What causes seasonal allergic rhinitis?

Seasonal allergic rhinitis is caused by your body's reaction to seasonal allergens - usually things like pollen from trees, grass, or weeds. In people with seasonal allergic rhinitis, the immune system overreacts to these harmless substances and identifies them as a threat. Your body fights back by releasing chemicals like histamine, which causes the sneezing and runny nose that are typical symptoms of seasonal allergic rhinitis.