How Far Away Can a Dog Smell?

Working Noses

• Dogs are admired for their ability to sniff out trouble, which is why government agencies use them to search for explosives, drugs and other contraband. Buddy's ability to smell relies on many things, such as the weather, the presence of man-made scents such as perfumes and petrol, and distractions, such as freshly cut grass, which can overpower his nose. The breed of dog makes a difference, too. All of these influence the distance a dog can smell.

More Than Distance

• There's no set distance a dog can smell, though there are reports of dogs sniffing out things over significant distances. Nova noted a Seattle dog able to detect the scat of an orca whale from a mile away in the Puget Sound. The New York Times reported on dogs sniffing out wildlife scat from 33 feet. Although both reports are admirable, it's not the distance that Buddy can smell across that's so impressive; it's what he can smell that's remarkable. Consider this: if you walk by the bakery and enjoy the smell of fresh-baked cookies, your pup can detect the scent of each ingredient. We can detect a spoon of sugar in our cup of coffee, but Buddy can smell the same amount in a million gallons of water.

Dogs Smell Better Than People

• Buddy's sense of smell is much better than yours, perhaps as much as 100,000 times better. If you equated his sense of smell to vision, what you see at a third of a mile, he'd see at 3,000 miles away. Compared to your 5 million scent glands, Buddy has 125 million to 300 million scent glands. Your brain is quite a bit larger than Buddy's, but the part that controls his smelling ability is 40 times larger than yours.

Buddy's Amazing Nose

• Buddy's nose is built so he can sniff and breathe, which are two different things. When a dog inhales, air goes into two passages: one leads to the lungs for breathing and a second targets his olfactory sense. The air destined for smelling is filtered through turbinates -- scroll-like structures that separate odor molecules based on chemical properties. Olfactory receptors send information to the brain to analyze what Buddy's smelling. When he exhales, the spent air leaves his nose through side slits, actually helping new odors into his nose and allowing him to sniff almost continuously. Being able to move his nostrils independently also helps Buddy's ability by locating the source of a smell. The icing on the cake is his Jacobson's organ, at the bottom of his nasal passage, which picks up pheromones used in mating.

Using His Nose

• When Buddy greets a canine pal, his sniffing is more than a "Hello, how are you today?" He learns whether the pup is male or female, where he's been, what he's eaten and what he's touched. Of course, that's all useful for Buddy, but it doesn't end there. In addition to drug- and bomb-sniffing work, there's increasing evidence, anecdotal and scientific, about dogs' ability to sniff out illnesses. Anecdotal evidence includes numerous stories of detecting blood-sugar drops and epileptic seizures. The Pine Street Foundation released a 2006 study of some 12,000 trials in more than 160 patients where dogs correctly identified cancer samples by scent about 90 percent of the time.