Excerpts mainly from National Institutes of Health Publication No.87-493

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. At these sites, the pollen can trigger the allergic reaction that doctors call pollen allergy, or seasonal allergic rhinitis, and that 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 pervasive. Many of the foods, drugs, or animals that cause allergies can be avoided to a great extent; even insects and household dust are not inescapable. However, 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.


An allergy is a sensitivity to a normally harmless substance, one that does not bother most people. The allergen (the foreign substance that provokes a reaction) can be a food, dust particles, a drug, insect venom, or mold spores, as well as pollen. Allergic people often have a sensitivity to more than one substance.

Why are some people allergic to these substances while others are not?

Scientists think that people inherit a tendency to be allergic, although not to any specific allergen. Children of allergic parents are much more likely to develop allergies than other children. Even if only one parent has allergies, a child has a one in four chance of being allergic. Another factor in the development of allergies seems to be exposure to allergens at certain times when the body's defenses are lowered or weakened such as after a viral infection, during puberty, or during pregnancy. (However, some women find that during pregnancy their hay fever symptoms diminish.)


Normally, the immune system functions as the body's defense against invading agents (bacteria and viruses, for instance). In most allergic reactions, however, the immune system is responding to a false alarm. When allergic persons first come into contact with an allergen, their immune systems treat the allergen as an invader and mobilize to attack. The immune system does this by generating large amounts of a type of antibody (a protein) called immunoglobulin E, or IgE. (Only small amounts of IgE are produced in nonallergic people.) Each IgE antibody is specific for one particular allergen. In the case of pollen allergy, the antibody is specific for each type of pollen: one antibody may be produced to react against oak pollen and another against ragweed pollen, for example.

These IgE molecules attach themselves to the body's mast cells, which are tissue cells, and to basophils, which are cells in the blood. When the enemy allergen next encounters the IgE, the allergen attaches to the antibody like a key fitting into a lock, signalling the cell to which the IgE is attached to release (and in some cases to produce) powerful inflammatory chemicals like histamines, prostaglandins, leukotrienes, and others. The effects of these chemicals on various parts of the body cause the symptoms of allergy.


Plants produce the microscopic round or oval grains called pollen in order to reproduce. 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; for example, 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 (allergy-producing) 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 a particular type is likely to cause hay fever. or example, pine tree pollen is produced in large amounts by a common tree, which would make it a good candidate for causing an allergy. However, the chemical composition of pine pollen appears to make it less allergenic than other types. Moreover, because pine pollen tends to fall straight down and is not widely scattered, 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 there are more than 1,000 species of grass 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.


Each plant has a pollinating period that is more or less the same from year to year. xactly 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.

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 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 on warm, dry, breezy days and lowest during chilly, wet periods. Moreover, the pollen concentration in an area can be changed by population growth, land use, tree plantings and cutting, industrialization, and pollution.


The signs and symptoms of pollen allergy are familiar to many:
  • Sneezing, the most common, may be accompanied by a runny or clogged nose

  • Itching eyes, nose, and throat

  • Allergic shiners (dark circles under the eyes caused by restricted 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 eyes).

As soon as the allergy-causing pollen lands on the mucous membranes of the nose, a chain reaction occurs that leads the mast cells in these tissues to release histamine. This powerful chemical dilates the many small blood vessels in the nose. Fluids escape through these expanded vessel walls, which causes the nasal passages to swell and results in nasal congestion.

Histamine can also cause itching, irritation, and excess mucus production. Other chemicals, including prostaglandins and leukotrienes, also contribute to allergic symptoms.

Some people with pollen allergy develop asthma, a serious respiratory condition. While asthma may recur each year during pollen season, it can eventually become chronic. The symptoms of asthma include coughing, wheezing, shortness of breath due to a narrowing of the bronchial passages, and excess mucus production. Asthma can be disabling and can sometimes be fatal.


People with a pollen allergy may at first suspect they have a summer cold - but the "cold" lingers on. For any respiratory illness that lasts longer than a week or two, it is important to see a doctor.

Skin Tests

To find out which types of pollen are responsible, skin testing may be recommended using pollens commonly found in the local area. A diluted extract of each kind of pollen is applied to a scratch or puncture made on the patient's arm or back or injected under the patient's skin.

With a positive reaction, a small, raised, reddened area with a surrounding flush (called a wheal and flare) will appear at the test site. The size of the wheal can provide the physician with an important reaction 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 pollen is present in the skin, respiratory symptoms do not necessarily result.

Blood Tests

Skin testing is not advisable in some patients such as those with certain skin conditions. Diagnostic tests can be done using 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). Although the RAST offers some advantages over skin testing, it is expensive to perform, takes several weeks to yield results, and is somewhat less sensitive. Skin testing remains the most sensitive and least costly diagnostic tool.


There are three general approaches to the treatment of pollen allergy; avoidance of the allergen, medication to relieve symptoms, and immunotherapy or injection treatments (commonly called allergy shots). Although no cure for pollen allergy has yet been found, one of these strategies or a combination of them can provide various degrees of relief from allergy symptoms.


Remaining indoors in the morning, for example, when the outdoor pollen levels are highest. Sunny, windy days can be especially troublesome. If persons with pollen allergy must work outdoors, they can wear face masks designed to filter pollen out of the air 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.

Air conditioners and filters. Use of air conditioners inside the home or in a car can be quite helpful in reducing pollen levels. Also effective are various types of air-filtering devices. These can be added to the heating and cooling systems in the home. In addition, there are portable devices that can be used in individual rooms such as HEPA air cleaners or pollen restriction filter screens which fit into windows.

Avoiding Irritants. During periods of high pollen levels, people with pollen allergy should try to avoid unnecessary exposure to irritants such as dust, insect sprays, tobacco smoke, air pollution, and fresh tar or paint. Any of these can aggravate the symptoms of pollen allergy.


For people with seasonal allergies who find they cannot avoid pollen, the symptoms can often be controlled with medication available by prescription or over the counter.

Effective medications that can be prescribed by a physician include antihistamines, corticosteroids, and cromolyn sodium - any of which can be used alone or in combination. There are also many effective antihistamines and decongestants that are available without a prescription.

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. Several new types of antihistamines that cause fewer of these side effects are now being developed and marketed.

Nasal Decongestants. Over-the-counter products containing decongestants can be helpful in relieving blocked nasal passages. These drugs constrict the blood vessels in nasal tissue, lessening swelling and mucus production.

People with allergic rhinitis should avoid using decongestant nasal sprays because frequent or prolonged use can lead to a "rebound phenomenon," in which the initial effect of shrinking the nasal passages is followed by increased swelling and congestion. When this occurs, a person often will use the spray in higher doses, or more frequently, in an attempt to get relief from congestion. Instead of improving nasal congestion, however, such use of nasal sprays only intensifies the problem.

Corticosteroids. Until recently, corticosteroids, although very effective in controlling allergic disorders, were not widely used for pollen allergy because their prolonged use can result in serious sided effects. Corticosteroids relieve the symptoms of pollen allergy by reducing nasal inflammation and inhibiting mucus production. Locally active steroids that penetrate the nasal membrane are now available as nasal sprays in measured-dose spray bottles. When used this way, the drug affects only the nasal passages rather than the entire body. The side effects, which are minimal when the spray is used in recommended doses, can include nasal burning and dryness and a sore throat.

Cromolyn sodium. Another effective agent that is available by prescription as a nasal solution is cromolyn sodium. Unlike antihistamines or steroids, cromolyn sodium is believed to control allergic symptoms by preventing the mast cells from releasing histamine. In clinical trials, cromolyn sodium has been proven safe and effective and, in contrast to some other allergy medications, appears to cause no drowsiness. Unlike antihistamines and decongestants, corticosteroid nasal sprays and cromolyn sodium nasal solutions must be used for several days to weeks before there is any noticeable reduction in symptoms.

Combination therapy. Sometimes antihistamines, cromolyn sodium, or nasal corticosteroids are not effective when used alone, but when prescribed in combination, these agents can often provide significant, if not total, relief from hay fever.


If environmental control methods and medication prove to be inadequate to control a person's symptoms, a physician may recommend immunotherapy (commonly called allergy shots). The aim of this treatment is to increase the patient's tolerance to the particular pollen to which he or she is allergic.

Diluted extracts of the pollen are injected under the patient's skin. The patient receives small doses once or twice a week, working up to larger doses that are given less often. The size of the largest dose depends on the patient's tolerance and the treatment's effect on the patient's allergy symptoms. Since it takes time to build up tolerance, prolonged treatment may be needed before the patient's symptoms are relieved.

Immunotherapy is not without problems. It can be expensive, and may require months before improvement is apparent. Further, it does not work well for some people and, if the size of the dose or frequency of shots is not carefully monitored, the injections can cause allergic reactions. These reactions can be quite mild - redness and swelling at the site of the injection - or potentially serious systemic reactions such as hives, generalized swelling, or shock. Immunotherapy is therefore only one part of a physician's overall treatment plan for an allergic patient.


As anyone with allergies knows, allergic symptoms are annoying and, in severe cases, debilitating. As a rule, however, an allergy to pollen does not progress to serious pulmonary or other diseases. Occasionally, when pollen allergy is not treated, complications may occur. These include swelling of the nasal passages and eustachian tubes leading to the ears, which may prevent proper drainage and airflow and lead to secondary infection of the sinuses or to middle ear problems.