Sneezing is not always
the symptom of a cold. Sometimes, it is an allergic reaction to something in
the air. According to the American Academy of Allergy, Asthma, and Immunology,
40 million Americans suffer from upper respiratory symptoms that are allergic
reactions to airborne pollen. Pollen allergy, commonly called hay fever, is
one of the most common chronic diseases in the United States. Worldwide, airborne
dust causes the most problems for people with allergies. The respiratory symptoms
of asthma, which affect more than 15 million Americans, are often provoked
by airborne allergens (substances that cause an allergic reaction).
Overall, allergic diseases are among the major causes of illness and disability
in the United States, affecting more than 50 million Americans. The National
Institute of Allergy and Infectious Diseases, a component of the National Institutes
of Health, conducts and supports research on allergic diseases. The goals of
this research are to provide a better understanding of the causes of allergy,
to improve the methods for diagnosing and treating allergic reactions, and
eventually to prevent allergies.
Why are some people allergic to
these substances while others are not?
Scientists think that people inherit a tendency to be allergic, meaning an
increased likelihood of being allergic to one or more allergens, although they
probably do not have an inherited tendency to be allergic to any specific allergens.
Children are much more likely to develop allergies if their parents have allergies,
even if only one parent is allergic. Exposure to allergens at certain times
when the body's defenses are lowered or weakened, such as after a viral infection
or during pregnancy, seems to contribute to the development of allergies.
Symptoms of allergies to airborne
The signs and symptoms are familiar to many:
- 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)
- Watering eyes
- Conjunctivitis (an inflammation of the membrane that lines the eyelids,
causing red-rimmed, swollen eyes, and crusting of the eyelids)
In people who are not allergic, the mucus in the nasal passages simply moves
foreign particles to the throat, where they are swallowed or coughed out. But
something different happens to a person who is sensitive to airborne allergens.
As soon as the allergen lands on the mucous membranes lining the inside of
the nose, a chain reaction occurs that leads the mast cells in these tissues
to release histamine and other chemicals. These powerful chemicals contact
certain cells that line some small blood vessels in the nose. This allows fluids
to escape, which causes the nasal passages to swell, resulting in nasal congestion.
Created by National Institute of Allergy and Infectious Diseases
American Academy of Allergy, Asthma & Immunology (AAAAI). The Allergy
Report: Science Based Findings on the Diagnosis & Treatment of Allergic
Disorders, 1996-2001. Milwaukee, Wis: American Academy of Allergy, Asthma & Immunology
(AAAAI); 2001. (2007 updated version available online at www.theallergyreport.com.)
Review Date: 5/16/2007
Reviewed By: Alan Greene, M.D., F.A.A.P., Department of Pediatrics, Packard Children's Hospital, Stanford University School of Medicine; Chief Medical Officer, A.D.A.M., Inc.
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