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1. NIAID
National Institute of Allergy and Infectious Diseases | health information
Pollen Allergy
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
National Institutes of Health
National Institute of Allergy and Infectious Diseases
Of all the things that can cause an allergy, pollen is one of the most common. Many people know
pollen allergy as hay fever, but health experts usually refer to it as “seasonal allergic rhinitis.”
This simply means an allergy to pollen that makes your nose run during certain seasons.
An allergy is a specific reaction of your body’s immune system to a normally harmless substance.
People who have allergies often are sensitive to more than one substance. In addition to pollen from
plants, other airborne allergens that can cause allergic reactions include materials from house dust
mites, pet dander, and cockroaches.
Symptoms of pollen allergy include runny nose, sneezing, itchy eyes, congestion of the nose, and red
and watery eyes.
What Is Pollen?
Plants produce round pollen grains that must be moved from one plant to another of the same kind
for fertilization to occur. Individual grains are too tiny to see with the naked eye, but some can form
large, visible clusters.
Most of the pollen that causes allergic reactions comes from plants that don’t have showy flowers,
such as trees, weeds, and grasses. These plants make small, light, dry pollen grains that are made to
be carried by wind.
Because airborne pollen can drift for many miles, ridding a local area of an offending plant may not
help. Amazingly, scientists have collected samples of ragweed pollen 400 miles out at sea and 2 miles
high in the air. In addition, most allergy-causing pollen comes from plants that produce it in huge
quantities. For example, a single ragweed plant can generate a million grains of pollen every day.
The components of a pollen grain are the main factors that determine whether that pollen is likely to
cause allergic rhinitis. For example, pine tree pollen is produced in large amounts by a common tree,
but it is not a major cause of pollen allergy because the components of pine pollen are less likely to
cause an allergic reaction.
Among North American plants, weeds produce the largest amounts of allergenic pollen. Ragweed is
the major culprit, but other important sources of weed pollen come from sagebrush, redroot pigweed,
lamb’s quarters, Russian thistle (tumbleweed), and English plantain. Some species of grasses and trees
also produce highly allergenic pollen.

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Although some people may think they are allergic to
colorful or scented flowers like roses, it’s not usually the
case. Only florists, gardeners, and others who have close
contact with flowers over a long period of time are likely
to be sensitive to pollen from these plants. In fact, most
people have little contact with the large, heavy, and waxy
pollen grains of flowering plants because this type of pol-
len is not carried by wind, but by insects such as butter-
flies and bees.
When do plants make pollen?
One of the obvious features of pollen allergy is its sea-
sonal nature—people have symptoms only when the pol-
len grains to which they are allergic are in the air. Each
plant pollinates more or less at the same time 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. But weather conditions during pollination can
affect the amount of pollen produced and carried by the
wind in a specific year. For example, in the Northern
Hemisphere, areas farther north experience a later start
to the pollinating period and the pollen allergy season.
Some grasses that produce pollen
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Timothy grass
Kentucky bluegrass
Johnson grass
Bermuda grass
Redtop grass
Orchard grass
Sweet vernal grass
Some trees that produce pollen
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Oak
Ash
Elm
Hickory
Pecan
Box elder
Mountain cedar
What is a pollen count?
A pollen count, often reported by local weather stations or allergy Web sites, is a measure of how
much pollen is in the air. This count represents the concentration of all the pollen (or of one particu-
lar type, like ragweed) in the air in a certain area at a specific time. It is reported as grains of pollen
per cubic meter of air collected over 24 hours.
Pollen counts tend to be the highest early in the morning on warm, dry, breezy days and the lowest
during chilly, wet periods. Although the pollen count changes, it is useful as a general guide for when
it may be wise for you to stay indoors and avoid contact with that pollen.
Diagnosis
Skin test
A doctor with expertise in allergic diseases, known as an allergist, or other healthcare professional
will use the skin prick test to find out whether you have antibodies that react to a specific allergen.
These antibodies, produced by the immune system, attach to mast cells in your skin. When the aller-
gen binds to its antibody like a lock and key, the mast cells release histamine and other chemicals that
cause allergy symptoms. A skin test is simple, relatively safe, and the results are ready in minutes.
With a skin prick test, your healthcare professional uses a needle to place a tiny amount of pollen
extract (liquid substance) just below the surface of the skin on your lower arm or back. If you are

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allergic, there will be swelling or redness at the test
site. Although such a reaction shows that you produce
antibodies to a specific allergen, you might not have
the respiratory and eye symptoms (runny nose, sneez-
ing, itchy eyes) of an allergic reaction.
Blood tests
Instead of the skin test, your healthcare professional
can take a blood sample to measure the levels of pol-
len-specific antibodies your body produces.
As with skin testing, positive blood tests don’t neces-
sarily mean that you have pollen allergy. A person receiving a skin prick test. A number of
allergens can be tested with a skin prick test, including
ragweed and grass pollens.
Treatment
Medicines
Because it is nearly impossible to avoid contact with pollen, you might be able to control your symp-
toms with medicines. You can buy some allergy medicines without a prescription. Most over-the-
counter medicines are antihistamines. These medications are often helpful in people who have mild
disease. If these medicines don’t give you relief or they cause unwanted side effects, your healthcare
professional may write a prescription for a more powerful medicine. For example, you may be pre-
scribed a topical nasal steroid to take with an antihistamine. Some people with seasonal allergic
rhinitis develop complications, including asthma and sinusitis. If these complications develop, it’s
important to see a healthcare professional.
Antihistamines
Antihistamines have proven useful in relieving sneezing and itching in the nose and eyes and in
reducing swelling and drainage in the nose because of pollen allergy.
Many people who take some types of antihistamines, available over the counter or by prescription,
have some unwelcome side effects, such as drowsiness and loss of alertness and coordination. When
children have such reactions, adults may interpret those reactions as behavior problems.
Effective antihistamines that cause fewer of these side effects are available over the counter or by
prescription.
Topical nasal steroids
Topical nasal steroids are anti-inflammatory medicines that inhibit the allergic reaction. The combi-
nation of antihistamines and nasal steroids is a very effective way to treat pollen allergy, especially if
your reaction to pollen is moderate or severe.
You should not confuse topical nasal steroids with anabolic steroids, which athletes sometimes use
to improve their performance and which can have serious side effects. The chemicals in nasal steroids
are different from those in anabolic steroids.

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Although topical nasal steroids can have side effects, they are safe when used at the recommended
doses and for the recommended period of time.
Cromolyn sodium
Cromolyn sodium is a nasal spray that helps prevent allergic rhinitis from starting in some people.
When used as a nasal spray, it can safely inhibit the release of chemicals that cause allergy symptoms.
It has few side effects when used as directed and significantly helps some people manage their allergies.
Decongestants
Decongestants can help shrink your nasal passages. This, in turn, can help relieve congestion, swell-
ing, and general discomfort in the sinus areas caused by nasal allergies. Your healthcare professional
may recommend using oral or nasal decongestants to reduce congestion along with an antihistamine
to control your symptoms.
You shouldn’t use over-the-counter or prescription decongestant nose drops and sprays for more
than a few days. When you use them for longer periods, these medicines can lead to even more con-
gestion and swelling inside your nose and sinuses.
Allergy shots
Currently, a series of allergy shots, or allergen immunotherapy, is the only available treatment that
has a chance of providing a long-lasting benefit, for several years, even after the treatment is stopped.
Allergy shots are given as subcutaneous (under the skin) injections. They contain increasing concen-
trations of the pollen allergen(s) to which you are sensitive. These shots reduce the level of antibod-
ies to pollen in your blood and cause your body to make another protective antibody called IgG.
Because these shots may have significant side effects, people need to stay in the healthcare profes-
sional’s office for a period of time after receiving the shots.
Health experts recommend that people who benefit from allergy shots continue receiving them for
3 years and then consider stopping them with the guidance of an allergy specialist. Although many
people are able to stop the injections with good results lasting for several years, others do get worse
after the shots are stopped.
As researchers improve allergy shots, they promise to become an even more effective treatment.
More Information
Contact NIAID for more information about pollen allergy:
National Institute of Allergy and Infectious Diseases
National Institutes of Health
6610 Rockledge Drive, MSC 6612
Bethesda, MD 20892-6612
866-284-0147 or 301-496-5717
E-mail: ocpostoffice@niaid.nih.gov
www.niaid.nih.gov
U.S. DEPARTMENT OF HEALTH
AND HUMAN SERVICES
National Institutes of Health
National Institute of Allergy
and Infectious Diseases
www.niaid.nih.gov
January 2012