What We Know About the Nose of a Dog

The nose of a dog is no ordinary appendage. While you and I take on the world with our fingers and eyes, your pet’s natural reaction when encountering something interesting is to immediately sniff it. It is estimated that a dog’s nose can detect molecules in parts per trillion – that equates to about a half-teaspoon of sugar in an Olympic sized swimming pool.

In fact, compared to our primate schnoz, the dog’s nose is anatomically very different. This goes well beyond the fact that a “natural” dog’s muzzle (i.e., NOT the achondroplasia/ flat-face version present in some breeds) is much longer and obviously different in appearance. Their turbinates – little scrolls within the nasal passages – are far more ornate and complex than ours. This increases the surface area available for sensing molecules.

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A bloodhound’s nose is estimated to have up to 300 million scent receptors – more than 50 times that of a human’s.

When they inhale, the air moves in two directions. Most of it travels through the pharynx into the lungs to oxygenate the blood, just like us. But part of it moves to a complicated array of tissue at the front of the brain, lined with hundreds of thousands of sensors that filter and analyze with computer like speed. This is why dogs seem to take tiny sniffs rather than deep breaths when investigating new subjects. They also have a small organ located in the palate called the vomeronasal gland, which selectively detects pheromones that are specific to dogs.

Then when they breathe out, the air travels through the little slits at the side of the nostrils, rather than down the middle as it entered. This serves to steer new air – and new scent – into the center for further analysis. Bloodhounds and Bassett Hounds even use their long ears to “scoop” up scent and direct it toward their exquisitely sensitive noses.

But surely other animals have similar noses? Based on a genetic study published in the journal Genome Research, dogs only come in at number 9 for olfactory receptor genes – behind rats, possums, even certain frogs and sea turtles, and especially elephants! But what makes dogs unique is their ability – and more important, their willingness – to work with, be trained by, and communicate with humans. To place our interests above their own.

Putting this astonishing talent to work for humans has probably gone on for as long as dogs have been domesticated. Early on, of course, hunting for food was its most important use. Dogs are still used to locate prey for hunters, and this is at the root of selective breeding for large groups of dog breeds, ranging from terriers to pointers. Dogs can hunt truffles and root vegetables. They are used to find mold hiding in the walls of homes. They are tasked with locating survivors of avalanches and natural disasters, when time is critical. And it’s well known that dogs can sniff out the trail of a specific human in the wilderness, on a street or in a crowded city. More recently, they have enjoyed widespread utility in forensics, due to their incredible ability to sniff out illicit drugs or explosives in cars, suitcases, and lockers (or almost anywhere), to locate human remains buried under land or sea and to point a finger – er, nose – at evildoers.

Still, it was the innate behavior of dogs belonging to people with certain medical ailments that led behaviorists to recognize another important facet of the canine ability to sense trouble. People with epilepsy noticed their pet dogs becoming agitated before they (the humans) had seizures. This allowed the human time to find a safe place in anticipation of an episode. Likewise, dogs were able to alert diabetic patients when their blood sugar was getting too low. And in more recent news stories, dogs alerted on seemingly innocuous lumps that their owners had been ignoring, only to learn the lump was actually cancerous.

It was this abilityto detect cancer that led researchers to try to teach dogs to sniff out the COVID-19 virus in 2020. In the initial study, five Belgian Malinois – the most popular breed for police dogs – and a Jack Russell Terrier were tested on their ability to sniff out samples of sweat from humans infected with the novel coronavirus among samples from uninfected people. With scores ranging from 76 to 100% accuracy, these dogs proved it could be done. One Malinois and the Jack Russell earned the scores of 100%. They even detected infection in two of the “controls” – people who had tested negative – but when retested, both turned out to be carrying the virus, initially at levels too low to be detected the first time around. In other words, the dogs found the virus even before the lab test could! (Lab tests have gotten steadily better; it’s not clear whether this is still possible.)

What I and many researchers and observers find most fascinating about these studies is that no one knows what it is the dogs are identifying. This is true in most cases where service dogs have been trained to alert on such medical conditions as cancer, hypoglycemia or the pre-ictal phase of a seizure. We have no idea! Yet these dogs, sometimes without training, zero in on a barely existent level of “not normal” and have the confidence in their own detection to raise an alarm.

Because the presence of sniffer dogs in airports has become commonplace, COVID detection dogs are finding easy acceptance as a quick screening tool in airports around the world. Miraculous? Maybe not, but a useful weapon in our ongoing war against a pandemic that rocked our collective worlds in 2020.

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Though it is widely assumed that brachycephalic (i.e., flat-faced) dogs are less adept than the more natural style at discerning scent, this has been hard to prove. One study seemed to show that Pugs outperformed German Shepherds in a scent test, but this may have come down to motivation – the dogs were trained to sniff out tiny amounts of mineral oil in exchange for a food reward. The Greyhounds initially included in the study were mostly eliminated due to lack of interest and “failure to perform.”

Whether or not they are great at sniffing out food, Pugs and other brachycephalic dogs are often born with a condition called Stenotic Nares. This is one aspect of a wide-ranging medical condition called Brachycephalic Airway Syndrome, that drastically reduces their ability to breathe. A relatively minor surgery can sometimes be life-changing for affected dogs.

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A dog’s “noseprint” is as unique as a human fingerprint.

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The most common place for a dog to be bitten by a snake? You guessed it – the nose! This is due to their tendency to stick their faces into “intriguing” locations in pursuit of irresistible smells.

Dogs’ love of investigating the world with their noses leads to some interesting medical mishaps. They often snort in more than just air! “Foxtails” – stubborn grass awns – are a common foreign body found in dog noses here in the desert. If not caught and removed quickly, these barbs can prove fatal. Parasitic fly larvae such as Cuterebra sometimes set up housekeeping in a nostril, too!

Other parasites such as nasal mites can also invade and thrive in a dog’s nose or pharynx.

The complicated and rapidly growing lining of the inside of a dog’s nose makes it a target for tumor growth. Be alert for nose bleeds, oddly colored or persistent nasal discharge, or swelling of the nose or muzzle.

Dental disease, though it starts in the mouth, can lead to infection of the bones that line the nose, causing a hard-to-correct condition called Oronasal fistula.

Dogs with pale noses can easily be sunburned. You can protect it with lip balm that contains sunscreen, sunscreen made for infants or, ideally, sunscreen made specifically for dogs.

Dogs’ noses can be affected by age and climate, causing the skin over the nose to thicken, lose pigment, or develop scar tissue. These are benign changes that are typically symmetrical. But if you notice bleeding, discomfort or a change in one side that isn’t the same on the other side (asymmetry), ask your vet to check it out – it could be something more serious.

And finally: It has been estimated that a dog can recognize its human by scent alone from over a mile away!

Lillian Roberts, DVM, is the owner of Country Club Animal Clinic, which is located at 36869 Cook Street in Palm Desert. (760) 776-7555 countryclubdvm.com

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