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 defences 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.) People with pollen allergies often develop sensitivities to other troublemakers that are present all year such as dust and mold. Year-round allergens like these cause perennial allergic rhinitis, as distinguished from seasonal allergic rhinitis, or hay fever.

Normally, the immune system functions as the body’s defence 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 molecules attach themselves to the body’s mast cells, which are tissue cells, and to basophiles, 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.

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). 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 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. If
wheezing an 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.

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.

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: 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 made with fibreglass or electrically charged plates. 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. An allergy specialist can suggest which kind of filter is best for the home of a particular patient. Before buying a filtering device, it is wise to 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 air flow 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.

Devices that may not work. 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 asthmatics, and can increase the allergy symptoms.

Other kinds of air filters such as HEPA (high efficiency particulate air) filters do not release ozone into the air. 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. Antihistamines. As the name indicates, an antihistamine counters the effects of histamine, which, as described before, is released by the mast cells in the body’s tissues and 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.

But 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 behaviour 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. Nasal decongestants, although available as nasal sprays, may be taken orally; these include compounds such as ephedrine, phenyl-propanolamine hydrochloride, and pseudoephedrine hydrochloride. 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 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.