-up head and red, watery eyes - well-known hallmarks of allergies.

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Causes and Risk Factors

The fundamental cause of allergy is still not known. The problem has a tendency to run in families. An allergic individual is more likely to have relatives who are allergic than would be expected on the basis of chance, but non-hereditary factors apparently play a part as well. Evidence of this is the fact that infants who are breast-fed are less likely to develop allergies than bottle-fed babies.

The reason an individual becomes sensitive to some substances and not to others remains a mystery.

Individuals can be affected by a variety of allergic diseases. The most common allergic diseases are allergic rhinitis, non-allergic rhinitis, asthma, allergic dermatitis, contact dermatitis and urticaria. (Allergic rhinitis is the most common of the allergic diseases and the main focus of this health profile. More comprehensive information about the other conditions may be found under that particular term.)

Allergic rhinitis is a general term used to apply to anyone who has allergy-based symptoms. Allergic rhinitis can be a seasonal problem (commonly known as "hay fever" or pollen allergy) or a year-round problem (commonly known as perennial allergic rhinitis). Hay fever or seasonal allergic rhinitis is caused by allergy to pollens of trees, grasses, weeds or mold spores. Perennial allergic rhinitis is caused by house dust, animal danders, mold and some foods.

Non-allergic rhinitis is caused by medications, environmental factors such as fumes, odors and temperature, or it can be associated with polyps or structural abnormalities.

Asthma is caused by intrinsic and extrinsic (inhaled) factors. Intrinsic factors are pollens, dust, dust mites, animal fur, animal dander or feathers. Extrinsic factors are respiratory infections; a cough, cold or bronchitis; exercise and tobacco smoke or other air pollutants, and can be caused by an allergy to a particular food or medication (refer to the Health Profile on Asthma for more information).

Allergic dermatitis, also known as "eczema", can be caused by foods or another allergens (refer to the Health Profile on Eczema for more information).

Contact dermatitis is caused by exposure to certain plants (such as poison ivy), cosmetics, medications, metals and chemicals.

Urticaria, also known as "hives", is caused by allergy to foods, such as nuts, tomatoes, shellfish and berries. Hives can also be caused by medications, such as aspirin and penicillin.

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The signs and symptoms of allergic rhinitis and non-allergic rhinitis are:

  • sneezing, often accompanied by a runny or clogged nose

  • coughing and postnasal drip

  • itching eyes, nose and throat

  • allergic shiners (dark circles under the eyes caused by increased blood flow near the sinuses)

  • the "allergic salute" (in a child, persistent upward rubbing of the nose that causes a crease mark on the nose)

  • watery eyes

  • conjunctivitis (an inflammation of the membrane that lines the eyelids, causing red-rimmed, swollen eyes and crusting of the eyelids)

The signs and symptoms of asthma are:

  • a feeling of tightness in the chest

  • breathlessness

  • coughing

  • difficulty inhaling and exhaling

  • noisy breathing ("wheezing")

The signs and symptoms of allergic dermatitis, contact dermatitis and urticaria are:

  • red, itchy skin

  • inflamed skin

  • welts (in hives)

Warning: If a person is experiencing more severe symptoms than what is tin this list, they may be in anaphylactic shock.

Anaphylactic shock is a medical emergency which is an acute systemic (affecting the whole body) allergic reaction. It occurs after exposure to an antigen (allergen) to which a person was previously sensitized.

The signs and symptoms of anaphylactic shock include the general symptoms of a common allergic reaction, PLUS:

  • anxiety

  • itching of the skin

  • headache

  • nausea and vomiting

  • abdominal cramps

  • swelling of tissues such as lips or joints

  • diarrhea

  • shortness of breath and wheezing

  • low blood pressure

  • convulsions

  • loss of consciousness

  • itching of the mouth and throat

  • hoarseness

  • change of voice

  • chest pain and tightness

  • a feeling of warmth and flushing

  • redness of the skin

  • cramping of the uterus

  • the feeling of having to urinate

Allergens more commonly associated with anaphylactic shock are: certain insect venoms; drugs such as penicillin; and foods like fish, peanuts, nuts, eggs and seeds.

If not treated promptly and properly, anaphylaxis can result in death. Fortunately, the tendency to have such serious reactions is rare.

For treatment of anaphylactic shock, the first step is to inject adrenaline (epinephrine) to constrict the small blood vessels, raise blood pressure and dilate the airway. This may be followed by injection of antihistamines and/or steroids, plus the use of life-support systems.

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Besides a thorough medical history, the doctor will perform a number of skin tests and/or a blood test called radioallergosorbent test (RAST).

There are three skin tests used to evaluate and diagnose allergies, the prick method, the intradermal test and the patch test:

  • The prick method is the most common type of skin test. This test is done by placing a drop of allergen extract on the skin on the back and passing a needle through the extract and making a tiny puncture in the skin. If allergic to the allergen a hive will appear at the site of the puncture within about 15 minutes. The doctor can perform multiple prick tests with varying allergen extracts simultaneously.

  • The intradermal test uses a syringe to inject the allergen extract into the top layer of skin in the upper arm, which raises a small bubble on the skin surface. Like the prick method, a hive will appear indicating an allergic reaction.

  • The patch test can be used to look for substances that might be causing contact dermatitis. A suspected allergen is placed on the skin and covered with a bandage for 48 hours. If the patient is allergic, the skin will become red and peel.

When skin testing is not feasible, as in the case of people with eczema and other skin conditions, RAST is used. Diagnostic tests can be done by using a blood sample from a patient to detect the levels of IgE antibody to a particular allergen.

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There are three general approaches to the treatment of allergic diseases such as allergic rhinitis and non-allergic rhinitis: avoidance of the allergen, medication to relieve symptoms and allergy shots.


  • Wear a pollen mask when mowing the grass or housecleaning.

  • Stay indoors in the morning (when the pollen count is at its highest) and on windy days.

  • Read and understand food labels (for people with food allergies).

  • Keep windows and doors closed during heavy pollination seasons.

  • Use the air conditioner in the house and car.

  • Rid the home of indoor plants and other sources of mildew.

  • Don't allow dander-producing animals in the house.

  • Change feather pillows, woolen blankets and clothing to cotton or synthetic materials.

  • Enclose mattress, box springs and pillows in plastic barrier cloth.

  • Wash sheets, mattress pad and blankets weekly in hot water (at least 130F).

  • Remove carpets and upholstered furniture (drastic measure).

  • Use acaricide (a chemical that kills house-dust mites) or a tannic acid solution (solution that neutralizes the allergen in mite droppings).

  • Use air filters.

  • Use a dehumidifier.


When avoidance or control of an allergen isn't possible, medications may be necessary. The general allergy medications prescribed are:

  • Decongestants: administered via spray or orally to unclog nasal passages. Spray decongestants include Afrin, 4-Way and Vicks Sinex.

    Oral decongestants include Sinutab, Sudafed and Tylenol Sinus.

  • Steroid nasal sprays: administered via spray to mute the inflammatory response.

    Medications include Beconase, Flonase and Vancenase.

  • Antihistamines: drugs that block the action of histamine, which is responsible for allergic symptoms.

    Prescription antihistamines include Hismanal, Allergra, Zyrtec and Claritin. Nonprescription antihistamines include Benadryl, Chlor-Trimeton and Tavist. New to the market, and available by prescription only, is an antihistamine nasal spray called Astelin.

  • Cromoglycate (or related agents): administered mostly as eyedrops or nasal sprays to help prevent attacks. In January 1997 the Food and Drug Administration (FDA) approved the sale of Nasalcrom (a nasal spray containing cromolyn sodium) as an over-the-counter (OTC) product.


When avoidance, environmental control measures and medications fail to control allergy symptoms, the doctor may suggest immunotherapy ("allergy shots"). Immunotherapy involves the injections of allergen extracts to "desensitize" the person.

Typically, the treatment begins with injections of a weal solution of allergen given one to five times a week, with the strength gradually increasing. When the maximum dose is reached, maintenance injections are given at increasing intervals until the patient receives injections only once a month.

It may take up to six months or so to show results. It usually takes about three to four years for the patient to be free of symptoms.

Treatment of Asthma

With all asthmatics the treatment involves agents that relax the airways. These agents include beta-adrenergic agonists, theophylline, anti-cholinergics and occasionally expectorants and mucolytics.

Treatment of Allergic Dermatitis, Contact Dermatitis and Urticaria

Eczema (allergic dermatitis) and contact dermatitis can be treated with corticosteroid creams or ointments (topical steroids). Hives (urticaria) can be relieved by applying calamine lotion or by taking antihistamine drugs. More severe cases of hives may require corticosteroid drugs.

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Questions to Ask Your Doctor

Should skin testing be done?

Do you recommend nasal sprays or drops? What are the side effects?

What other medications are recommended to relieve the symptoms of allergies?

Do you recommend desensitization with injections?

What measures can be taken minimize the reactions?

Do allergic rhinitis (hayfever) reactions lead to sinus infections or asthma or any other condition?

Are foods causing the allergies?

Am I at risk for anaphylactic shock? If so, what precautions can I take?

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