Why pollen makes you sneeze

When it comes time to mate, trees, weeds, and grasses release thousands of pollen grains into the air — which can end up invading your nose, eyes, and lungs. If you're allergic, your immune system mistakes these harmless grains for a serious threat and releases histamine. That irritates your nose, causing you to sneeze the grains out, and produce mucus in an effort to expel them.