Did you know that dogs can use their cold, wet
(and cute!) noses to sense sources of heat and thermal radiation?
That discovery, via a 2020 study from Sweden that challenged dogs to choose between a warm and cool object across a room, makes them only the second mammal known to possess that superpower. (The other is a vampire bat.)
1. Dogs' sense of smell is between 10,000 and 100,000 times as potent as humans’. This power comes in part from the up to 300 million olfactory receptors dogs carry around in their noses, compared to our mere 6 million. And the part of the canine brain that is dedicated to smells is 40 times larger than ours, proportionally speaking.
2. Dogs can smell continuously, even while they’re breathing in and out. In contrast, when a human smells a scent (sniffs a rose, for example) we inhale that odor and breathe in oxygen through the same passage. But if a dog smells the same flower, air “splits into two different flow paths, one for olfaction and one for respiration," Brent Craven, a Pennsylvania State University bioengineer who has modeled canine olfaction anatomy using high-resolution MRIs.
Craven and his colleagues found that a portion of the air dogs inhale gets ushered into a specialized area at the back of the canine nose reserved for odor detection, while the rest of it continues rushing toward the lungs. And when dogs exhale, that air departs through nose slits in a unique aerodynamic pattern that also guides new air in, creating a cycle of breath that continuously supplies the in-house laboratory in the back of the canine nose with new material. In one study from the University of Oslo, a dog on a hunt sniffed continuously for a full 40 seconds, across 30 respiratory cycles!
3. Dogs can wiggle their nostrils independently, which helps them figure out which direction a scent is coming from. Humans can only wiggle their nostrils simultaneously. (Try it. We’ll wait.)
4. Dogs are great at interpreting all the information coming in through their noses in fine detail. In her book “Inside of a Dog,” canine cognition researcher Alexandra Horowitz writes that humans might taste a teaspoon of sugar added to a cup of coffee. But a dog could detect the same teaspoon of sugar in a million gallons of water—enough to fill two Olympic-sized pools.
And to take the sugar metaphor further, “if we humans walk into a bakery, we can say, ‘someone’s baking a pie in here. A dog would walk in and say, ‘Oh, someone’s baking a pie in here, and it has apples, and butter, and cinnamon, and nutmeg.”
How does a dog’s nose work?
While humans have about five million olfactory receptors in their noses, dogs are said to have around 300 million. Dogs also have what’s been called the “second nose.” It’s the vomeronasal organ—alternatively known as Jacobson’s organ. Located in the nasal cavity near the roof of the mouth, and wired to a whole other part of a dog’s brain than the rest of the nose, this amazing organ allows dogs to detect specific compounds. Adult dogs use this piece of gear to detect pheromones and potential mates, among other things, and puppies can use it to find the source of mother’s milk.
With all those olfactory cells and the vomeronasal organ going for them, dogs don’t just smell more things than we do; they perceive and process the world differently. While dogs’ brains are smaller than ours (generally), the area in their brain that’s devoted to smell is 40 times larger than in humans.
Specialized cells called olfactory neurons are used to detect odors.
The structure of the nose is the secret to its amazing ability to detect, and understand, smells. A dog’s nasal cavity is divided into two separate chambers and opens into two nostrils, or nares, that can wiggle independently and that can take in smells separately. As a dog sniffs, particles and compounds are trapped in the nasal cavity by mucus while scent receptors process them. Scent particles are also trapped on the moist exterior of the nose. Some of the inhaled air goes to olfactory analysis and some of it goes to the lungs so your dog can breathe! As a dog exhales, new odors enter the nose through the slits in their nose, to keep a steady stream of odors flowing.
Sniffing out disease
Studies, and anecdote, have shown that dogs can use their amazing noses to detect the presence of diseases, including cancer. The first recorded case of canine cancer detection dates back to 1989, when two British dermatologists reported that a dog was persistently sniffing a spot on their owner’s thigh, which, upon examination, turned out to be a malignant melanoma. In another story, a dog “insisted” that a specific area of skin—already pronounced melanoma-free by doctors—was still cancerous. Upon biopsy-ing that area, physicians found the dog was right; the spot still contained cancerous cells.
In the meantime, service dogs rely on their acute sense of smell to detect health issues in their human before an incident happens. Service dogs can be trained to smell an epileptic seizure about 45 minutes before it happens, and some dogs can warn diabetes sufferers about an imminent hypoglycemic attack.