Allergic rhinitis (hay fever) is perhaps the best-known allergy of all. Many people associate this type of allergy primarily with outdoor exposure to pollen. However, you may also experience significant levels of pollen at home, and these exposures can also trigger allergic rhinitis symptoms.
Most pollens are windborne; they can often blow indoors (typically through open windows and doors) and trigger allergic symptoms such as allergic rhinitis (hay fever) within your home, not just outdoors. Wind-pollinated trees, grasses, and weeds produce pollen during various times of the year.
What is pollen allergy?
The signs and symptoms of pollen allergy are familiar to many:
- Sneezing, the most common symptom, 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).
Free-floating pollen particles are easy to inhale, without even knowing it. In people who are not allergic to pollen, the mucus in the nasal passages simply moves these foreign particles to the throat, where they are swallowed or coughed out. But something different happens to a pollen-sensitive person.
As soon as the allergy-causing pollen lands on the mucous membranes of the nose, a chain reaction occurs that leads special cells in these tissues (called mast cells) 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.
Some people with pollen allergy can 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. If wheezing and shortness of breath accompany the hay fever symptoms, it is a signal that the bronchial tubes also have become involved, indicating the need for medical attention.
What is pollen?
|Pollen particles as seen through a microscope (click to enlarge)|
Plants produce the microscopic round or oval grains called pollen in order to reproduce. 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. 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. For 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.
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.
When do plants make pollen?
One of the most obvious features of pollen allergy is its seasonal nature - people experience its 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 sample pollen count (click to enlarge)|
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 expressed in grains of pollen per square meter of air collected over 24 hours. A pollen count is an approximate and fluctuating measure, but it is useful as a general guide.
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.
How is pollen allergy diagnosed?
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. 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 hypothesis that a seasonal allergen like pollen is involved.
|A doctor is performing an allergy skin test|
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.
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.
How is pollen allergy treated?
There are three general approaches to the treatment of pollen allergy:
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.
Complete avoidance of allergenic pollen means moving to a place where the offending plant does not grow and where its pollen is not present in the air. But even this extreme solution may offer only temporary relief since a person who is sensitive to one specific weed, tree, or grass pollen may often develop allergies to others after repeated exposure. Thus, persons 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 and trees in their new surroundings. Because relocating is not a reliable solution, allergy specialists strongly discourage this approach.
There are other ways to evade the offending pollen:
- Remain indoors when the outdoor pollen levels are highest. Sunny, and windy days can be especially troublesome. Avoid intense outdoor activities, such as exercise or strenuous work, during the early morning and late afternoon hours when pollen counts are highest.
- If persons with pollen allergy must work outdoors, they can wear a pollen and dust mask. Face masks are designed to filter pollen out of the air reaching person's 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.
- Wash your hair before going to bed to avoid getting pollen on your pillow.
- Use a clothes dryer instead of hanging the wash outside, where it acts as a filter trap for pollen.
- Air cleaners. Use of air conditioners and purifires inside the home or in a car can be quite helpful in reducing pollen levels. Make sure to clean and replace your air conditioner and air cleaner filters regularly. Also effective are various types of air-filtering devices, which can be added to the heating and cooling systems in the home.
- 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.
You can find more hints in the article on minimizing your exposure to pollen.
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:
- Antihistamines. As the name indicates, an antihistamine counters the effects of histamine, which contributes to the 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. Unfortunately, many people who take antihistamines experience some distressing side effects: drowsiness and loss of alertness and coordination.
- 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. Because these drugs can raise blood pressure, increase the heart rate, and cause nervousness in some people, persons with allergies should check with their doctors before using decongestants. 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 side effects. Corticosteroids relieve the symptoms of pollen allergy by reducing nasal inflammation and inhibiting mucus production. Locally active steroids 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. Unlike antihistamines or steroids, cromolyn sodium is believed to control allergic symptoms by preventing histamine release. 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.
- Nasal Irrigation is a safe and effective practice that can (and probably should) be performed daily. Also called jala neti, it began as an ancient practice in India and is now practiced worldwide. Nasal irrigation uses salt water to flush bacteria and dried mucus out of the nose and sinuses.
- Saline sprays look very much like nasal decongestant sprays, but instead of medication they contain a specially mixed saline solution. The solution moisturizes dry and irritated mucous membranes. Saline sprays do not flush out the nasal and sinus passages as much as a full irrigation.
- Steam inhalation is often used to break up mucus and reduce congestion. Steam can soothe and moisturize irritated nasal and sinus membranes, and unlike nasal irrigation it also helps soothe sore throats and chest congestion.
- Aromatherapy is often used with steam inhalation to provide extra relief. Aromatherapy takes essential oils (usually a combination of eucalyptus, lavender, peppermint, tea tree oil, and rosemary) and uses them to produce a soothing vapor that helps to alleviate allergy symptoms. While you can mix your own aromatherapy oils, it is recommended that you buy a product with the oils already mixed for you, that way you can ensure it having the proper balance of oils.
Immunotherapy (Injection Treatments)
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.
What if pollen allergy is not treated?
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.
Where to find more information?
Page last modified: 05/12/08
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