Allergy

Allergies are inappropriate or exaggerated reactions of the immune system to substances that, in the majority of people, cause no symptoms. Symptoms of the allergic diseases may be caused by different exposures such as a certain chemical affecting the skin, dust or pollen particles affecting the respiratory system, or particular foods affecting the stomach and intestines.

Anaphylaxis

Anaphylaxis, or anaphylactic shock, is a severe, frightening and life-threatening allergic reaction. The reaction, although rare, can occur after an insect sting or as a reaction to an injected drug -- for example, penicillin or antitetanus (horse) serum. Less commonly, the reaction occurs after a particular food or drug has been taken by mouth.

Antibody

An antibody is a protein (also called an immunoglobulin) that is manufactured by types of white blood cell to neutralize an antigen or foreign protein. Bacteria, viruses, and other microorganisms commonly contain many antigens, as do pollens, dust mites, molds, foods and other substances. Although many types of antibodies are protective, inappropriate or excessive formation of certain types of antibodies may lead to illness. When the body forms a type of antibody called IgE (immunoglobulin E), allergic rhinitis, asthma or eczema may result when the patient is again exposed to the substance (whereby an antigen is then termed an allergen) that caused IgE antibody formation.

Antigen

An antigen is a substance that can trigger an immune response, resulting in production of an antibody as part of the body's defense against infection and disease. Many antigens are foreign proteins (those not found naturally in the body). An allergen is a special type of antigen that causes an IgE antibody response.

Antihistamine drugs

Antihistamines are a group of drugs that block the effects of histamine, a chemical released in body fluids during an allergic reaction. In rhinitis, antihistamines reduce itching, sneezing and runny nose.

Anti-inflammatory drugs

Anti-inflammatory drugs reduce the symptoms and signs of inflammation. Examples include aspirin, ibuprofen and corticosteroids.

Asthma

Asthma is a chronic, inflammatory lung disease characterized by recurrent breathing problems. People with asthma have acute episodes when the air passages in their lungs get narrower, and breathing becomes more difficult. Sometimes episodes of asthma are triggered by allergens, although infection, exercise, cold air and other factors are also important triggers.

Bronchodilator drugs

Bronchodilators are a group of drugs that reduce spasms in the airways in the lungs.

Bronchus

A bronchus is any of the larger air passages that connect the trachea (windpipe) to the lungs. The plural form of "bronchus" is "bronchi."

Chronic bronchitis

Bronchitis is an inflammation of the bronchi (lung airways), resulting in persistent cough that produces considerable quantities of sputum (phlegm). Bronchitis is more common in smokers and in areas with high atmospheric pollution.

Contact dermatitis

Contact dermatitis is an inflammation of the skin, or a rash caused by contact with various substances of a chemical, animal or vegetable nature. The reaction may be an immunologic response or a direct toxic effect of the substance. Among the more common causes of a contact dermatitis reaction are detergents left on washed clothes, nickel (in watch straps, bracelets, necklaces and the fastenings on underclothes), chemicals in rubber gloves and condoms, certain cosmetics, plants such as poison ivy, and topical medications.

Corticosteroid drugs

Corticosteroids are a group of potent anti-inflammatory drugs similar to the natural corticosteroid hormones produced by the cortex of the adrenal glands. Among the disorders that often improve with corticosteroid treatment are asthma, allergic rhinitis, eczema and rheumatoid arthritis.

Digestive system

The digestive system is the group of organs that breaks down food into chemical components that the body can absorb and use for energy, and for building and repairing cells and tissues.

Eczema

This condition is an inflammation of the skin, usually causing itching and sometimes accompanied by crusting, scaling, or blisters. A type of eczema often made worse by allergen exposure is termed "atopic dermatitis."

Epinephrine

Epinephrine is a naturally occurring hormone, also called adrenaline. It is one of two chemicals (the other is norepinephrine) released by the adrenal gland. Epinephrine increases the speed and force of heartbeats and, thereby, the work that can be done by the heart. It dilates the airways to improve breathing and narrows blood vessels in the skin and intestine so that an increased flow of blood reaches the muscles and allows them to cope with the demands of exercise. Epinephrine has been produced synthetically as a drug since 1900. It remains the drug of choice for treatment of anaphylaxis.

Extrinsic asthma

Extrinsic asthma is asthma that is triggered by an allergic reaction, usually something that is inhaled.

Hay fever

See Rhinitis.

Histamine

Histamine is a chemical present in many cells throughout the body that is released during an allergic reaction. It is one of the substances responsible for the symptoms of inflammation and is the major reason for running of the nose, sneezing and itching in allergic rhinitis. It also stimulates production of acid by the stomach and narrows the bronchi or airways in the lungs.

Hives

See Urticaria.

Immune system

The immune system is a collection of cells and proteins that works to protect the body from potentially harmful, infectious microorganisms, such as bacteria, viruses and fungi. The immune system plays a role in the control of cancer and other diseases but also is the culprit in the phenomena of allergies, hypersensitivity, and the rejection of transplanted organs, tissues, and medical implants.

Immunoglobulins

Immunoglobulins, also known as antibodies, are proteins found in blood and in tissue fluids. Immunoglobulins are produced by cells of the immune system called B-lymphocytes. Their function is to bind to substances in the body that are recognized as foreign antigens (often proteins on the surface of bacteria and viruses). This binding is a crucial event in the destruction of the microorganisms that bear the antigens. Immunoglobulins also play a central role in allergies when they bind to antigens that are not necessarily a threat to health and provoke an inflammatory reaction.

Immunotherapy

Immunotherapy ("allergy shots") is a form of preventive treatment of allergy to substances such as pollens, house dust mites, fungi, and stinging insect venom. Immunotherapy involves giving gradually increasing doses of the substance, or allergen, to which the person is allergic. The incremental increases of the allergen cause the immune system to become less sensitive to the substance, perhaps by causing production of a particular "blocking" antibody, which reduces the symptoms of allergy when the substance is encountered in the future.

Inflammation

Inflammation is the redness, swelling, heat and pain in a tissue due to chemical or physical injury, or to infection. It is a characteristic of allergic reactions in the nose, lungs and skin.

Intrinsic asthma

Intrinsic asthma is asthma that has no apparent external cause. This type of asthma is directly caused by other environmental agents, such as perfumes, vapors or even viral infections that directly stimulates the nervous system and triggers an inflammatory response.

Lymphocyte

A lymphocyte is any of a group of white blood cells of crucial importance to the adaptive part of the body's immune system. The adaptive portion of the immune system mounts a tailor-made defense when dangerous invading organisms penetrate the body's general defenses.

Mast cell

Mast cells play an important role in the body's allergic response. Mast cells are present in most body tissues but are particularly numerous in connective tissue, such as the dermis (innermost layer) of skin. In an allergic response, an allergen stimulates the release of antibodies, which attach themselves to mast cells. Following subsequent allergen exposure, the mast cells release substances such as histamine (a chemical responsible for allergic symptoms) into the tissue.

RAST

RAST is an abbreviation for radioallergosorbent test, a trademark of Pharmacia Diagnostics, which originated the test. RAST is a laboratory test used to detect IgE antibodies to specific allergens.

Respiratory system

The respiratory system (including the sinuses, nasal passages and lungs) is responsible for processing the air we breathe and then carrying oxygen from the air to the bloodstream and for expelling the waste product carbon dioxide.

Rhinitis

Rhinitis is an inflammation of the mucous membrane that lines the nose, often due to an allergy to pollen, dust or other airborne substances. Seasonal allergic rhinitis is also known as "hay fever," a disorder that causes sneezing, itching, a runny nose and nasal congestion.

Sinus

The sinuses (paranasal sinuses) are air cavities within the facial bones. They are lined by mucous membranes similar to those in other parts of the airways.

Sinusitis

Sinusitis is inflammation of the membrane lining the facial sinuses, most often caused by viral infections or allergies. Occasionally bacterial infection occurs after no less than seven days of symptoms.

Theophylline

Theophylline is a bronchodilator drug, given by mouth that widens the airways to the lung. It also is used to prevent attacks of apnea (cessation of breathing) in premature infants, and to treat heart failure because it stimulates heart rate and increases urine excretion.

Urticaria

Urticaria is a skin condition commonly known as hives, characterized by the development of itchy, raised white lumps surrounded by an area of red inflammation.

Related Articles Basic Information About Allergies Common Allergies Allergy Diagnosis

External Source American College of Allergy, Asthma & Immunology

This article was reviewed and updated June 2007.