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‘Off-the-Charts’ Pollen Counts Bring Misery to Millions

Posted Apr 19 2010 12:50pm

sneeze
HealthDay News

A cold winter followed by a sudden and sustained warming trend, not to mention the botanical blossoming that global warming has brought, has boosted pollen counts to near-record highs across the United States this spring, experts say.

All of that has led to one of the most miserable allergy seasons in recent memory for the 50 million Americans who find themselves suffering itchy eyes, runny noses and scratchy throats this time of year.

“In Atlanta, we recently saw the second highest pollen count ever 5,733. A level of 1,500 is considered very high, so this was off the charts,” explained meteorologist Carl Parker, from The Weather Channel. Pollen counts are measured in grains of pollen per cubic meter in a sample that’s collected over a 24-hour period.

As so often happens, weather is largely to blame.

“Timing is everything and, in a lot of years, you might have bouts of warm followed by cold. This year, across a lot of the country, we were cold for a long time, and then the air pattern warmed and it was like we flipped a switch,” Parker said.

Adding to the problem “is the same system that’s bringing in the warm air has also been blocking rainstorms from coming in, and normally, rain comes through and knocks the pollen down, clearing things out,” he said.

The pollen problem is primarily affecting areas east of the Rocky Mountains, said Parker. In the west, he noted, there are still areas that are getting snow.

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Each spring, summer, and fall, tiny pollen grains are released from trees, weeds, and grasses. These grains hitch rides on currents of air. Although the mission of pollen is to fertilize parts of other plants, many never reach their targets. Instead, pollen enters human noses and throats, triggering a type of seasonal allergic rhinitis called pollen allergy. Many people know this as hay fever.

Of all the things that can cause an allergy, pollen is one of the most common. Many of the foods, medicines, or animals that cause allergies can be avoided to a great extent. Even insects and household dust are escapable. But short of staying indoors, with the windows closed, when the pollen count is highand even that may not helpthere is no easy way to avoid airborne pollen.

Plants produce tinytoo tiny to see with the naked eyeround or oval pollen grains to reproduce. In some species, the plant uses the pollen from its own flowers to fertilize itself. Other types must be cross-pollinated. Cross-pollination means that for fertilization to take place and seeds to form, pollen must be transferred from the flower of one plant to that of another of the same species. Insects do this job for certain flowering plants, while other plants rely on wind for transport.

The types of pollen that most commonly cause allergic reactions are produced by the plain-looking plants (trees, grasses, and weeds) that do not have showy flowers. These plants make small, light, dry pollen grains that are custom-made for wind transport.

Amazingly, scientists have collected samples of ragweed pollen 400 miles out at sea and 2 miles high in the air. Because airborne pollen can drift for many miles, it does little good to rid an area of an offending plant. In addition, most allergenic pollen comes from plants that produce it in huge quantities. For example, a single ragweed plant can generate a million grains of pollen a day.

The type of allergens in the pollen is the main factor that determines whether the pollen is likely to cause hay fever. For example, pine tree pollen is produced in large amounts by a common tree, which would make it a good candidate for causing allergy. It is, however, a relatively rare cause of allergy because the type of allergens in pine pollen appear to make it less allergenic.

Among North American plants, weeds are the most prolific producers of allergenic pollen. Ragweed is the major culprit, but other important sources are sagebrush, redroot pigweed, lamb’s quarters, Russian thistle (tumbleweed), and English plantain.

Grasses and trees, too, are important sources of allergenic pollens. Although more than 1,000 species of grass grow in North America, only a few produce highly allergenic pollen.

It is common to hear people say they are allergic to colorful or scented flowers like roses. In fact, only florists, gardeners, and others who have prolonged, close contact with flowers are likely to be sensitive to pollen from these plants. Most people have little contact with the large, heavy, waxy pollen grains of such flowering plants because this type of pollen is not carried by wind but by insects such as butterflies and bees.

Timothy grass

Kentucky bluegrass

Johnson grass

Bermuda grass

Redtop grass

Orchard grass

Sweet vernal grass

Oak

Ash

Elm

Hickory

Pecan

Box elder

Mountain cedar

One of the most obvious features of pollen allergy is its seasonal naturepeople have symptoms only when the pollen grains to which they are allergic are in the air. Each plant has a pollinating period that is more or less the same from year to year. Exactly when a plant starts to pollinate seems to depend on the relative length of night and dayand therefore on geographical location rather than on the weather. On the other hand, weather conditions during pollination can affect the amount of pollen produced and distributed in a specific year. Thus, in the Northern Hemisphere, the farther north you go, the later the start of the pollinating period and the later the start of the allergy season.

A pollen count, familiar to many people from local weather reports, is a measure of how much pollen is in the air. This count represents the concentration of all the pollen (or of one particular type, like ragweed) in the air in a certain area at a specific time. It is shown in grains of pollen per square meter of air collected over 24 hours. Pollen counts tend to be the highest early in the morning on warm, dry, breezy days and lowest during chilly, wet periods. Although the pollen count is an approximate measure that changes, it is useful as a general guide for when it may be wise to stay indoors and avoid contact with the pollen.


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