ST. LOUIS — The arrival of spring is nothing to sneeze about. Except when the air is saturated with tree pollen.

And the air is full of the stuff right now.

Doctors say a mild winter and early tree pollination point to a nasty season ahead.

The allergy season was fairly mild until the middle of April, said Dr. Raymond Slavin, director of the division of allergy at St. Louis University School of Medicine. "Only people who were extremely sensitive to tree pollen had problems," he said. "As of (mid-April), it's really gotten profound."

Spring allergies are triggered by the release of tree pollen, which can bring on sneezing, nasal congestion, a runny nose, and an itchy nose and eyes.

About one in five area people suffers from allergies. Allergic rhinitis, or hay fever, is the most common.

Most people with a sensitivity to tree pollen will experience symptoms once the count hits 1,500 pollen grains per cubic meter of air, Slavin said.

When Jennifer Do first moved to St. Louis from Los Angeles two years ago, she was blown away by the area's impressive display of seasons. Now she's just blowing — her nose.

The seasonal metamorphosis "definitely is a downer," she said.

Do began experiencing allergy symptoms recently — a runny nose, sneezing, itching and burning eyes. She had mild symptoms her first year in St. Louis. This year has been far worse.

"It's a shame I can't go outside and just enjoy the weather," said Do, 23, a medical student at St. Louis University. "Last week I played tennis. As a result, I've got my allergies to deal with."

Dr. H. James Wedner has seen two waves of allergy patients so far this year. The early wave came in after a warm spell in February spurred pine, cypress and juniper trees to cast off pollen.

"Now we're definitely seeing the spring rush," said Wedner, chief of the division of allergy and immunology at Washington University School of Medicine.

Slavin prefers the term "allergic rhinitis" (runny nose and eyes) to describe spring allergies, rather than "hay fever," which is a misnomer. Hay is not a usual cause of spring allergies, and it does not cause fever.

Allergic rhinitis that occurs during a specific season is called "seasonal allergic rhinitis." When it occurs throughout the year, it is called "perennial allergic rhinitis." Common year-round allergy sources are pets, dust mites and cockroaches.

Allergies also can trigger asthma, unleashing a host of other unpleasant symptoms such as wheezing, shortness of breath and tightness in the chest.

The first line of defense is to reduce exposure to pollen.

"When the symptoms begin, the windows in the house should come down and the windows of the car should be closed," Slavin said. "If you protect yourself for the 10 to 12 hours you're indoors, that's a big, big help."

When avoidance isn't enough, over-the-counter medications can help. Some over-the-counter antihistamines, however, can cause drowsiness.

The next step for the allergy-weary is to try prescription medicine, such as a nasal spray. Nasal sprays contain steroids and other substances that can reduce the local inflammatory response in the nose. There also are eye drops that have similar effects on the eye.

Slavin says the vast majority of people will respond to a combination of medication and environmental controls, such as closing windows and turning on the air conditioner. For those who don't, an antihistamine-decongestant combination, or immunotherapy, known as allergy shots, can be an option.