Pollen 'Explosion' Has U.S. Sneezing
FAQ on Pollen and Allergy: Some Surprising Answers
WebMD News Archive
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
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
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
"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."