Aside from pollens there are other inhaled allergens that affect our respiratory system.These are some of the top inhaled allergens.

1.tree pollen
2.grass pollen
3.weed pollen
4.mold spores
5.cat dander
6.dog dander
6.house dust mites.

But as you have asked about pollen allergy so it goes as....

Each Spring,Fall and Summer trees produce pollen.Consequently this is when pollen allergy takes its toll on us.The job of the pollens is to fertilize other plants but quite often pollen doesn't reach its target.Many times as your symptoms will attest pollen winds up entering our throats,noses making our lives difficult if not simply miserable.To make matters worse pollen is practically inescapable even If we seal off our house pollen will still find its way.
Interestingly plants with bright colored flowers usually don't bother pollen allergy sufferers.It is the plain looking trees and plants that cause the greatest allergy symptoms.
The trees that are most likely to produce pollen allergy are as follows.
Oak
Ash
Elm
Hickory
Pecan
Box elder
Mountain ceder.