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Allergies Health Center

Ragweed Pollen and Fall Allergies

Most cases of hay fever are caused by allergies to ragweed.
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By David Freeman
WebMD Feature

Summer is ending, you’re heading into fall. But you’re still sneezing and sniffling all day and into the night. What’s going on?

Odds are you’re among the 10% to 30% of Americans who suffer from hay fever, or allergic rhinitis. And most cases of hay fever are caused by an allergy to fall pollen from plants belonging to the genus Ambrosia -- more commonly known as ragweed.

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How Ragweed Causes Allergies

Like all allergies, ragweed allergy occurs when the body’s immune system mounts a vigorous response to a foreign substance that is actually harmless -- in this case, tiny grains of pollen released by maturing ragweed flowers.

“Your immune system reacts to them as if they were a threat,” says Nathanael S. Horne, MD, clinical assistant professor of medicine at New York Medical College in Valhalla and an allergy specialist in private practice in New York City.

Specialized immune cells start churning out antibodies to proteins in the pollen. The ensuing cascade of biochemical reactions floods the bloodstream with histamine, a compound that causes all-too-familiar allergy symptoms.

In addition to sneezing, sniffling, nasal congestion, and sleep disruption, ragweed allergy can cause red, puffy eyes, itchy throat, and even hives. Severe cases can lead to chronic sinus problems (sinusitis) and even asthma attacks.

Can You Avoid Ragweed? Just Try!

If people who are allergic to ragweed could avoid the pollen, they could, of course, avoid the symptoms, Alas, that’s easier said than done.

There are 17 different species of ragweed in the U.S. These plants are most common in the rural areas of the Eastern states and Midwest, but are found throughout the U.S.

Scientists estimate that a single ragweed plant can release one billion grains of pollen over the course of a single ragweed season. And the grains are so light that they float easily even on gentle breezes. Pollen has been detected as far as 400 miles out to sea and up to two miles up in the atmosphere.

“The reality is that there is not a corner of the country where there is no ragweed pollen,” says Christine B. Franzese, MD, assistant professor of otolaryngology at the University of Mississippi Medical Center and chief of otolaryngology at the G. V. “Sonny” Montgomery VA Medical Center, both in Jackson.

If that sounds bad, things may soon get even worse. Recent studies suggest that rising temperatures and carbon dioxide levels are extending ragweed season.

In most parts of the country, the season used to start in mid-August and run through September; now it seems to begin from the first of August through mid-October.

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