How Do Sniffer Dogs Detect Scents?

A dog's nose has roughly 100 to 300 million olfactory receptors, compared with about 5 to 6 million in humans. When a dog sniffs, some air goes to a special area at the back of the nose used only for smelling, rather than all passing to the lungs. Slits at the side of the nostrils let exhaled air out without disturbing incoming scents. The portion of a dog's brain devoted to analysing smells is proportionally much larger than ours. Trained dogs can detect explosives, drugs, missing people and even some diseases at extremely low concentrations.