Dogs Have an Amazing Sense Of Smell

close up of dog noseLet’s begin by trying to understand just how sensitive a dog’s nose is.

Think of humans who rely on their “noses” for their livelihoods – perfumers, chefs, and wine makers, for example. Let’s put Sherlock Holmes in, too – someone able to “sniff” out the tiniest molecules of whatever poison lingered in the room or on the deceased’s body in order to find the culprit (at least according to Sir Arthur Conan Doyle). Now let’s multiply the extraordinary abilities of all these maestros by 1,000, 10,000, or even 100,000 times in order to find the starting point for our discussion of the dog’s sense of smell!

While the total size of a dog’s brain is approximately 1/10th the size of the human brain, the portion devoted to smell is about 40 times larger than ours.

The visual cortex is the largest part of the human brain – this is why we tend to analyze the world around us using visual clues (think of the saying, “a picture is worth a thousand words”). Dogs, on the other hand, analyze their world using scent. While a human being has approximately 5 million scent receptors in his nose, a tiny dachshund has 125 million, and a bloodhound (lovingly referred to as a “nose attached to a dog”) has 300 million!

The anatomy of a dog’s nose

anatomy of dog's noseThe dog’s nose has interior bony, scroll-shaped plates called turbinates over which air passes, as well as a thick, spongy membrane which contains most of the scent-detecting cells, as well as the nerves that transport the information to the brain for decoding. In human beings, this membrane is approximately the size of a postage stamp. In our canine friends, however, this area is roughly the size of an 8 ½” x 11” piece of paper.

Dogs also have another scent receptor, located inside the nasal cavity and opening into the upper part of her mouth, called Jacobson’s Organ, used to detect pheromones. It is hypothesized that a dog will combine all scent information in order to determine fear, breeding potential, and in newborn dogs, the scent of her mother, her mother’s milk and teat. As puppies are blind at birth, their abilities in the wild to differentiate scents were essential to their evolutionary survival.

close up of dog's noseWhy a dog’s nose is cool and moist

No, it’s not because it works to shock you out of bed on a sleepy Sunday morning!

One of the sources of a dog’s exceptional ability to smell is her wet snout. The moist, leathery surface of the snout acts like Velcro®, catching even the tiniest molecules of scents, and dissolving them so her internal smell receptor cells can analyze them properly. To keep her nose wet, a dog must produce a constant supply of mucus through her nasal cavities. Scientists estimate that an average dog produces a pint of this mucus every day. A trained scent dog may lick her nose sometimes, in order to assure that the microscopic bits of smell adhere well, giving her a chance to discern the required smell from all others around her.

Other physical traits contribute to a dog’s ability to discern smell

A dog’s physical make-up helps her discern scent, too. For example, a bloodhound, the breed of dog blood hound tracking with the most advanced sense of smell, has loose, wrinkled skin around her face which helps trap scent particles; and long, drooping ears that drag on the ground, collecting odours and brushing them into her nostrils. Her short legs position the bloodhound close to the ground, and the dog’s muscular shoulders enable her to retain that “on the trail” position for hundreds of miles. A tracking dog can trail an individual’s scent through densely populated areas, shopping centres, and city streets for hundreds of miles and for several days. Her “nose” is such an accurate tool that if the tracked owner of the scent is alleged to have perpetrated a crime, the dog’s identification of that scent is admissible as evidence in a court of law!

While we tend to code smells as “chocolate cake” or “bread”, our canine friends remember complex formulae, like “flour, cocoa, butter, baking soda, oil, etc.” (and even the specific type of flour and oil). Perhaps the next great game show could be “Iron Nose”, in which a world-class chef takes on a trained dog to see who can best determine individual ingredients in a dish!

bloodhound tracking dog in woodsSelecting and training scent dogs

Puppies are selected from their litters based on their desire to work, play, and please their owners. Trainers look for “nose-driven” dogs with lots of energy.

Dogs selected for scent training must be well-adjusted and socialized, as they will often be required to work around lots of people, and sometimes around people in states of shock and terror. The dogs must be healthy, and have a lot of stamina, as they may be required to work long hours and in very difficult and dangerous conditions.

Selected puppies must first receive obedience training – in order to become “sniffers” they must understand and obey voice commands.

Training initially takes the form of play, with rewards given for correct responses. In these initial stages, the trainer begins to understand and “read” cues given by the dog – a look, a cock of the head, a particular bark or sound – whatever small indication the dog offers to demonstrate her understanding of what is required of her. Dogs and trainers must learn to read and respond to each other’s cues, and this part of the training takes time and talent on both sides.

After this initial training, the dogs will learn to become “specialists” in their fields. They will work to develop and use their incredible abilities to discern and differentiate smells, as well as nurture their extraordinary desire to help their human trainers and handlers.

It’s important to note that sometimes we humans forget to allow our pets to be animals, and treat our dogs like babies and children. Dogs can gradually lose their keen senses of smell and depend more on their sense of sight. Very often these pets will become anxious and nervous; biters and barkers; and will require canine rehabilitation in order to revert to their “sniffing” ways. Even if your dog has no plans to become Canine Columbo, it’s important to allow her to rely on her sense of smell daily, and just “be a dog”.

Search and rescue dogs

Most of us have seen these brave dogs on the television news, arriving at a disaster scene, sniffing the air and ground, jumping through rubble, hoping to find living victims. German Shepherds, Border Collies, and Labrador Retrievers are some of the breeds well suited to this type of work. These dogs are so keen to find living victims that they have been known to become depressed or suffer from Post Traumatic Stress Disorder when their searches yielded only deceased bodies.

bloodhound tracking dog in woodsHow does a tracker dog decide in which direction a trail goes?

Breeds such as Bloodhounds and Dobermans are trained to discern and differentiate between scents in order to track only one, perhaps a missing child or an escaped convict. These dogs begin their detective work by sniffing an object with the required scent, (perhaps an article of clothing), first using frequent and rapid intakes of air, creating an “odour image” of exactly what scent to look for. This is followed by several longer sniffs, used to differentiate between any conflicting smells in the area, allowing the dog to decide which scent is the right one. Once the required scent is located, the dog will keep her nose to the ground, following the scent until she either discovers its owner or loses the trail.

Imagine your normal walk – each stride more or less one yard apart, each footprint taking only a second or two to make. While you’re walking, you are constantly shedding dead skin and assorted tiny organic particles with your “scent” on them. You may brush against a tree or bush, or stop on the sidewalk to wait for the traffic light to change.

The tracking dog searches the air and ground for concentrations of these scent markers, and then heads off in that direction. If she has chosen the wrong direction, she will stop suddenly, turn abruptly, and correct herself within a few sniffs! Even though the footsteps were taken mere seconds apart, the dog can tell the difference in the age of the scent, and will follow the fresher scent, thus knowing which direction to go.

The ideal conditions for a tracking dog are cool weather, no rain, a little wind, early morning or evening; and a trail on vegetation that is not too dense, and which has been undisturbed since the scent was recently laid. In these ideal conditions, a talented dog can track someone she has never met for hundreds of miles, and for up to 2 weeks, using only her nose as a compass!

Some dogs can track in pretty terrible conditions, too – on concrete, through rugged terrain, in strong winds and/or rain, in very hot temperatures, through cities filled with people, animals, traffic, and pollution. These conditions disperse and/or dilute the scent, and the tracker dog will compensate by sometimes leaving the direct trail, and sniffing the “sidelines” – gutters, light standards, fences, the grass or plants next to a sidewalk or path, even the crevices between sidewalk sections – to find the smallest concentrations of the scent in order to stay on the trail. A tracking dog of this caliber must combine instinct, learned behaviour, and an unwavering desire to serve and please her master. Whether this is “thinking” as we humans understand it, I don’t know – it certainly is intelligence, dedication, loyalty, and devotion, and is just plain amazing!

Police dogs

Border patrol dogs are trained to sniff out contraband on people and in luggage.

Cadaver dogs are trained to find corpses, even those which have been buried or submerged, as well as body parts, aiding detectives in crime scene investigation.

A bomb detection dog is trained to sniff out and alert her trainer to the location of individual components used to make a bomb, without ever disturbing the surrounding area; thereby avoiding the risk of detonating the device and causing injury or death to tactical teams or human hostages.

A dog trained to detect arson is brought to a fire scene, where the smell of smoke can be so intense that a human cannot discern any individual smell. These dogs can find traces of accelerants, such as kerosene or gasoline, aiding firefighters and police officers gain valuable time determining the origin of a fire.

Doctor Fido on call

Perhaps some of the most interesting research on a canine’s incredible sense of smell is being done in the areas of medical-assist dogs.

bomb sniffing dog with airport luggageSeizure alert dogs

A seizure alert dog has the ability to warn her owner before an epileptic seizure is about to occur – sometimes minutes before, and sometimes hours before. This allows the individual to take medication to prevent the seizure, or to seek a safe location if the seizure is imminent. These dogs can also be trained to stay with their owners during the seizure to protect them, or even to press an emergency device rigged to generate a 911 telephone call for help.

Cancer-sniffing dogs

Dogs are being trained to detect lung, breast, and other forms of cancer in humans with an accuracy rate equal to or better than multi-million dollar hospital scanners, and often before tumours are visible or palpable.

During their training, dogs are taught to pick out a specific type of cancer from samples of human urine or breath – and have an accuracy rate of between 70-90%. Researchers are not yet sure what the dogs smell – in lung cancer, for example, volatile organic compounds are released into the patient’s breath (the human breath contains approximately 4,000 different compounds), and it is hypothesized that the dog smells the minute changes in these compounds at the onset of the cancer. Detecting cancer at this very early stage obviously gives the patient the best opportunity to successfully treat the disease.

Dogs trained for disease detection can work in areas of the world where medical care is not available on a wide scale, whether due to impoverished living conditions, disaster situations, or remoteness or isolation of the population.

close up of dog noseRather than using dogs to replace machinery for detection, the hope is to eventually understand and identify what smell or smells are associated with the disease’s onset, and create a machine, a “mechanized chemical nose” if you will, for early detection.

While it may not be feasible to have canines on call at every clinic or medical facility, their abilities in detecting diseases such as cancer very early on may be the next quantum leap in the medical treatment of catastrophic illness. When researchers understand what the dog smells, perhaps costly, painful, and debilitating biopsies may become relics of the past; treatments delivered faster and more accurately; and recovery and cure rates rise dramatically.