Researchers at the University of Colorado School of Medicine said millions of people get a runny nose and have difficulty breathing without an allergic attack or infection.
While many people call it the sniffles, scientists refer to it as "non-allergic rhinitis."
Although it is common, researchers had, until now, not figured out why this happens - suspects include air pollution, strong emotions, and even spicy food.
The researchers led by Thomas Finger found cells lining the noses of mice that may be key to understanding the runny nose.
These cells - called solitary chemosensory cells (SCCs) - detect potential irritants and pass along the alert to pain-sensing nerve terminals.
The nerves then release a substance that triggers the body's defenses, called an inflammatory response. The result - among other things, a runny nose and difficulty breathing.
"Understanding how this works can help researchers try to figure out how to prevent this response," Finger said.
"What if we could deaden the pathway that the body takes to fight off an attack that, in this case, is not really threatening" he said.
It's not yet certain that the process is identical in humans, Finger said.
But if it is, and if some people are responding to substances or smells that appear to be a threat but actually are benign, then additional research could find a way to help millions of people to, literally, breathe easier, he said.
The study is published in the Proceedings of the National Academy of Sciences.