Airborne Allergens


SOMETHING IN THE AIR


U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES 

National Institutes of Health 

National Institute of Allergy and Infectious Diseases 
Airborne Allergens


SOMETHING IN THE AIR 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES 

National Institutes of Health 

National Institute of Allergy and Infectious Diseases 

NIH Publication No. 03-7045 

April 2003 

www.niaid.nih.gov 
Contents


1 Introduction 

4 Symptoms 

6 Pollen Allergy 

10 Mold Allergy 

14 Dust Mite Allergy 

16 Animal Allergy 

17 Chemical Sensitivity 

18 Diagnosis 

20 Prevention 

25 Treatment 

28 Allergy Research 

32 Glossary 

34 More Information 

Introduction


Sneezing is not always the symptom of a cold. Sometimes, 

it is an allergic reaction to something in the air. Health 

experts estimate that 35 million Americans suffer from 

upper respiratory tract symptoms that are allergic 

reactions to airborne allergens. Pollen allergy, commonly 

called hay fever, is one of the most common chronic 

diseases in the United States. Worldwide, airborne 

allergens cause the most problems for people with 

allergies. The respiratory symptoms of asthma, which 

affect approximately 11 million Americans, are often 

provoked by airborne allergens. 

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 

(NIAID) of the National Institutes of Health (an agency 

of the U.S. Department of Health and Human Services) 

supports and conducts research on allergic diseases. The 

goals of this research are to provide a better understanding 

of the causes of allergy, to improve methods for diagnosing 

and treating allergic reactions, and eventually to prevent 

allergies. 

This booklet summarizes what health experts know 

about the causes and symptoms of allergic reactions to 

airborne allergens, how health care providers diagnose 

and treat these reactions, and what medical researchers 

are doing to help people who suffer from these allergies. 

Note: Words in bold are defined in the glossary at the end of 

this booklet. 

1
What is an allergy? 

An allergy is a specific reaction of the body’s immune 

system 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 

• House dust mites 

• Mold spores 

• Food 

• Latex rubber 

• Insect venom 

• Medicines 

Why are some people allergic? 

Scientists think that some people inherit a tendency to 

be allergic from one or both parents. This means they 

are more likely to have allergies. They probably, however, 

do not inherit a tendency to be allergic to any specific 

allergen. Children are more likely to develop allergies 

if one or both parents have allergies. In addition, exposure 

to allergens at times when the body’s defenses are lowered 

or weakened, such as after a viral infection or during 

pregnancy, seems to contribute to developing allergies. 

2
What is an allergic reaction? 

Normally, the immune system functions as the body’s 

defense against invading germs 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 

gets ready to attack. 

The immune system does this by generating large 

amounts of a type of antibody called immunoglobulin E, 

or IgE. Each IgE antibody is specific for one particular 

substance. In the case of pollen allergy, each antibody is 

specific for one type of pollen. For example, the immune 

system may produce one type of antibody to react 

against oak pollen and another against ragweed pollen. 

The IgE molecules are special because IgE is the only 

type 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. This action signals the cell to which 

the IgE is attached to release (and, in some cases, to 

produce) powerful chemicals like histamine, which 

cause inflammation. These chemicals act on tissues 

in various parts of the body, such as the respiratory 

system, and cause the symptoms of allergy. 

3
Symptoms


The signs and symptoms of airborne allergies are 

familiar to many. 

•	 Sneezing, often with a runny or clogged nose 

•	 Coughing and postnasal drip 

•	 Itching eyes, nose, and throat 

•	 Watering eyes 

•	 Conjunctivitis 

•	 “Allergic shiners” (dark circles under the eyes 


caused by increased blood flow near the sinuses)


•	 “Allergic salute” (in a child, persistent upward 


rubbing of the nose that causes a crease mark 


on the nose)


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 in a person who is sensitive to 

airborne allergens. 

In sensitive people, as soon as the allergen lands on the 

lining inside the nose, a chain reaction occurs that leads 

the mast cells in these tissues to release histamine and 

other chemicals. The 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. 

4
Other chemicals released by mast cells, including 

cytokines and leukotrienes, also contribute to 

allergic symptoms. 

Some people with allergy develop asthma, which 

can be a very serious condition. The symptoms of 

asthma include 

• Coughing 

• Wheezing 

• Shortness of breath 

The shortness of breath is due to a narrowing of the 

airways in the lungs and to excess mucus production 

and inflammation. Asthma can be disabling and 

sometimes fatal. If wheezing and shortness of 

breath accompany allergy symptoms, it is a signal 

that the airways also have become involved. 

Is it an allergy or a cold? 

There is no good way to tell the difference between allergy 

symptoms of runny nose, coughing, and sneezing and cold 

symptoms. Allergy symptoms, however, may last longer than 

cold symptoms. Anyone who has any respiratory illness 

that lasts longer than a week or two should consult a health 

care provider. 

5
Pollen Allergy


Each spring, summer, and fall, tiny pollen grains are 

released from trees, weeds, and grasses. These grains 

hitch rides on currents of air. Although the mission of 

pollen is to fertilize parts of other plants, many never 

reach their targets. Instead, pollen enters human noses 

and throats, triggering a type of seasonal allergic rhinitis 

called pollen allergy. Many people know this as hay fever. 

Of all the things that can cause an allergy, pollen is one 

of the most common. Many of the foods, medicines, or 

animals that cause allergies can be avoided to a great 

extent. Even insects and household dust are escapable. 

But short of staying indoors, with the windows closed, 

when the pollen count is high—and even that may not 

help—there is no easy way to avoid airborne pollen. 

What is pollen? 

Plants produce tiny—too tiny to see with the naked 

eye—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. 

Cross-pollination means that for fertilization to take 

place and seeds to form, pollen must be transferred 

from the flower of one plant to that of another of the 

same species. Insects do this job for certain flowering 

plants, while other plants rely on wind for transport. 

6
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 make small, light, dry pollen 

grains that are custom-made for wind 

transport. 

Amazingly, scientists have collected samples 

of ragweed pollen 400 miles out at sea and 

2 miles high in the air. Because airborne 

pollen can drift for many miles, it does little 

good to rid an area of an offending plant. 

In addition, most allergenic pollen comes 

from plants that produce it in huge quantities. For 

example, a single ragweed plant can generate a million 

grains of pollen a day. 

The type of allergens in the pollen is the main factor that 

determines whether the pollen 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. It is, however, a relatively rare cause 

of allergy because the type of allergens in pine pollen 

appear to make it less allergenic. 

Among North American plants, weeds are the most 

prolific producers of allergenic pollen. Ragweed is the 

major culprit, but other important sources are sagebrush, 

redroot pigweed, lamb’s quarters, Russian thistle 

(tumbleweed), and English plantain. 

7
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. 

It is common to hear people say 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 be sensitive to pollen 

from these plants. Most people have little contact with 

the large, heavy, waxy pollen grains of such flowering 

plants because this type of pollen is not carried by wind 

but by insects such as butterflies and bees. 

Some grasses that 

produce pollen 

• Timothy grass 

• Kentucky bluegrass 

• Johnson grass 

• Bermuda grass 

• Redtop grass 

• Orchard grass 

• Sweet vernal grass 

Some trees that 

produce pollen 

• Oak 

• Ash 

• Elm 

• Hickory 

• Pecan 

• Box elder 

• Mountain cedar 

8
When do plants make pollen? 

One of the most obvious features of pollen allergy is its 

seasonal nature—people have 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, 

in the Northern Hemisphere, the farther north you go, 

the later the start of the pollinating period and the later 

the start of the allergy season. 

A pollen count, 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 shown 

in grains of pollen per square meter of air collected 

over 24 hours. Pollen counts tend to be the highest early 

in the morning on warm, dry, breezy days and lowest 

during chilly, wet periods. Although the pollen count is 

an approximate measure that changes, it is useful as 

a general guide for when it may be wise to stay indoors 

and avoid contact with the pollen. 

9
Mold Allergy


What is mold? 

There are thousands of types of molds and yeasts in 

the fungus family. Yeasts are single cells that divide to 

form clusters. Molds are made of many cells that grow 

as branching threads called hyphae. Although both can 

probably cause allergic reactions, only a small number 

of molds are widely recognized offenders. 

The seeds or reproductive pieces of fungi are called 

spores. Spores differ in size, shape, and color among 

types of mold. 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, tiny fungal spores, or sometimes pieces 

of fungi, may cause allergic rhinitis. Because they are 

so small, mold spores also can 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 allergy symptoms. 

10
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, which makes 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. 

Molds also like bakeries, breweries, barns, dairies, 

and greenhouses. Loggers, mill workers, carpenters, 

furniture repairers, and upholsterers often work in 

moldy environments. 

What 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. 

11
In general, Alternaria and Cladosporium (Hormodendrum) 

are the molds most commonly found both indoors and 

outdoors in the United States. Aspergillus, Penicillium, 

Helminthosporium, Epicoccum, Fusarium, Mucor, 

Rhizopus, and Aureobasidium (Pullularia) are common 

as well. 

There is no relationship, however, between a respiratory 

allergy to the mold Penicillium and an allergy to the drug 

penicillin, which is made from mold. 

Are mold counts helpful? 

Similar to pollen counts, mold counts may suggest the 

types and number 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 distribution are 

directly related. Many 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 propelled into the air. 

12
In addition to the effect of weather changes during 

24-hour periods on mold counts, spore populations may 

also differ between day and night. Dry spore types are 

usually released during daytime, and wet spore types 

are usually released at night. 

Are there other mold-related disorders? 

Fungi or organisms 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 allergies. 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 people, 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 small number 

of people with asthma, causes 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 usually treat this reaction effectively. 

Immunotherapy (allergy shots) is not helpful. 

13
Dust Mite Allergy


Dust mite allergy is an allergy to a microscopic 

organism that lives in the dust found in all dwellings 

and workplaces. House dust, as well as some house 

furnishings, contains microscopic mites. Dust mites 

are perhaps the most common cause of perennial 

allergic rhinitis. House dust mite allergy usually 

produces symptoms similar to pollen allergy 

and also can produce symptoms of asthma. 

House dust 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. 

14
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 and 

materials such as 

•	 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 

•	 Other allergens peculiar to an individual 


house or building


Cockroaches are commonly found in crowded cities 

and in the southern United States. Certain proteins in 

cockroach feces and saliva also can be found in house 

dust. These proteins can cause allergic reactions or 

trigger asthma symptoms in some people, especially 

children. Cockroach allergens likely play a significant 

role in causing asthma in many inner-city populations. 

15
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. Researchers have found, however, 

that the major allergens are proteins in the saliva. These 

proteins stick to the fur when the animal licks itself. 

Urine is also a source of allergy-causing proteins, as 

is the skin. 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, 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 2 years or more to develop 

and may not decrease until 6 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 4 to 6 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 lived on the premises. 

16
Chemical Sensitivity


Some people report that they react to chemicals in their 

environments and that these allergy-like reactions seem 

to result from exposure to a wide variety of synthetic 

and natural substances. Such substances can include 

those found in 

• Paints 

• Carpeting 

• Plastics 

• Perfumes 

• Cigarette smoke 

• Plants 

Although the symptoms may resemble those of allergies, 

sensitivity to chemicals does not represent a true allergic 

reaction involving IgE and the release of histamine or 

other chemicals. Rather than a reaction to an allergen, 

it is a reaction to a chemical irritant, which may affect 

people with allergies more than others. 

17
Diagnosis


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. Testing for allergies is the best 

way to find out if a person is allergic. 

Skin tests 

Allergists (doctors who specialize in allergic diseases) 

use skin tests to determine whether a person has IgE 

antibodies in the skin that react to a specific allergen. 

The allergist will use weakened 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 a person’s skin or is applied to a tiny 

scratch or puncture made on the arm or back. 

Skin tests are one way of measuring the level of IgE 

antibody in a person. With a positive reaction, a small, 

raised, reddened area, called a wheal (hive), with a 

surrounding flush, called a flare, will appear at the 

test site. The size of the wheal can give the doctor an 

important diagnostic clue, but a positive reaction does 

not prove that a particular allergen is the cause of 

symptoms. Although such a reaction indicates that IgE 

antibody to a specific allergen is present, respiratory 

symptoms do not necessarily result. 

18
Blood tests 

Skin testing is the most sensitive and least costly way 

to identify allergies. People with widespread skin 

conditions like eczema, however, should not be tested 

using this method. 

There are other diagnostic tests that use a blood sample 

to detect levels of IgE antibody to a particular allergen. 

One such blood test is called the radioallergosorbent 

test (RAST), which can be performed when eczema is 

present or if a person has taken medicines that interfere 

with skin testing. 

Some ways to handle airborne allergies 

• Avoid the allergen 

• Take medicine 

• Get allergy shots 

19
Prevention


Avoidance 

Pollen and Molds 

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. Even 

this extreme solution may offer only temporary relief 

because a person sensitive to a specific pollen or mold 

may develop allergies to new allergens after repeated 

exposure to them. 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 reduce exposure to 

offending pollens. 

•	 Remain indoors with the windows closed in the 

morning, for example, when the outdoor pollen 

levels are highest. Sunny, windy days can be 

especially troublesome. 

•	 Wear a face mask designed to filter pollen out of the 

air and keep it from reaching nasal passages, if you 

must work outdoors. 

•	 Take your vacation at the height of the expected 

pollinating period and choose a location where such 

exposure would be minimal. 

Vacationing at the seashore or on a cruise, for example, 

may be effective retreats for avoiding pollen allergies. 

20
House Dust 

If you have dust mite allergy, pay careful 

attention to dust-proofing your bedroom. 

The worst things to have in the bedroom are 

•	 Wall-to-wall carpet 

•	 Blinds 

•	 Down-filled blankets 

•	 Feather pillows 

•	 Stuffed animals 

•	 Heating vents with forced hot air 

•	 Dogs and cats 

•	 Closets full of clothing 

Carpets trap dust and make dust control impossible. 

•	 Shag carpets are the worst type of carpet for people 

who are sensitive to dust mites. 

•	 Vacuuming doesn’t get rid of dust mite proteins in 

furniture and carpeting, but redistributes them back 

into the room, unless the vacuum has a special HEPA 

(high-efficiency particulate air) filter. 

•	 Rugs on concrete floors encourage dust mite growth. 

If possible, replace wall-to-wall carpets with washable 

throw rugs over hardwood, tile, or linoleum floors, and 

wash the rugs frequently. 

21
Reducing the amount of dust mites in your home may 

mean new cleaning techniques as well as some changes 

in furnishings to eliminate dust collectors. Water is often 

the secret to effective dust removal. 

•	 Clean washable items, including throw rugs, often, 

using water hotter than 130 degrees Fahrenheit. Lower 

temperatures will not kill dust mites. 

•	 Clean washable items at a commercial establishment 

that uses high water temperature, if you cannot or 

do not want to set water temperature in your home at 

130 degrees. (There is a danger of getting scalded 

if the water is more than 120 degrees.) 

•	 Dust frequently with a damp cloth or oiled mop. 

If cockroaches are a problem in your home, the 

U.S. Environmental Protection Agency suggests 

some ways to get rid of them. 

•	 Do not leave food or garbage out. 

•	 Store food in airtight containers. 

•	 Clean all food crumbs or spilled liquids right away. 

•	 Try using poison baits, boric acid (for cockroaches), 

or traps first, before using pesticide sprays. 

If you use sprays: 

•	 Do not spray in food preparation or storage areas. 

•	 Do not spray in areas where children play or sleep. 

•	 Limit the spray to the infested area. 

•	 Follow instructions on the label carefully. 

•	 Make sure there is plenty of fresh air when you spray. 

•	 Keep the person with allergies or asthma out of the 

room while spraying. 

22
Pets 

If you or your child is allergic to furry pets, especially 

cats, the best way to avoid allergic reactions is to find 

them another home. If you are like most people who are 

attached to their pets, that is usually not a desirable option. 

There are ways, however, to help lower the levels of animal 

allergens in the air, which may reduce allergic reactions. 

•	 Bathe your cat weekly and brush it more frequently 

(ideally, a non-allergic person should do this). 

•	 Keep cats out of your bedroom. 

•	 Remove carpets and soft furnishings, which collect 

animal allergens. 

•	 Use a vacuum cleaner and room air cleaners with 

HEPA filters. 

•	 Wear a face mask while house and cat cleaning. 

Chemicals 

Irritants such as chemicals can worsen airborne allergy 

symptoms, and you should avoid them as much as 

possible. For example, if you have pollen allergy, avoid 

unnecessary exposure to irritants such as insect sprays, 

tobacco smoke, air pollution, and fresh tar or paint 

during periods of high pollen levels. 

Air Conditioners and Filters 

When possible, use air conditioners inside your home 

or 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. You can add these to 

your present heating and cooling system. In addition, 

portable devices that can be used in individual rooms are 

especially helpful in reducing animal allergens. 

23
An allergist can suggest which kind of filter is best for 

your home. Before buying a filtering device, rent one 

and use it in a closed room (the bedroom, for instance) 

for a month or two to see whether your 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. 

You should be wary of exaggerated claims for appliances 

that cannot really clean the air. Very small air cleaners 

cannot remove dust and pollen. No air purifier can 

prevent viral or bacterial diseases such as the flu, 

pneumonia, or tuberculosis. 

Before buying an electrostatic precipitator, you should 

compare the machine’s ozone output with Federal 

standards. Ozone can irritate the noses and airways of 

people with allergies, especially those with asthma, and 

can increase their 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. 

24
Treatment


Medicines 

If you cannot adequately avoid airborne allergens, 

your symptoms often can be controlled by medicines. 

You can buy medicines without a prescription that 

can relieve allergy symptoms. If, however, they don’t 

give you relief or they cause unwanted side effects 

such as sleepiness, your health care provider can 

prescribe antihistamines and topical nasal steroids. 

You can use either medicine alone or together. 

Antihistamines 

As the name indicates, an antihistamine counters the 

effects of histamine, which is released by the mast cells 

in your body’s tissues and contributes to your allergy 

symptoms. For many years, antihistamines have proven 

useful in relieving itching in the nose and eyes; sneezing; 

and in reducing nasal swelling and drainage. 

Many people who take antihistamines have some 

distressing side effects such as drowsiness and loss of 

alertness and coordination. Adults may interpret such 

reactions in children as behavior problems. 

Antihistamines that cause fewer of these side effects 

are available over-the-counter or by prescription. These 

non-sedating antihistamines are as effective as other 

antihistamines in preventing histamine-induced symptoms, 

but most do so without causing sleepiness. 

25
Topical Nasal Steroids 

You should not confuse topical nasal steroids with 

anabolic steroids, which athletes sometimes use to 

enlarge muscle mass and which can have serious side 

effects. The chemicals in nasal steroids are different 

from those in anabolic steroids. 

Topical nasal steroids are anti-inflammatory medicines 

that stop the allergic reaction. In addition to other helpful 

actions, they decrease 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 

if you have moderate or severe allergic rhinitis. 

Although topical nasal steroids can have side effects, 

they are safe when used at recommended doses. 

Cromolyn Sodium 

Cromolyn sodium is a nasal spray that in some people 

helps prevent allergic rhinitis from starting. When used 

as a nasal spray, it can safely stop the release of chemicals 

like histamine from mast cells. It has few side effects 

when used as directed and significantly helps some 

people manage their allergies. 

Decongestants 

Sometimes helping the nasal passages to drain away 

mucus will help relieve symptoms such as congestion, 

swelling, excess secretions, and discomfort in the sinus 

areas that can be caused by nasal allergies. Your doctor 

may recommend using oral or nasal decongestants 

to reduce congestion along with an antihistamine to 

control allergic symptoms. 

26
You should not, however, use over-the-counter or 

prescription decongestant nose drops and sprays for 

more than a few days. When used for longer periods, 

these medicines can lead to even more congestion 

and swelling of the nasal passages. Because of recent 

concern about the bad effects of decongestant sprays 

and drops, some have been removed from store shelves. 

Immunotherapy

Immunotherapy, or a series of allergy shots, is the only 

available treatment that has a chance of reducing your 

allergy symptoms over a longer period of time. You 

would receive subcutaneous (under the skin) injections 

of increasing concentrations of the allergen(s) to which 

you are sensitive. These injections reduce the level of 

IgE antibodies in the blood and cause the body to make 

a protective antibody called IgG. 

About 85 percent of people with allergic rhinitis will see 

their hay fever symptoms and need for medicines drop 

significantly within 12 months of starting immunotherapy. 

Those who benefit from allergy shots may continue it for 

3 years and then consider stopping. While many are able 

to stop the injections with good results lasting for several 

years, others do get worse after the shots are stopped. 

One research study shows that children treated for allergic 

rhinitis with immunotherapy were less likely to develop 

asthma. Researchers need to study this further, however. 

As researchers produce better allergens for immunotherapy, 

this technique will be become an even more effective 

treatment. 

27
Allergy Research 

Research on allergies is focused on understanding what 

happens to the human body during the allergic process— 

the sequence of events leading to the allergic response 

and the factors responsible for allergic diseases. 

Scientists supported by NIAID found that, during the 

first years of their lives, children raised in a house with 

two or more dogs or cats may be less likely to develop 

allergic diseases as compared with children raised without 

pets. The striking finding here is that high pet exposure 

early in life appears to protect some children from not 

only pet allergy but also other types of common allergies, 

such as allergy to house dust mites, ragweed, and grass. 

This new finding is changing the way scientists think 

about pet exposure. Scientists must now figure out how 

pet exposure causes a general shift of the immune system 

away from an allergic response. 

The results of this and a number of other studies 

suggest that bacteria carried by pets may be responsible 

for holding back the immune system's allergic response. 

These bacteria release molecules called endotoxin. Some 

researchers think endotoxin is the molecule responsible 

for shifting the developing immune system away from 

responding to allergens through a class of lymphocytes 

called Th-2 cells. (These cells are associated with 

allergic reactions.) Instead, endotoxin may stimulate 

the immune system to block allergic reactions. 

If scientists can find out exactly what it is about pets or 

the bacteria they carry that prevents the allergic response, 

they might be able to develop a new allergy treatment. 

28
Some studies are seeking better ways to diagnose as 

well as treat people with allergic diseases and to better 

understand the factors that regulate IgE production to 

reduce the allergic response. Several research institutions 

are focusing on ways to influence the cells that participate 

in the allergic response. 

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 the lab into the hands of doctors and their allergy 

patients. 

Educating patients and health care providers is an 

important tool in controlling allergic diseases. All of 

these research centers conduct and evaluate education 

programs focused on methods to control allergic diseases. 

Since 1991, researchers participating in NIAID’s 

Inner-City Asthma Study have been examining ways 

to treat asthma in minority children living 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. 

29
The success of NIAID’s model asthma program led the 

U.S. Centers for Disease Control and Prevention to award 

grants to help community-based health organizations 

throughout the United States implement the program. 

Based on the success of the first National Cooperative 

Inner-City Asthma Study, NIAID and the National 

Institute of Environmental Health Sciences, also part 

of NIH, started a second cooperative multicenter study 

in 1996. This study recruited children with asthma, aged 

4 to 11, to test the effectiveness of two interventions. 

One intervention uses a novel communication and 

doctor education system. Information about the children’s 

asthma severity is provided to their primary care 

physicians, with the intent that this information will help 

the doctors give the children the best care possible. 

The other intervention involves educating families about 

reducing exposure to passive cigarette smoke and to 

indoor allergens, including cockroach, house dust mite, 

and mold. Researchers are assessing the effectiveness of 

both interventions by evaluating their capacity to reduce 

the severity of asthma in these children. 

Early data show that by reducing allergen levels in 

children’s beds by one-third, investigators reduced by 

nearly one-quarter (22 percent) both the number of 

days the children wheezed and the number of days the 

children missed school. 

30
Although several factors provoke allergic responses, 

scientists know that heredity plays a major role in 

determining who will develop an allergy. Therefore, 

scientists are trying to identify and describe the genes 

that make a person susceptible to allergic diseases. 

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 the treatment 

and control of allergic diseases and the hope that one 

day allergic diseases will be preventable. 

31
Glossary


allergen—substance that causes an allergic reaction 

allergenic—describes a substance which produces 

an allergic reaction 

antibody—molecule tailor-made by the immune system 

to lock onto and destroy specific germs 

basophils—white blood cells that contribute to 

inflammatory reactions 

conjunctivitis—inflammation of the lining of the eyelid, 

causing red-rimmed, swollen eyes, and crusting 

of the eyelids 

genes—units of genetic material that carry the directions 

a cell uses to perform a specific function 

granules—small particles; in cells the particles typically 

include enzymes and other chemicals 

immune system—a complex network of specialized 

cells, tissues, and organs that defends the body against 

attacks by disease-causing organisms 

inflammation—an immune system process that stops 

the progression of disease-causing organisms 

lymphocytes—small white blood cells which are 

important parts of the immune system 

32
mast cells—granule-containing cells found in tissue 

molecules—the building blocks of a cell. Some examples 

are proteins, fats, and carbohydrates 

organism—an individual living thing 

perennial—describes something that occurs throughout 

the year 

rhinitis—inflammation of the nasal passages, which can 

cause a runny nose 

sinuses—hollow air spaces located within the bones 

of the skull surrounding the nose 

sputum—matter ejected from the lungs and windpipe 

through the mouth 

tissues—groups of similar cells joined to perform the 

same function 

upper respiratory tract—area of the body which 

includes the nasal passages, mouth, and throat 

33
More Information


National Institute of Allergy and Infectious Diseases 

National Institutes of Health 

31 Center Drive, MSC 2520 

Bethesda, Maryland 20892-2520 

301-496-5717 

www.niaid.nih.gov 

National Institute of Environmental Health Sciences 

National Institutes of Health 

P.O. Box 12233 

Research Triangle Park, North Carolina 27709 

919-541-3345 

www.niehs.nih.gov 

National Library of Medicine 

MedlinePlus 

8600 Rockville Pike 

Bethesda, Maryland 20894 

1-888-FIND-NLM (1-888-346-3656) or 301-594-5983 

www.medlineplus.gov

U.S. Environmental Protection Agency 

Indoor Air Quality Information Clearinghouse 

P.O. Box 37133 

Washington, D.C. 20013-7133 

1-800-438-4318 or 703-356-4020 

www.epa.gov 

34
Allergy and Asthma Network/Mothers of 

Asthmatics, Inc. 

2751 Prosperity Avenue, Suite 150 

Fairfax, Virginia 22031 

1-800-878-4403 

www.aanma.org 

American Academy of Allergy, Asthma & Immunology 

611 East Wells Street 

Milwaukee, Wisconsin 53202 

1-800-822-ASMA (1-800-822-2762) 

www.aaaai.org 

American College of Allergy, Asthma & Immunology 

85 W. Algonquin Road, Suite 550 

Arlington Heights, Illinois 60005 

1-800-842-7777 

www.acaai.org 

Asthma and Allergy Foundation of America 

1233 20th Street, NW, Suite 402 

Washington, D.C. 20036 

1-800-7-ASTHMA (1-800-727-8462) or 202-466-7643 

www.aafa.org 

National Allergy Bureau (pollen information) 

1-800-9-POLLEN (1-800-976-5536) 

www.aaaai.org/nab 

35
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES 

National Institutes of Health 

National Institute of Allergy and Infectious Diseases 

NIH Publication No. 03-7045 

April 2003 

www.niaid.nih.gov