ELI5 Allergies - What causes us to get allergic reactions? Are there more allergy incidences today than 20yrs ago?

Why do people have allergies? Why does an allergic reaction cause our bodies to block up our main means of breathing? Why does it seem like so many more children today have severe food allergies than there were 20 years ago?   ... We explain like i'm five!   Thank you to the r/explainlikeimfive community, and specifically the following reddit users whose questions and responses formed the basis of this conversation: fsjd150, wantagh, goldilungs, thatniceguynoah, tinglesonmahdingus & n8thegr8   If you have suggestions, comments, or would like to be a guest on an upcoming episode of this podcast, please reach out to us at [email protected].