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General Introduction
Sneezing
is not always the symptom of a cold. Sometimes, it is an allergic
reaction to something in the air. Experts estimate that 35 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 affects approximately 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 as many as 40 to 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. This booklet summarizes what is known about the causes and
symptoms of allergic reactions to airborne allergens, how these
reactions are diagnosed and treated, and what medical researchers are
doing to help people who suffer from these allergies.
What is an allergy?
An
allergy is a specific immunologic reaction to a normally harmless
substance, one that does not bother most people. People who have
allergies often are sensitive to more than one substance. Types of
allergens that cause allergic reactions include pollens, dust
particles, mold spores, food, latex rubber, insect venom, or medicines.
Symptoms of Allergies to Airborne Substances
The signs and symptoms are familiar to many:
· Sneezing often accompanied by a runny or clogged nose
· Coughing and post nasal 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 contract 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.
Pollen Allergy
Each
spring, summer, and fall, tiny particles are released from trees,
weeds, and grasses. These particles, known as pollen, hitch rides on
currents of air. Although their mission is to fertilize parts of other
plants, many never reach their targets. Instead, they enter human noses
and throats, triggering a type of seasonal allergic rhinitis called
pollen allergy, which many people know as hay fever or rose fever
(depending on the season in which the symptoms occur). Of all the
things that can cause an allergy, pollen is one of the most widespread.
Many of the foods, drugs, or animals that cause allergies can be
avoided to a great extent; even insects and household dust are
escapable. Short of staying indoors when the pollen count is high --
and even that may not help -- there is no easy way to evade wind born
pollen.
People
with pollen allergies often develop sensitivities to other
troublemakers that are present all year, such as dust mites. For these
allergy sufferers, the "sneezin' season" has no limit. Year-round
airborne allergens cause perennial allergic rhinitis, as distinguished
from seasonal allergic rhinitis.
Click here
to find solutions to Pollen Allergies
Mold Allergy
Along
with pollens from trees, grasses, and weeds, molds are an important
cause of seasonal allergic rhinitis. People allergic to molds may have
symptoms from spring to late fall. The mold season often peaks from
July to late summer. Unlike pollens, molds may persist after the first
killing frost. Some can grow at sub-freezing temperatures, but most
become dormant. Snow cover lowers the outdoor mold count dramatically
but does not kill molds. After the spring thaw, molds thrive on the
vegetation that has been killed by the winter cold.
In
the warmest areas of the United States, however, molds thrive all year
and can cause year-round (perennial) allergic problems. In addition,
molds growing indoors can cause perennial allergic rhinitis even in the
coldest climates.
Where do molds grow?
Molds
can be found wherever there is moisture, oxygen, and a source of the
few other chemicals they need. In the fall they grow on rotting logs
and fallen leaves, especially in moist, shady areas. In gardens, they
can be found in compost piles and on certain grasses and weeds. Some
molds attach to grains such as wheat, oats, barley, and corn, making
farms, grain bins, and silos likely places to find mold.
Bakeries,
breweries, barns, dairies, and greenhouses are favorite places for
molds to grow. Loggers, mill workers, carpenters, furniture repairmen,
and upholsterers often work in moldy environments.
Click here
to find solutions to Mold
Allergies
Dust Mite Allergy
Dust
mite allergy is an allergy to a microscopic organism that lives in the
dust that is found in all dwellings and work places. Dust mites are
perhaps the most common cause of perennial allergic rhinitis. Dust mite
allergy usually produces symptoms similar to pollen allergy and also
can produce symptoms of asthma.
What is house dust?
Rather
than a single substance, so-called house dust is a varied mixture of
potentially allergenic materials. It may contain fibers from different
types of fabrics; cotton lint, feathers, and other stuffing materials;
dander from cats, dogs, and other animals; bacteria; mold and fungus
spores (especially in damp areas); food particles; bits of plants and
insects; and other allergens peculiar to an individual home.
House
dust also contains microscopic mites. These mites, which live in
bedding, upholstered furniture, and carpets, thrive in summer and die
in winter. In a warm, humid house, however, they continue to thrive
even in the coldest months. The particles seen floating in a shaft of
sunlight include dead dust mites and their waste-products. These
waste-products, which are proteins, actually provoke the allergic
reaction.
Click here to find solutions to House Dust and Dust Mite Allergies
Animal Allergy
Household
pets are the most common source of allergic reactions to animals. Many
people think that pet allergy is provoked by the fur of cats and dogs.
But researchers have found that the major allergens are proteins
secreted by oil glands in the animals' skin and shed in dander as well
as proteins in the saliva, which sticks to the fur when the animal
licks itself. Urine is also a source of allergy-causing proteins. When
the substance carrying the proteins dries, the proteins can then float
into the air. Cats may be more likely than dogs to cause allergic
reactions because they lick themselves more and may be held more and
spend more time in the house, close to humans.
Some
rodents, such as guinea pigs and gerbils, have become increasingly
popular as household pets. They, too, can cause allergic reactions in
some people, as can mice and rats. Urine is the major source of
allergens from these animals.
Allergies
to animals can take two years or more to develop and may not subside
until six months or more after ending contact with the animal. Carpet
and furniture are a reservoir for pet allergens, and the allergens can
remain in them for four to six weeks. In addition, these allergens can
stay in household air for months after the animal has been removed.
Therefore, it is wise for people with an animal allergy to check with
the landlord or previous owner to find out if furry pets had lived
previously on the premises.
Click
here to find solutions to Animal Allergies
Chemical Sensitivity
Some
people report that they react to chemicals in their environment and
that these allergy-like reactions appear to result from exposure to a
wide variety of synthetic and natural substances, such as those found
in paints, carpeting, plastics, perfumes, cigarette smoke, and plants.
Although the symptoms may resemble some of the manifestations of
allergies, sensitivity to chemicals does not represent a true allergic
reaction involving IgE and the release of histamine or other chemicals.
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Diagnosing Allergic Diseases
People
with allergy symptoms, such as the runny nose of allergic rhinitis, may
at first suspect they have a cold -- but the "cold" lingers on. It is
important to see a doctor about any respiratory illness that lasts
longer than a week or two. When it appears that the symptoms are caused
by an allergy, the patient should see a physician who understands the
diagnosis and treatment of allergies. If the patient's medical history
indicates that the symptoms recur at the same time each year, the
physician will work under the theory that a seasonal allergen (like
pollen) is involved. Properly trained specialists recognize the
patterns of potential allergens common during local seasons and the
association between these patterns and symptoms. The medical history
suggests which allergens are the likely culprits. The doctor also will
examine the mucous membranes, which often appear swollen and pale or
bluish in persons with allergic conditions.
Air Conditioners and Filters
When
possible, an allergic person should use air conditioners inside the
home or in a car to help prevent pollen and mold allergens from
entering. Various types of air-filtering devices made with fiber glass
or electrically charged plates may help reduce allergens produced in
the home. These can be added to the heating and cooling systems. In
addition, portable devices that can be used in individual rooms are
especially helpful in reducing animal allergens.
An
allergy specialist can suggest which kind of filter is best for the
home of a particular patient. The airflow should be sufficient to
exchange the air in the room five or six times per hour; therefore, the
size and efficiency of the filtering device should be determined in
part by the size of the room.
Very
small air cleaners cannot remove dust and pollen. Buyers of
electrostatic precipitators should compare the machine's ozone output
with Federal standards. Ozone can irritate the nose and airways of
persons with allergies, especially those with asthma, and can increase
the allergy symptoms. Other kinds of air filters such as HEPA filters
do not release ozone into the air. HEPA filters require adequate air
flow to force air through them.
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