Does your nose itch? Do your eyes sting? Do you feel a tickle in your throat. Are you about to. . . AAAAACHOO! If you're sneezy, itchy and stuffy these days, you may be allergic to the pollen that's floating around in the air. Many people -- over 20 million Americans -- are sensitive to the pollen that trees, grass and ragweed produce during the spring and summer months.

These plants make pollen as part of their reproductive cycle. Individual pieces of pollen are so tiny that you could fit hundreds or even thousands of them on the dot at the end of this sentence. When there's pollen in the air, you get lots of it in your body with every breath you take.

In the Washington, D.C., area, there are a lot of culprits that cause pollen. Maple, birch, juniper, cedar and box elder trees do it. So do pigweed, ragweed, Bermuda grass, orchard grass and many more plants. It's pretty much impossible to avoid pollen around here. Some people have allergy symptoms only during the time of year when pollen is around. They have seasonal allergies. For them, pollen is an allergen -- a substance that causes an allergic reaction.

Other people have symptoms all year long. They have perennial allergies. For them, things like cat dander, dust and mold are allergens. When an allergen gets into you, your body goes to work to get rid of it. It acts as if the pollen is an invader that has to be destroyed. The body starts making chemicals called histamines. The histamine makes your eyes itch and your nose run. The lining of your nose and throat swell up and produce extra moisture. You start feeling sneezy and stuffy. AAAAACHOO! If you're allergic, breathing polluted air can make you feel even worse. "Air pollution is an added burden to allergy sufferers," says Dr. David P. Huston, a professor of medicine at Baylor College of Medicine in Houston, Tex. "The chemicals and smoke can definitely aggravate their symptoms."

Other than moving to the North Pole, what can allergic people do? The best thing is to avoid your allergens, but that isn't always possible. Pollen is so tiny that you may not even be able to see it in the air, which makes it hard to avoid. Your family could try special filtering equipment to clean the air inside your house, use air conditioning instead of keeping the windows open, and keep rooms as clean and free of dust as possible. You can also listen to the "pollen count" that's given on the weather report, and avoid exercising outside on very high-count days.

Children with never-ending "colds" might actually be suffering from allergies. Colds last only about a week or so, while allergies can hang on for several weeks or even months. Colds often bring fevers; allergies don't. But hay fever -- a common name for seasonal allergies -- can make you feel just as miserable as colds do, though. All that sneezing and itching makes you feel tired.

Simple skin tests and information about where and when allergic reactions happen can help doctors figure out what people are allergic to. Then, they can decide how to treat the allergies. Doctors can help. There are medicines that stop allergic reactions. Doctors can suggest pills or nasal sprays that can stop allergic reactions. But these medicines may not be good for children to take. Doctors recommend that parents check with their doctor before they give kids allergy medicines from the drugstore. A pill that can be effective for a grown-up can be too strong for a child to use. Allergic people can get a series of shots that gradually make them less sensitive to their allergens. Over time -- sometimes up to five years -- these shots actually change the way the body acts when it's exposed to an allergen. According to the University of Wisconsin Center for Health Sciences, allergy shots get rid of symptoms for about three-quarters of the people who get them.Tips for Parents

A free brochure "Living with Allergies," is available by writing to Baylor College of Medicine, P.O. Box 130567, Houston, Tex., 77219. A free eight-page coloring book, "Welcome to the Allergy Neighborhood" is available free by calling the Allergy Information Center and Hotline at 1-800-727-5400. By coloring in items that can make people sneeze (feather pillows, plants, dogs), the book helps kids identify allergens and provides reassurance about going to the allergist. It was produced by the makers of Nasalcrom, a prescription allergy blocker, but the book does not promote a specific product. The book, "Conquering Your Child's Allergies" by M. Eric Gershwin M.D. and Edwin L. Klingelhofer, M.D. (Addison-Wesley, $9.95) provides a useful reference guide for parents of children with allergies ranging from hay fever to eczema, asthma, and food allergies. Catherine O'Neill is a freelance children's writer.