You have an allergy when your body believes that something harmless, such as peanuts or pollen, can hurt you. Your immune system overreacts. This can cause uncomfortable or even dangerous symptoms.
This is an allergic reaction to pollen. Pollen is a fine powder that comes from trees, grass and weeds. Different people are allergic to different types of pollen, and they react to it in different ways. Hay fever can be a real nuisance.
