How Do Dogs Smell Things We Can’t?

How-Come. net — How do dogs smell things we can’t? asks Olivia Minogue, a student in Sayville, NY.

Sniff sniff sniff. You can actually see a dog’s nose hard at work, picking up a scent wafting through the air, following the invisible trail a rabbit left in the yard, or investigating your pants leg for evidence of a secret meeting with a cat.

No one knows for sure how much more scent-sensitive dogs are than humans: A thousand times? Ten thousand? But what is known is that a dog’s nose has many more odor receptors, and an olfactory (smell) center that takes up much more room in the brain.

Human beings have about 5 million odor receptors, while dogs, depending on the breed, may have more than 220 million. The small human nose devotes only a postage stamp-sized area to odor receptors. The average dog nose has a mucous-y scent receptor area which, if spread out, would cover a Kleenex tissue. A dog’s nose—moist on the outside, as well as the inside—acts as a magnet to scent molecules in the air and on the ground.

Sniffing—a string of quick inhales and exhales—helps a dog rapidly identify a scent. Each deliberate sniff widens the dog’s nostrils, allowing him to pull in more scent-laden air. According to researchers, a sniff also temporarily straightens the dog’s nasal cavity, allowing odor molecules to proceed directly to receptors deeper in the nose. The contact between molecules and receptors generates nerve impulses, which travel along the olfactory nerves to the brain’s huge smell center. Presto: Scent decoded.

(Meanwhile, Jacobson’s organ, a special chamber above the roof of a dog’s mouth, has its own scent receptors. These transmit nerve impulses to the brain’s hypothalamus, an area associated with social and mating behavior.)

The average dog’s ability to detect a few scent molecules in a trillion others has created a whole industry built on canine noses. Dogs sniff for hidden drugs in cars and planes, follow the trails of hikers missing in the woods, and find the remains of people in the rubble left behind by earthquakes and bombings. Now, scientists are testing the ability of dogs to detect the distinctive smell markers of various cancers.