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Something in the Air: Airborne
Allergens
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.
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.
What is an allergic reaction?
Normally, the immune system functions as the body's defense
against invading agents such as bacteria and viruses. In most
allergic reactions, however, the immune system is responding
to a false alarm. When an allergic person first comes into contact
with an allergen, the immune system treats the allergen as an
invader and mobilizes to attack. The immune system does this
by generating large amounts of a type of antibody (a disease-fighting
protein) called immunoglobin E, or IgE. Each IgE antibody is
specific for one particular allergenic (allergy-producing) substance.
In the case of pollen allergy, the antibody is specific for
each type of pollen: one type of antibody may be produced to
react against oak pollen and another against ragweed pollen,
for example.
These IgE molecules are special because IgE is the only class
of antibody that attaches tightly to the body's mast cells,
which are tissue cells, and to basophils, which are blood cells.
When the allergen next encounters its specific IgE, it attaches
to the antibody like a key fitting into a lock, signaling the
cell to which the IgE is attached to release (and in some cases
to produce) powerful inflammatory chemicals like histamine,
cytokines, and leukotrienes. These chemicals act on tissues
in various parts of the body, such as the respiratory system,
and cause the symptoms of allergy.
Some people with allergy develop asthma. The symptoms of asthma
include coughing, wheezing, and shortness of breath due to a
narrowing of the bronchial passages (airways) in the lungs,
and to excess mucus production and inflammation. Asthma can
be disabling and sometimes can be fatal. If wheezing and shortness
of breath accompany allergy symptoms, it is a signal that the
bronchial tubes also have become involved, indicating the need
for medical attention. [top]
Symptoms of Allergies
to Airborne Substances
The signs and symptoms are familiar to many:
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Sneezing often accompanied by a runny or clogged nose
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Coughing and postnasal drip
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Itching eyes, nose, and throat
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Allergic shiners (dark circles under the eyes caused
by increased blood flow near the sinuses)
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The "allergic salute" (in a child, persistent
upward rubbing of the nose that causes a crease mark on
the nose)
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Watering eyes
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Conjunctivitis (an inflammation of the membrane that
lines the eyelids, causing red-rimmed, swollen eyes, and
crusting of the eyelids).
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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.
Histamine also can cause sneezing, itching, irritation, and
excess mucus production, which can result in allergic rhinitis
(runny nose). Other chemicals made and released by mast cells,
including cytokines and leukotrienes, also contribute to allergic
symptoms. [top]
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 windborne
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.
What is pollen?
Plants produce microscopic round or oval pollen grains to reproduce.
In some species, the plant uses the pollen from its own flowers
to fertilize itself. Other types must be cross-pollinated; that
is, in order for fertilization to take place and seeds to form,
pollen must be transferred from the flower of one plant to that
of another plant of the same species. Insects do this job for
certain flowering plants, while other plants rely on wind transport.
The types of pollen that most commonly cause allergic reactions
are produced by the plain-looking plants (trees, grasses, and
weeds) that do not have showy flowers. These plants manufacture
small, light, dry pollen granules that are custom-made for wind
transport. Samples of ragweed pollen have been collected 400
miles out at sea and 2 miles high in the air. Because airborne
pollen is carried for long distances, it does little good to
rid an area of an offending plant--the pollen can drift in from
many miles away. In addition, most allergenic pollen comes from
plants that produce it in huge quantities. A single ragweed
plant can generate a million grains of pollen a day.
The chemical makeup of pollen is the basic factor that determines
whether it is likely to cause hay fever. For example, pine tree
pollen is produced in large amounts by a common tree, which
would make it a good candidate for causing allergy. The chemical
composition of pine pollen, however, appears to make it less
allergenic than other types. Because pine pollen is heavy, it
tends to fall straight down and does not scatter. Therefore,
it rarely reaches human noses.
Among North American plants, weeds are the most prolific producers
of allergenic pollen. Ragweed is the major culprit, but others
of importance are sagebrush, redroot pigweed, lamb's quarters,
Russian thistle (tumbleweed), and English plantain.
Grasses and trees, too, are important sources of allergenic
pollens. Although more than 1,000 species of grass grow in North
America, only a few produce highly allergenic pollen. These
include timothy grass, Kentucky bluegrass, Johnson grass, Bermuda
grass, redtop grass, orchard grass, and sweet vernal grass.
Trees that produce allergenic pollen include oak, ash, elm,
hickory, pecan, box elder, and mountain cedar.
It is common to hear people say that they are allergic to colorful
or scented flowers like roses. In fact, only florists, gardeners,
and others who have prolonged, close contact with flowers are
likely to become sensitized to pollen from these plants. Most
people have little contact with the large, heavy, waxy pollen
grains of many flowering plants because this type of pollen
is not carried by wind but by insects such as butterflies and
bees.
When do plants make pollen?
One of the most obvious features of pollen allergy is its seasonal
nature--people experience it symptoms only when the pollen grains
to which they are allergic are in the air. Each plant has a
pollinating period that is more or less the same from year to
year. Exactly when a plant starts to pollinate seems to depend
on the relative length of night and day--and therefore on geographical
location--rather than on the weather. (On the other hand, weather
conditions during pollination can affect the amount of pollen
produced and distributed in a specific year.) Thus, the farther
north you go, the later the pollinating period and the later
the allergy season.
A pollen count, which is familiar to many people from local
weather reports, is a measure of how much pollen is in the air.
This count represents the concentration of all the pollen (or
of one particular type, like ragweed) in the air in a certain
area at a specific time. It is expressed in grains of pollen
per square meter of air collected over 24 hours. Pollen counts
tend to be highest early in the morning on warm, dry, breezy
days and lowest during chilly, wet periods. Although a pollen
count is an approximate and fluctuating measure, it is useful
as a general guide for when it is advisable to stay indoors
and avoid contact with the pollen. [top]
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 subfreezing 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.
What is mold?
There are thousands of types of molds and yeast, the two groups
of plants in the fungus family. Yeasts are single cells that
divide to form clusters. Molds consist of many cells that grow
as branching threads called hyphae. Although both groups can
probably cause allergic reactions, only a small number of molds
are widely recognized offenders.
The seeds or reproductive particles of fungi are called spores.
They differ in size, shape, and color among species. Each spore
that germinates can give rise to new mold growth, which in turn
can produce millions of spores.
What is mold allergy?
When inhaled, microscopic fungal spores or, sometimes, fragments
of fungi may cause allergic rhinitis. Because they are so small,
mold spores may evade the protective mechanisms of the nose
and upper respiratory tract to reach the lungs.
In a small number of people, symptoms of mold allergy may be
brought on or worsened by eating certain foods, such as cheeses,
processed with fungi. Occasionally, mushrooms, dried fruits,
and foods containing yeast, soy sauce, or vinegar will produce
allergic symptoms. There is no known relationship, however,
between a respiratory allergy to the mold Penicillium
and an allergy to the drug penicillin, made from the mold.
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.
Hot spots of mold growth in the home include damp basements
and closets, bathrooms (especially shower stalls), places where
fresh food is stored, refrigerator drip trays, house plants,
air conditioners, humidifiers, garbage pails, mattresses, upholstered
furniture, and old foam rubber pillows.
Bakeries, breweries, barns, dairies, and greenhouses are favorite
places for molds to grow. Loggers, mill workers, carpenters,
furniture repairers, and upholsterers often work in moldy environments.
Which molds are allergenic?
Like pollens, mold spores are important airborne allergens
only if they are abundant, easily carried by air currents, and
allergenic in their chemical makeup. Found almost everywhere,
mold spores in some areas are so numerous they often outnumber
the pollens in the air. Fortunately, however, only a few dozen
different types are significant allergens.
In general, Alternaria and Cladosporium (Hormodendrum)
are the molds most commonly found both indoors and outdoors
throughout the United States. Aspergillus, Penicillium, Helminthosporium,
Epicoccum, Fusarium, Mucor, Rhizopus, and Aureobasidium
(Pullularia) are also common.
Are mold counts helpful?
Similar to pollen counts, mold counts may suggest the types
and relative quantities of fungi present at a certain time and
place. For several reasons, however, these counts probably cannot
be used as a constant guide for daily activities. One reason
is that the number and types of spores actually present in the
mold count may have changed considerably in 24 hours because
weather and spore dispersal are directly related. Many of the
common allergenic molds are of the dry spore type--they release
their spores during dry, windy weather. Other fungi need high
humidity, fog, or dew to release their spores. Although rain
washes many larger spores out of the air, it also causes some
smaller spores to be shot into the air.
In addition to the effect of day-to-day weather changes on
mold counts, spore populations may also differ between day and
night. Day favors dispersal by dry spore types and night favors
wet spore types.
Are there other mold-related disorders?
Fungi or microorganisms related to them may cause other health
problems similar to allergic diseases. Some kinds of Aspergillus
may cause several different illnesses, including both infections
and allergy. These fungi may lodge in the airways or a distant
part of the lung and grow until they form a compact sphere known
as a "fungus ball." In people with lung damage or
serious underlying illnesses, Aspergillus may grasp the
opportunity to invade the lungs or the whole body.
In some individuals, exposure to these fungi also can lead
to asthma or to a lung disease resembling severe inflammatory
asthma called allergic bronchopulmonary aspergillosis. This
latter condition, which occurs only in a minority of people
with asthma, is characterized by wheezing, low-grade fever,
and coughing up of brown-flecked masses or mucus plugs. Skin
testing, blood tests, X-rays, and examination of the sputum
for fungi can help establish the diagnosis. Corticosteroid drugs
are usually effective in treating this reaction; immunotherapy
(allergy shots) is not helpful. [top]
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 workplaces.
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.
Waste products of cockroaches are also an important cause of
allergy symptoms from household allergens, particularly in some
urban areas of the United States. [top]
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. [top]
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. [top]
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.
Skin Tests
Doctors use skin tests to determine whether a patient has IgE
antibodies in the skin that react to a specific allergen. The
doctor will use diluted extracts from allergens such as dust
mites, pollens, or molds commonly found in the local area. The
extract of each kind of allergen is injected under the patient's
skin or is applied to a tiny scratch or puncture made on the
patient's arm or back.
Skin tests are one way of measuring the level of IgE antibody
in a patient. With a positive reaction, a small, raised, reddened
area (called a wheal) with a surrounding flush (called a flare)
will appear at the test site. The size of the wheal can give
the physician an important diagnostic clue, but a positive reaction
does not prove that a particular pollen is the cause of a patient's
symptoms. Although such a reaction indicates that IgE antibody
to a specific allergen is present in the skin, respiratory symptoms
do not necessarily result.
Blood Tests
Although skin testing is the most sensitive and least costly
way to identify allergies in patients, some patients such as
those with widespread skin conditions like eczema should not
be tested using that method. There are other diagnostic tests
that use a blood sample from the patient to detect levels of
IgE antibody to a particular allergen. One such blood test is
called the RAST (radioallergosorbent test), which can be performed
when eczema is present or if a patient has taken medications
that interfere with skin testing. [top]
Treating People
with Allergic Diseases
Doctors use three general approaches to helping people with
allergies: advise them on ways to avoid the allergen as much
as possible, prescribe medication to relieve symptoms, and give
a series of allergy shots. Although there is no cure for allergies,
one of these strategies or a combination of them can provide
varying degrees of relief from allergy symptoms.
Avoidance
Complete avoidance of allergenic pollen or mold means moving
to a place where the offending substance does not grow and where
it is not present in the air. But even this extreme solution
may offer only temporary relief since a person who is sensitive
to a specific pollen or mold may subsequently develop allergies
to new allergens after repeated exposure. For example, people
allergic to ragweed may leave their ragweed-ridden communities
and relocate to areas where ragweed does not grow, only to develop
allergies to other weeds or even to grasses or trees in their
new surroundings. Because relocating is not a reliable solution,
allergy specialists do not encourage this approach.
There are other ways to evade the offending pollen: remaining
indoors in the morning, for example, when the outdoor pollen
levels are highest. Sunny, windy days can be especially troublesome.
If individuals with pollen allergy must work outdoors, they
can wear face masks designed to filter pollen out of the air
and keep it from reaching their nasal passages. As another approach,
some people take their vacations at the height of the expected
pollinating period and choose a location where such exposure
would be minimal. The seashore, for example, may be an effective
retreat for many with pollen allergies.
Mold allergens can be difficult to avoid, but some steps can
be taken to at least reduce exposure to them. First, the allergy
sufferer should avoid those hot spots mentioned earlier where
molds tend to be concentrated. The lawn should be mowed and
leaves should be raked up, but someone other than the allergic
person should do these chores. If such work cannot be delegated,
wearing a tightly fitting dust mask can greatly reduce exposure
and resulting symptoms. Travel in the country, especially on
dry, windy days or while crops are being harvested, should be
avoided as should walks through tall vegetation. A summer cabin
closed up all winter is probably full of molds and should be
aired out and cleaned before a mold-sensitive person stays there.
Around the home, a dehumidifier will help dry out the basement,
but the water extracted from the air must be removed frequently
to prevent mold growth in the machine.
Those with dust mite allergy should pay careful attention to
dust-proofing their bedrooms. The worst things to have in the
bedroom are wall-to-wall carpets, venetian blinds, down-filled
blankets, feather pillows, heating vents with forced hot air,
dogs, cats, and closets full of clothing. Shades are preferred
over venetian blinds because they do not trap dust. Curtains
can be used if they are washed periodically in hot water to
kill the dust mites. Most important, bedding should be encased
in a zippered, plastic, airtight, and dust-proof cover.
Although shag carpets are the worst type for the dust mite-sensitive
person, all carpets trap dust and make dust control impossible.
In addition, vacuuming can contribute to the amount of dust,
unless the vacuum is equipped with a special high-efficiency
particulate air (HEPA) filter. Wall-to-wall carpets should be
replaced with washable throw rugs over hardwood, tile, or linoleum
floors. Rugs on concrete floors encourage dust mite growth and
should be avoided.
Reducing the amount of dust mites in a home may require new
cleaning techniques as well as some changes in furnishings to
eliminate dust collectors. Water is often the secret to effective
dust removal. Washable items should be washed often using water
hotter then 130 (degrees) Fahrenheit. Lower temperatures will
not kill dust mites. If the water temperature must be set at
a lower value, items can be washed at a commercial establishment
that uses high wash temperatures. Dusting with a damp cloth
or oiled mop should be done frequently.
The best way for a person allergic to pets, especially cats,
to avoid allergic reactions is to find another home for the
animal. There are, however, some suggestions that help lower
the levels of cat allergens in the air: bathe the cat weekly
and brush it more frequently (ideally, this should be done by
someone other than the allergic person), remove carpets and
soft furnishings, and use a vacuum cleaner with a high-efficiency
filter and a room air cleaner (see section below). Wearing a
face mask while house and cat cleaning and keeping the cat out
of the bedroom are other methods that allow many people to live
more happily with their pets.
Irritants such as chemicals can worsen airborne allergy symptoms
and should be avoided as much as possible. For example, during
periods of high pollen levels, people with pollen allergy should
try to avoid unnecessary exposure to irritants such as insect
sprays, tobacco smoke, air pollution, and fresh tar or paint.
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 fiberglass 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. Before buying a filtering
device, the patient should rent one and use it in a closed room
(the bedroom, for instance) for a month or two to see whether
allergy symptoms diminish. 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.
Persons with allergies should be wary of exaggerated claims
for appliances that cannot really clean the air. Very small
air cleaners cannot remove dust and pollen--and no air purifier
can prevent viral or bacterial diseases such as influenza, pneumonia,
or tuberculosis. 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, however, require adequate
air flow to force air through them.
Medications
For people who find they cannot adequately avoid airborne allergens,
the symptoms often can be controlled with medications. Effective
medications that can be prescribed by a physician include antihistamines
and topical nasal steroids--either of which can be used alone
or in combination. Many effective antihistamines and decongestants
also are available without a prescription.
Antihistamines. As the name
indicates, an antihistamine counters the effects of histamine,
which is released by the mast cells in the body's tissues and
contributes to allergy symptoms. For many years, antihistamines
have proven useful in relieving sneezing and itching in the
nose, throat, and eyes, and in reducing nasal swelling and drainage.
Many people who take antihistamines experience some distressing
side effects: drowsiness and loss of alertness and coordination.
In children, such reactions can be misinterpreted as behavior
problems. During the last few years, however, antihistamines
that cause fewer of these side effects have become available
by prescription. These non-sedating antihistamines are as effective
as other antihistamines in preventing histamine-induced symptoms,
but do so without causing sleepiness. Some of these non-sedating
antihistamines, however, can have serious side effects, particularly
if they are taken with certain other drugs. A patient should
always let the doctor know what other medications he/she is
taking.
Topical nasal steroids.
This medication should not be confused with anabolic steroids,
which are sometimes used by athletes to enlarge muscle mass
and can have serious side effects. Topical nasal steroids are
anti-inflammatory drugs that stop the allergic reaction. In
addition to other beneficial actions, they reduce the number
of mast cells in the nose and reduce mucus secretion and nasal
swelling. The combination of antihistamines and nasal steroids
is a very effective way to treat allergic rhinitis, especially
in people with moderate or severe allergic rhinitis. Although
topical nasal steroids can have side effects, they are safe
when used at recommended doses. Some of the newer agents are
even safer than older ones.
Cromolyn sodium. Cromolyn
sodium for allergic rhinitis is a nasal spray that in some people
helps to prevent allergic reactions from starting. When administered
as a nasal spray, it can safely inhibit the release of chemicals
like histamine from the mast cell. It has few side effects when
used as directed, and significantly helps some patients with
allergies.
Decongestants. Sometimes
re-establishing drainage of the nasal passages will help to
relieve symptoms such as congestion, swelling, excess secretions,
and discomfort in the sinus areas that can be caused by nasal
allergies. (These sinus areas are hollow air spaces located
within the bones of the skull surrounding the nose.) The doctor
may recommend using oral or nasal decongestants to reduce congestion
along with an antihistamine to control allerigic symptoms. Over-the-counter
and prescription decongestant nose drops and sprays, however,
should not be used for more than a few days. When used for longer
periods, these drugs can lead to even more congestion and swelling
of the nasal passages.
Immunotherapy
Immunotherapy, or a series of allergy shots, is the only available
treatment that has a chance of reducing the allergy symptoms
over a longer period of time. Patients receive subcutaneous
(under the skin) injections of increasing concentrations of
the allergen(s) to which they are sensitive. These injections
reduce the amount of IgE antibodies in the blood and cause the
body to make a protective antibody called IgG. Many patients
with allergic rhinitis will have a significant reduction in
their hay fever symptoms and in their need for medication within
12 months of starting immunotherapy. Patients who benefit from
immunotherapy may continue it for three years and then consider
stopping. Although many patients are able to stop the injections
with good, long-term results, some do get worse after immunotherapy
is stopped. As better allergens for immunotherapy are produced,
this technique will become an even more effective treatment.
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Allergy Research
The National Institute of Allergy and Infectious Diseases (NIAID)
conducts and supports research on allergies focused on understanding
what happens to the body during the allergic process--the sequence
of events leading to the allergic response and the factors responsible
for allergic diseases. This understanding will lead to better
methods of diagnosing, preventing, and treating allergies.
NIAID supports a network of Asthma, Allergic and Immunologic
Diseases Cooperative Research Centers throughout the United
States. The centers encourage close coordination among scientists
studying basic and clinical immunology, genetics, biochemistry,
pharmacology, and environmental science. This interdisciplinary
approach helps move research knowledge as quickly as possible
from research scientists to physicians and their allergy patients.
Educating patients and health care workers is an important
tool in controlling allergic diseases. All of these research
centers conduct and evaluate educational programs focused on
methods to control allergic diseases.
Researchers participating in NIAID's National Cooperative Inner-City
Asthma Study are examining ways to prevent asthma in minority
children in inner-city environments. Asthma, a major cause of
illness and hospitalizations among these children, is provoked
by a number of possible factors, including allergies to airborne
substances.
Although several factors provoke allergic responses, scientists
know that heredity is a major influence on who will develop
an allergy. Therefore, researchers are trying to identify and
describe the genes that make a person susceptible to allergic
diseases.
Some studies are aimed at seeking better ways to diagnose and
treat people with allergic diseases and to better understand
the factors that regulate IgE production in order to reduce
the allergic response in patients. Several research institutions
are focusing on ways to influence the cells that participate
in the allergic response.
Because researchers are becoming increasingly aware of the
role of environmental factors in allergies, they are evaluating
ways to control environmental exposures to allergens and pollutants
to prevent allergic disease.
These studies offer the promise of improving treatment and
control of allergic diseases and the hope that one day allergic
diseases will be preventable as well. [top]
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