Deciding the pollen is dangerous, your immune system develops a small amount of antibodies to fight it off. Then the cells in your nose, eyes, throat and lungs called mast cells release histamines. Histamines tell your tissues to secrete fluids that make them irritated. That's when allergy symptoms occur. If your allergies are worse in some seasons than others, there's a good possibility you're allergic to pollen.
Plants pollinate at different times of the year and it varies from season to season.
Also, an early spring and late summer can be very problematic depending on where you live. Allergies are tricky because no two people suffer the same. That is why they are hard to treat. You may be allergic to more then one thing. This is known as Perennial Allergen because it doesn't change with the seasons.