Hay fever is caused by an allergic reaction to pollen. When it comes into contact with the mouth, eyes, nose or throat, the body reacts by making specific antibodies. Hay fever affects people at different times depending on which pollen they are allergic to.
This is a companion discussion topic for the original article at https://patient.info/news-and-features/the-pros-and-cons-of-the-hay-fever-injection