Something lighter, like snot.

My allergies may actually be killing me. M. Night Shyamalan released a movie called The Happening where plants basically killed nearly everyone in the world. That movie is real, only instead of going after everyone in the world based on the concentration of people, the plants seem to be targeting those cursed with the genetic deficiency that is allergies. Instead of the victims going crazy and committing suicide, we just drown in snot.