Olfaction[source needed], also known as smelling, was a method of detecting chemicals. The quality detected was called an odour.
Different types of creatures used different organs to smell; humans used the lining of their noses, insects used their antennae and Myxilinic frost-worms smelled from above the central mouth. (PROSE: The Colour of Darkness) Though their olfactory system was similar to a human's, the Gallifreyans could do a chemical analysis of the air using their sense of smell. (PROSE: Doctor Who and the Carnival of Monsters)
In many species, like humans, the olfactory system used the same parts of the brain as memory and emotion. This was a weakness that the Dreamspinner, Shas-Raklat, exploited by changing the Karagulan's perception of events in order to abduct their children for spare sensory parts. (PROSE: The Colour of Darkness)
Pungent smells could indicate poison or toxicity. (PROSE: Wish You Were Here) Some species, like Raxacoricofallapatorians or the Ameteli, could be identified by their distinct smell signatures, like bodily gasses or calcium decay. (TV: World War Three, COMIC: Love is in the Air)