Glossary: Allergies

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Glossary

allergen: A harmless substance that triggers the immune system to mount an inappropriate response known as an allergic reaction.

allergic: Having an overly sensitive immune response to one or more harmless substances. 

allergy: The mounting of inappropriate immune responses to one or more harmless substances. The result is the onset of an excessive inflammatory reaction.

anaphylaxis: A severe, potentially life-threatening systemic allergic reaction. Also called anaphylactic shock.

antibodies: Molecules produced by plasma cells, the descendants of B cells. When foreign molecules enter the body, antibodies swiftly travel to potential trouble spots where they use various strategies to stop the spread of infection.

antigen: A foreign (nonself) molecule that causes an immune response.

antihistamines: Drugs that block the action of histamine, thereby dampening the ferocity of an immediate allergic reaction.

antileukotrienes: Drugs that block the action of leukotrienes. Used in the treatment of asthma and allergic rhinitis. Also known as leukotriene modifiers.

asthma: A chronic inflammatory disease of the airways that typically starts in childhood, although some people develop asthma later in life.

atopic: Having an inherited predisposition to allergies. The term is often used interchangeably with “allergic,” although not all allergies have a genetic component.

atopic dermatitis (eczema): A chronic inflammatory skin condition that usually initially appears in young children who have an inherited predisposition to allergies. Many children with atopic dermatitis go on to develop atopic (allergic) rhinitis or atopic (allergic) asthma.

atopic rhinitis: A seasonal or year-round allergic condition marked by sneezing, runny nose, and congestion. The most common type of allergy, it is caused by an IgE-mediated immune response.

atopy: The inherited tendency to develop allergies. The three major atopic diseases are atopic rhinitis, atopic asthma, and atopic dermatitis.

B cell: A type of lymphocyte (white blood cell). B cells, together with T cells, are the “big guns” of the immune system response to an invasion by a foreign molecule.

challenge testing: A method of testing for food allergy, usually in double-blind experiments in which neither patient nor doctor knows which food is taken in a pharmaceutically prepared pill.

conjunctivitis: Inflammation of the conjunctiva of the eye. Conjunctivitis is the most common eye allergy.

contact dermatitis: A reaction that occurs when the skin comes in direct contact with an allergen or an irritant.

corticosteroids (steroids): Medications with anti-inflammatory properties commonly used to treat a range of allergies.

decongestants: Medications used to relieve the stuffy-nose symptoms of IgE-mediated allergies. Decongestants should be used judiciously; overuse exacerbates the problem.

eczema: See atopic dermatitis.

elimination diets: A way of diagnosing food allergies in which suspected foods are eliminated from the diet one at a time to see if the allergic condition improves. Also called avoidance diets.

eosinophils: White blood cells that play an important role in allergic reactions.

EpiPen: A device to administer epinephrine very quickly to stave off anaphylaxis in the event of a severe allergic reaction.

food allergies: Conditions that result from the immune system’s response to certain proteins found in foods.

hay fever (seasonal rhinitis): Seasonal allergies to common inhaled allergens.

helper T cells: A subset of T cells. Th2 cells favor the inappropriate immune response seen in allergic reactions.

HEPA filter: High-efficiency particulate air filter, found in vacuums or in stand-alone devices.

histamine: A substance released by mast cells that causes symptoms of an immediate allergic reaction.

hygiene hypothesis: A suggested explanation for the increase in allergies in industrialized countries. The hypothesis proposes that modern-day cleanliness results in less early exposure to germs and this upsets the balance of the immune response to allergens.

immunoglobulin E (IgE): The antibody responsible for the majority of allergic reactions. Triggered by allergens, IgE on the surface of mast cells fires up the explosive release of histamine.

immunotherapy (allergy shots): A long-term program of desensitization that induces tolerance to an identified allergen. This treatment is commonly used for allergic rhinitis, asthma, allergies to stinging insects, and conjunctivitis.

intolerance: A reaction that has similar symptoms to an allergic reaction but does not engage the immune system and so is not an allergy.

irritants: Substances (tobacco or wood smoke, perfumes, and so on) that cause allergy-like symptoms, although the response is not an allergic reaction.

latex allergy: An allergic reaction to the proteins found in natural rubber.

leukotrienes: Chemicals responsible for inflammation of the airways in diseases such as asthma.

mast cell: A type of large cell abundant in the mucosa, skin, the lining of the gut, and the airways. Mast cells play a key role in allergic reactions by releasing histamine, leukotrienes, and other inflammatory mediators.

patch test: A skin test used to diagnose contact dermatitis.

peak flow meter: A device to assess lung function, commonly used to diagnose and monitor asthma.

plasma cells: Descendants of B cells responsible for producing antibodies.

prick test: A commonly used skin test to confirm hypersensitivity to a broad range of allergens that elicit an IgE-mediated response.

RAST (radioallergosorbent test): A blood test used for identifying allergens.

spirometer: A device that measures airway obstruction, used to diagnose asthma and determine the severity of the condition.

T cell: A type of lymphocyte (white blood cell). Helper T cells play a prominent roll in the allergic response.

urticaria (hives): An itchy rash of usually short duration.

Last updated:	August 21, 2006
Reviewed By:	Faculty of Harvard Medical School