What is a seasonal allergy?

It's an inflammatory reaction to something in the environment that causes unpleasant symptoms, such as sniffles, sneezes and swollen sinuses.

How do they develop?

There's a genetic component to most allergies. If one of your parents has them, there's an almost 50 percent chance that you will, too. It takes repeated exposure for allergies to develop fully, so several seasons might pass before a condition like hay fever sets in - which is why most kids don't develop allergies until they're 4 or 5. Seasonal allergies continue to develop throughout life. "New allergies can occur in any decade, but generally they tend to peak at around age 20," says Linda Cox, chair of the immunotherapy and Diagnostic Committee of the American College of Allergy, Asthma & Immunology.

When do seasonal

allergies strike?

The season typically begins in early spring, when trees, including oak, cedar, elm, birch, ash, maple and walnut start to pollinate. Grasses, such as timothy, Bermuda, orchard and some bluegrasses germinate in late spring and early summer. Weeds, like sagebrush, tumbleweed and ragweed - by far the most prevalent seasonal allergen, affecting 75 percent of sufferers - kick in during late summer and early fall. Moldy leaves, an often overlooked allergen, can extend symptoms almost until winter.

How do you find out whether you're allergic and what you're allergic to?

A seasonal allergy can feel like a cold, with symptoms such as chronic congestion, a runny nose and itchy, watery eyes. But allergies produce a thinner nasal discharge, won't prompt a fever, are 14 times more likely than colds to trigger a migraine headache and tend to last longer. If you've been sniffling for weeks on end, it's probably time to get tested.

The skin-prick test is the most common. A doctor introduces a number of allergens, sometimes as many as 60, by quickly pricking the patient's arm or back. If redness, itching or swelling occurs within 15 minutes, there's an allergy match. Alternatively, or if that test is inconclusive, a doctor might try a more sensitive intradermal shot, which injects allergens a little deeper below the skin.

What are the most

effective treatments?

Without treatment, allergies may worsen over time. Allergic reactions can spread deep into the lungs, putting you at an increased risk for asthma. For mild to moderate allergies, drugs - some prescription, some over-the-counter - are usually enough. All work similarly by trying to stop a reaction in its tracks. "The earlier you hit the medicine cabinet, the better your results," says Daniel Ein, chief of the allergy division of George Washington University.

Here are the major drug categories.

Antihistamines prevent cells in the body from releasing histamines, which trigger the coldlike symptoms. Oral over-the-counter options are often combined with a decongestant (generally tagged with a D) for more relief.

Pros: Treat throat and nasal itching, watery eyes, a runny nose and sneezing.

Cons: Alone, they won't help congestion or inflammation. Some brands can cause drowsiness.

Nasal corticosteroids are stronger than antihistamines. These prescription sprays, like Flonase, block inflammation and have been shown in some clinical studies to be the most effective remedy for allergy symptoms. (An oral version is available for extreme cases.)

Pros: Very effective for congestion.

Cons: May take a week or so to bring noticeable improvement. There's also a higher risk of mild side effects - including nosebleeds, irritation and a burning sensation - than with other allergy medications.

Decongestants are nonprescription and fast-acting, and are available orally or as a nasal spray. They work by constricting blood vessels, which in turn reduces the amount of fluid leaked from the nose.

Pros: Instant relief from congestion.

Cons: Duration is temporary. While the nasal sprays, such as Afrin, act faster than oral alternatives, like Sudafed, most doctors discourage their use for more than three or four days because once you start, you'll need more and more to get the same relief.

When should I consider allergy shots?

If allergies send you to bed or medications produce unpleasant side effects, immunotherapy might be for you. This treatment builds up long-term immunity to one or many allergens by continually exposing patients to greater doses of them. Covered by most insurance plans, immunotherapy typically reduces symptoms by 90 percent. But it's a lot of work. Over three to six months and well before allergy season, patients receive injections of specific allergens in increasing concentrations. Then, once or twice a month over the next three years, patients get maintenance shots of the maximum concentration reached during the buildup phase. If you're needle-shy, ask your doctor about a method that substitutes under-the-tongue pills or drops.

What can I do at home to minimize symptoms?

* Check the pollen count and try to stay inside when levels are high. For current levels, go to the American Academy of Allergy, Asthma & Immunology's Web site (www.aaaai.org/nab). You can also sign up for an allergen report via e-mail.

* Close windows at night and delay morning jogs. Plants release pollen from 4 a.m. to 8 a.m., so the longer you stay inside during this period, the better.

* Run the air conditioner and invest in a HEPA (high-efficiency particulate air) filter, which is required to capture 99.97 percent of the particles passing through it. Because pollen from shoes, animal paws and other things can get embedded in carpets, consider replacing permanent carpets with washable throw rugs.

* Keep your lawn mowed short to prevent it from sprouting pollen-producing buds.

* Wear natural fibers. Synthetics, such as polyester and nylon, can create a pollen-attracting electric charge when rubbed.

* Shower and wash your hair before going to bed. Daytime pollen can collect on your body, meaning you'll be breathing it in all night.

* Breathe through your nose. When it comes to keeping out foreign bodies, noses are better designed than mouths.

* Avoid secondhand smoke. A study published in 2006 in the Journal of Allergy and Clinical Immunology found that exposure to secondhand smoke exacerbated allergic responses.

* Finally, clean the house often. Use vacuums, mops and microfiber dust cloths, which collect particles, rather than brooms, which recirculate them into the air. Buy pillowcases and mattress covers made from fabrics labeled "dustproof," and wash them frequently. Don't air-dry bedding or clothes, since damp cloth attracts pollen. And wipe down windowsills with a damp cloth before going to bed so you can breathe and rest easy at night.