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Pollen 'Explosion' Has U.S. Sneezing

FAQ on Pollen and Allergy: Some Surprising Answers

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."

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