Pollen is a very fine powder produced by trees and other plants to help grow and reproduce themselves. Because of its microscopic size, it travels easily through the air. Everyone breathes in tree pollen, but not everyone reacts to it. If you have a pollen allergy and go outside on a day when the pollen count is high, you’re likely to experience irritating symptoms like watery eyes or a runny nose.

Tree pollen, like grass and weed pollen, can travel far on windy days, so your reactions may not be because of the trees in your yard or neighborhood. The source of your allergies could actually come from trees miles away.