SATURDAY, April 12 (HealthDay News) -- Spring is here, and so is allergy season for millions of Americans.

With a bit of planning, effort and common sense, many people can limit their suffering or perhaps even avoid it altogether, according to Dr. Mark Dykewicz, professor of internal medicine and chief of allergy and clinical immunology at the Saint Louis University School of Medicine.

For the most part, seasonal allergies are caused by airborne pollens -- very fine powder released by trees, grasses and weeds as they pollinate and fertilize other plants of the same kind. Molds in outdoor air can also contribute to seasonal allergies.

Although outdoor allergens can be present year-round in warmer climates, allergy season generally begins in late winter or early spring and runs through late summer or early fall. As the season progresses, different types of pollens are present to trigger allergic reactions, Dykewicz said.

Dykewicz cited five important steps that help anyone prevent or relieve symptoms when pollen or mold counts are peaking:

• Use over-the-counter antihistamines for relief. For some people, these drugs are very effective at reducing the classic symptoms of seasonal allergies, including sneezing, runny nose, itchy eyes and scratchy throat. Be aware that some older-generation antihistamines, such as Benadryl, can cause sleepiness and the impairment of thinking and driving. More recent formulations tend to cause no drowsiness (Claritin, for example) or less drowsiness (Zyrtec), Dykewicz said.
• Keep your home's doors and windows closed. You can't completely seal off your home, but keeping doors and windows closed can help prevent pollens and outdoor molds from entering. As the weather turns nicer, use the air conditioner rather than opening a window to bring in "fresh" air.
• Limit outdoor activity, particularly in the morning. Avoid being outdoors, especially to exercise, when pollen counts are high, or on windy days when pollen and molds are being blown about. In general, pollen counts are highest from about 5 a.m. to 10 a.m.
• When traveling by car, keep the windows up. Again, this helps keep out pollens, dust and mold.
• Take a shower and change clothes. Pollen can collect on clothes and in your hair, so when you've been outside for any significant amount of time, shower and change into fresh clothes as soon as you get home.

If you've followed those steps and you're still suffering, then it is time to see a doctor, Dykewicz said.

A variety of prescription medications can help reduce or block seasonal allergy symptoms, he said. These include other oral antihistamines and several classes of nasal sprays. Nasal sprays tend to be the most effective at relieving symptoms by helping reduce inflammation and counteracting the allergic response.

For harder-to-treat cases, Dykewicz said many patients benefit from allergy immunotherapy -- a long-term series of shots to desensitize a patient from specific allergens.

The good news is there's a lot you and your doctor can do to help relieve or prevent suffering caused by allergies, Dykewicz said in a prepared statement.

More information

The Asthma and Allergy Foundation has more about outdoor seasonal allergies.