A - Z Encyclopedia

Understanding Allergies

the Basics

What Are Allergies?

The term allergy applies to an abnormal reaction by your immune system to a substance that is usually not harmful. Allergies come in a variety of forms and vary in severity from mildly bothersome to life-threatening. An estimated one-fifth of the Western Hemisphere's population suffers from allergies.

No one knows why some people develop them, but heredity seems to play a role in their development. Allergies may flare up and subside throughout your life. The immune system protects the body from foreign substances -- known as antigens -- by producing antibodies and other chemicals to fight against them. Usually the immune system ignores harmless substances, such as food, and fights only dangerous ones, such as bacteria. A person develops an allergic reaction when the immune system cannot tell the good from the bad and releases chemicals like histamine to attack the harmless substance as if it were a threat. Histamine produces many of the symptoms associated with allergies. Some of the hundreds of substances that may trigger allergic reactions range from pollen to pet dander to penicillin.

Most allergic reactions are not serious, but some, such as anaphylaxis, can result in an inability to breathe or a severe drop in blood pressure and can be fatal. Allergies can't be cured outright, but a variety of treatments are available to relieve the symptoms. If your allergy is severe, it is vital that you visit a doctor and get immediate treatment.

What Causes Them?

Allergies come in many distinct forms and are typically grouped in general categories according to the types of substances that cause them or the parts of the body they affect.

Skin allergies: Eczema - also called contact or atopic dermatitis-- is caused by direct, skin exposure to a specific allergen; atopic dermatitis has no known cause, but it is usually hereditary. Hives, or urticaria, is an eruption of itchy, swollen, reddened welts that can last for minutes or days. Angioedema is characterized by a deeper swelling around the eyes and lips, and sometimes of the hands and feet as well. Both hives and angioedema stem from the body's adverse reaction to certain foods, pollen, animal dander, drugs, insect stings, cold, heat, or light.

Respiratory allergies: Approximately 20 million Americans suffer from hay fever (allergic rhinitis). Typical symptoms include itchy eyes, nose, roof of mouth, or throat, along with nasal congestion, coughing and sneezing. If you (or members of your family) have other allergies such as dermatitis or asthma, you are more likely to have hay fever. Hay fever can be caused by a number of difference substances -- pollens of ragweed, grasses and other plants whose pollen is spread by the wind, molds, dust, and animal dander (dead skin scales and saliva). Mold allergies are caused by spores in the air. Outdoor molds thrive in warm seasons or climates, while indoor molds grow year round in damp locations (basements and bathrooms, for example). Dust causes allergies because it harbors offenders such as pollen, mold spores, and microscopic dust mites; it may also contain irritating fibers from fabrics, upholstery, and carpets.

Asthma: Asthma has various causes and factors that trigger it, including respiratory viruses, environmental exposures, and allergies to pollen, mold spores, animal dander, and dust mites.

Food allergies: True food allergies are rare in adults, but common in infants under age two. It is sometimes difficult to pinpoint the specific substances responsible for a food allergy because reactions are often delayed or may be caused by food additives or even by eating habits. However, approximately 90% of food allergies are caused by proteins in cow's milk, egg whites, peanuts, wheat, or soybeans. Other common food allergens include berries, shellfish, corn, beans, yellow food dye No. 5, and gum arabic (an additive in processed foods). The classic symptoms of food sensitivity include stomach cramps, diarrhea, and nausea. In more severe cases, there may be vomiting, swelling of the face and tongue, and respiratory congestion, as well as dizziness, sweating, and faintness.

Drug allergies: The most common drug allergy is to antibiotics in the penicillin family. Allergies have been seen to most types of antibiotics -- especially sulfa drugs. Sulfa is also found in drugs other than antibiotics, such as in the arthritis drug Celebrex. Allergies have also been seen in many other types of drugs as well, including dyes injected into blood vessels for X-rays. Almost 1 million Americans (and ten percent of people with asthma) have reactions to aspirin; these responses are not true allergies but rather "sensitivities."

Insect sting allergies: Some studies speculate that people who have other allergies (food, drug or respiratory) may be more susceptible to insect sting allergies, which affect about 15% of the population. Venom in stings of bees, wasps, hornets, yellow jackets, and fire ants is a common allergen.

What Triggers Anaphylactic Shock?

The most severe and dangerous of allergic reactions is anaphylaxis, or anaphylactic shock, which begins within minutes after exposure and advances quickly. Although any allergen can trigger anaphylactic shock, the most common are insect stings, certain foods (such as shellfish and nuts), and injections of certain drugs. Standard emergency treatment includes an injection of epinephrine to open up the airways and blood vessels; in severe cases, cardiopulmonary resuscitation (CPR) may be necessary.

Back to eHealth Encyclopedia