Pollen 'Explosion' Has U.S. Sneezing

FAQ on Pollen and Allergy: Some Surprising Answers

Medically Reviewed by Laura J. Martin, MD on April 19, 2010
From the WebMD Archives

April 19, 2010 -- Pollen has choked most of the U.S. in an unusually intense spring allergy season.

Is it the worst ever? What can you do about it? Which allergy treatments work best, and how do they work? Prepare for some surprises in WebMD's pollen/allergy FAQ.

Is the 2010 spring pollen season the worst ever for allergy sufferers?

In some parts of the U.S. -- the tree-lined city of Atlanta, for example -- the amount of tree pollen in the air hit near-record levels.

"It's a pollen explosion," meteorologist Tim Ballisty tells WebMD. "In Atlanta, the pollen count was up in the 5,000s, when 120 is a high level. And other cities in the Southeast, the Midwest, and the Northeast had off-the-charts pollen levels, too."

What happened? A "perfect storm of conditions conducive to bring pollen into the air," arborist Peter Gerstenberger, senior advisor to the Tree Care Industry Association, tells WebMD. "It has a lot to do with temperatures over a period of time that can cause a tree to create a lot of pollen. It has a lot to do with wind speed, and it has a lot to do with precipitation."

This perfect storm, Ballisty says, had several ingredients:

  • A long, cold winter dumped huge amounts of snow and rain across much of the nation. Trees got plenty of water, unlike recent drought years in the Southeast.
  • Spring arrived late. When it came, it brought hot, dry, summer-like conditions "compressing the pollen season," according to horticulturist Amanda Campbell of the Atlanta Botanical Garden. Ballisty notes that this April broke 1,800 high-temperature records across the nation.
  • Spring was summer-like not only because temperatures were unusually high, but because a ridge of high pressure funneled moisture away from the eastern half of the nation for extended periods. Rain washes the pollen from the air. Although pollen levels quickly rebound after rain, dry periods keep pollen blowing in the wind.

So has this been the worst spring allergy season ever? No, says Gerry Kress, vice president of SDI, the medical data company behind and other health information tools.

As of mid-April, Kress says, SDI calculates that about 24.7 million Americans have been affected by pollen and, to a much smaller extent, mold. Last year at this time, the number was a bit higher: about 24.8 million spring allergy sufferers.

"Pollen counts are useless. What does a count of 2,000 really mean? So we say look at the number of people affected," Kress says. "And in certain parts of the country, like the Northeast, where it seems everyone says they're dying from the pollen, the rest of the country is about the same. ... It's just that in certain areas of the country, pollen just exploded."

Why does pollen cause allergies?

Of all the things that cause allergic reactions, pollen is the most widespread. Why? Mainly because it's so hard to avoid.

Few people are allergic to the heavy, waxy pollen from large flowers because it's carried by bees and other insects. But many trees and grasses use a much more primitive form of sexual reproduction: They literally cast their pollen to the winds so it will drift onto the plants' female sex organs.

Pollen from such trees and grasses is tiny, light, and dry -- perfect for floating on the wind, and, unfortunately, perfect for getting inhaled into your nose or stuck in your eye.

Once pollen sticks to your nose or eye, it releases the protein inside it. It's this protein that triggers allergic reactions.

There are two steps to this process. First, a person has to be sensitized to a particular pollen. The pollen protein is recognized by the immune system as a foreign invader and it makes a particular kind of antibody -- IgE -- to fight it off.

The second step occurs only in people already sensitized to a specific pollen protein. When the protein hits the nose or eye, a flood of IgE antibodies travel to mast cells in the nose. The IgE sits on the outside of mast cells and, when triggered by pollen protein, unleashes a flood of histamine and other factors that cause the immune responses we know as allergy.

How do allergy drugs work?

The most common kind of allergy drugs are antihistamines. Histamine is a chemical messenger that triggers allergy attacks by flipping switches on cells called histamine receptors. Antihistamines block these receptors.

But they can't block every histamine receptor on every cell, says Donald J. Dvorin, MD, an allergist with The Asthma Center in Philadelphia and director of the AAAAI pollen reporting stations in Philadelphia and Cherry Hill, N.J.

"The problem is they don't go to every cell," Dvorin tells WebMD. "And the blockade is only short term -- it only works for a certain half-life."

Intranasal antihistamines work a little better. They, too, block histamine receptors. But Dvorin says they also stabilize the membranes on mast cells, preventing the release of allergy-promoting factors and reducing swelling.

A third kind of allergy drug is a corticosteroid nasal spray. This drug has a more global effect on mast cells, suppressing their activity. They block the release not only of histamine but of other allergy-promoting factors.

What is the best treatment for pollen allergy?

The very best treatment for pollen allergy is to avoid pollen, Dvorin says.

"I can't tell you how many patients tell me that as soon as they go into an air-conditioned space, their symptoms get better," he says. "They know they can't be outdoors from 5 a.m. to 11 a.m. The morning is when the pollen is released most intensely. And there is a secondary peak after 4 p.m. for certain trees and grasses."

Different allergy drugs work best for different people. But in a 2010 analysis of clinical trials by Cleveland Clinic researchers, intranasal corticosteroid drugs worked nearly twice as well as oral and nasal antihistamines, which seemed to have about the same effect.

Dvorin notes that a person needs to take intranasal corticosteroids for three to seven days "before they really work."

He advises people who know they have spring allergies to see an allergist in the off season. Skin testing can reveal which types of pollen a person is allergic to -- allowing that person to begin treatment before those plants start to release pollen in the spring.

There's also a "priming effect," in which people become more and more sensitive to the pollen they're allergic to as the season goes on.

"Starting corticosteroid treatment early actually prevents the priming effect," Dvorin says. "If you treat early enough you reduce symptoms. Corticosteroids are the only products that prevent the peak of symptoms."

Allergy sufferers who get too little relief from allergy drugs may wish to consult an allergist about getting allergy shots, which can desensitize a person to the pollens to which they're allergic.

Show Sources


Benninger, M. Annals of Allergy, Asthma, & Immunology, January 2010; vol 104: pp 13-29.

MedicineNet web site: "Pollen Allergy, What Is It?"

American Academy of Allergy, Asthma & Immunology web site: "Tips to Remember: Outdoor Allergens."

Tim Ballisty, meteorologist,

Amanda Campbell, horticulturist and manager of display garden, Atlanta Botanical Garden.

Peter Gerstenberger, senior advisor, Tree Care Industry Association.

Donald J. Dvorin, MD, allergist, The Asthma Center, Philadelphia; director of AAAAI pollen reporting stations, Philadelphia and Cherry Hill, N.J.

Gerry Kress, vice president, SDI.

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