It's the season for sneezing

Q: I have suffered from seasonal allergies in the past. I am usually able to control the symptoms with medication, but each year feels worse than the last. What causes my allergies and why do they seem to be getting worse over time?

A: The seasonal allergies you are experiencing are known in the medical community as allergic rhinitis. You may have also heard allergies referred to as "hay fever," though grasses, the main component of the general term "hay," are not the only plants involved.

Seasonal allergic rhinitis comes and goes as various plants come into bloom. If your symptoms occur in the spring, you are probably allergic to tree pollen. In the summer, grass and weed pollens are the likely cause. In the late summer and fall, ragweed is probably to blame. If your symptoms occur year-round (perennial allergic rhinitis), you are probably allergic to indoor allergens, such as dust mites, mold or animal dander.

Generally, the allergic reactions that cause symptoms occur when you breathe in airborne allergens, either outdoors or indoors. An allergen is any substance that triggers the immune system to mount an inflammatory reaction. In your case, the inflammatory process starts right in your nose. Immune system mast cells in the nasal tissue release chemicals such as histamine and leukotrienes. Blood vessels swell, causing nasal congestion, and mucus production soars, creating a runny nose. Sneezing and itchy eyes often accompany these symptoms.

Repeated exposure to allergens causes mucous membranes in your nose to become more and more sensitive to allergens over time. This means it takes smaller and smaller amounts of allergens to spark the allergic reaction, and thus your symptoms, worsen over the years.

Seasonal outdoor allergies are caused by pollen: the male reproductive cells of trees and flowering plants. Some pollens are too heavy to become airborne and rarely play a role in allergies. But the pollens of some flowers and many trees, grasses and weeds don't attract insects to help them spread, so they need to be light and dry to be carried by winds. Once the pollen is airborne, it is easily inhaled.

Pollen molecules are tiny and numerous. They contain allergens that dissolve when they come in contact with the moist mucous membranes in the nose and respiratory tract. It takes only a very small amount of pollen to trigger an allergic reaction. The spores of molds cause allergies in much the same way as airborne pollen.

Unless your allergies are very minor, it's a good idea to treat your allergic rhinitis with medication rather than suffer through it. Apart from helping you feel better, well-timed treatment will lessen the likelihood of complications arising from chronic allergic rhinitis, such as sinus infections and blocked ears. If you also have asthma, you may find that your asthma will improve if you treat your allergic rhinitis. About 38 percent of allergic rhinitis sufferers also have allergic asthma, which can add wheezing and breathing problems to the already annoying sneezing and sniffling.

Seasonal hay fever can be very debilitating. To reduce hay fever symptoms, start taking your allergy medicines (antihistamines, nasal steroids and so forth) several weeks before you anticipate allergy season will start. Research has shown that this approach is more effective than starting the medicines after you have already developed symptoms. In addition, make sure you take practical steps to reduce your exposure to outdoor molds and pollens.

Here are some ways to minimize your pollen exposure:

--Stay indoors when the pollen count is high, especially on dry, windy days.

--Stay indoors between 5 a.m. and 10 a.m., when airborne pollen is likely to be at its highest each day.

--Keep home windows closed at night, and turn on the air conditioner.

--Keep car windows closed when driving.

--Vacation at the coast during high-pollen season.

--Don't cut your grass; have someone else do it.

--Don't hang clothing and bedding outside to dry.

People who are very bothered by airborne allergens may wonder whether moving to another part of the country would make a difference. The answer is yes and no. In the short term, you can outrun your allergens and find temporary relief from the pollens you've grown sensitive to. But this relief is usually short-lived. Eventually, you are likely to develop a hypersensitivity to the pollens in your new locale and become subject to allergic attacks once more. Ultimately, relocation isn't a solution.

Fortunately, most cases of allergic rhinitis respond well to simple medications, and desensitization treatments (allergy shots) are available for people who need more help.

The Harvard Medical School Adviser is researched and written by the faculty and staff of Harvard Medical School. Visit www.health. harvard.edu/adviser.

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