Smells so irritating they make you cough or gag may act on a single type of cell in the nose that senses caustic chemicals and warns the brain of potential danger, US researchers say.
Scientists thought such smells acted directly on nerve endings in the nose.
But this study in mice suggests special cells in the tip of the nose act as air quality control sensors that protect the body from harmful chemicals.
"You can imagine walking into an environment where there is a lot of irritating dust in the area. This would give you pause," says Professor Thomas Finger of the University of Colorado Denver, whose study appears in the Journal of Neurophysiology.
Finger says these chemosensory cells are found in most aquatic vertebrates, including sharks, bony fish and lampreys.
He thinks they are part of an ancient sensory system and they are probably present in all mammals.
"The current study is the first in mammals that has a clear idea of what these cells are responding to," Finger says.
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