Every year microscopic particles, known as pollen, are released into the air by different types of weeds, grasses, and trees. A single plant can release millions of grains of pollen into the air each day. These pollen particles are small, lightweight, and dry, making them ideal for wind transport. Scientists have collected samples of ragweed pollen 400 miles out at sea and 2 miles high in the air.
Everyone breathes in pollen. For most people, it's harmless and your body gets rid of it easily. But for millions of Americans, pollen causes an allergic reaction. You may have heard this called hay fever, seasonal allergic rhinitis, or pollen allergy.
For people with hay fever, when the pollen enters the nose, the body sends immune cells to attack the normally harmless pollen. This causes a release of natural chemicals, including histamine. These chemicals enter the surrounding tissue within the nose and eyes, causing inflammation and swelling. Sneezing; an itchy, runny nose; congestion; and/or red, itchy, watery eyes can result.
Not all pollen is created equal when it comes to causing allergies. For example, both pine trees and ragweed create lots of pollen. Yet pine tree pollen is not very allergenic, whereas ragweed pollen is highly allergenic.
Each plant has a pollinating period that is more or less the same from year to year, whether it be during the spring, summer, or fall. Trees are usually the first to pollinate, followed by grasses, then weeds. This means that hay fever is also seasonal. A person will have symptoms based on when the pollen grains to which they are allergic are in the air.
Location also plays a roll on when specific pollens are released, and how long that season lasts.
Finally, you might have seen, or heard, pollen counts during your local weather reports. A pollen count is a measure of how much pollen is in the air over a certain area. They are often separated into absent, low, moderate, high, and very high. A pollen count can represent the concentration of all the pollen, or of one particular category, like weeds, or even type, like ragweed. Pollen counts can also be shown as a number. This represents grains of pollen per square meter of air collected over 24 hours.
The pollen count can be useful as a general guide for when it may be wise to stay indoors and avoid contact with the pollen. Pollen counts tend to be the highest early in the morning on warm, dry, breezy days and lowest during chilly, wet periods.