Updated: Mar 29
By Kaelie Breiter
How can a dog smell one tablespoon of sugar through a million gallons of water? Or one dirty sock in a pile of two million clean ones? Their sense of smell is 10,000 to 100,000 times better than people, and they can detect odors in parts per trillion. It is impressive and fascinates me whenever I look at my Australian Shepherd, Buddy, and my English Cream Retriever, Snowflake, sniffing constantly. I wondered why they sniff all the time, how their sense of smell works, and how their extraordinary noses may help in society, through law enforcement.
So why do dogs sniff all the time? Dogs have 300 million receptors in their nasal cavity compared to humans who have 10 million. While they communicate and interpret their surroundings with both their eyes and noses, they do so more with their noses since it is their main way of understanding the environment. Plus, smelling lowers their stress level and they truly enjoy it. When they are constantly sniffing everything on walks, they are finding out about the area, who lives there, who has passed by recently, and even what kind of mood the person is in; they are constantly processing information and interpreting the world to determine who and what is in it through their noses. Thus, this is why dogs sniff you when you meet them: they are seeing if you have a dog, or what you have just eaten, or what kind of person you are. They do not need to see us to identify us. Dogs are motivated by smell and want to get detailed information up close and personal. I have always wondered why Snowflake smells Buddy after he has been to the groomers. I know now that she does this because she uses her sense of smell to catch up on where he has been and who he has been with. Jokingly, in our family we say, “He is the same dog, why are you smelling his butt?”
So why is a dog’s sense of smell better than a human’s? How do their noses work? When a dog smells a scent and breathes it in, the inhaled air flow splits and goes into two distinct chambers: the olfactory area (sensory system used for smelling) and down into the pharynx and into the lungs. Less air goes to the olfactory area, which is filled with turbinates, a succession of short bony structures filled with scent detecting cells and nerves that carry sensory information to the brain. Turbinates work as a sifter (much like how a blue whale filters krill through their teeth) that causes the receptors in the olfactory system to connect with the brain (temporal lobe part) and recognize these odor molecules by their shape and dispatch electrical signals to the brain for analysis so it can classify each scent. The temporal lobe of the brain in dogs is responsible for analyzing smells 40 times larger than humans! People also have turbinates. Looking microscopically at these bony structures reveals a thick spongy membrane that is about the size of a postage stamp in humans but in dogs it is about the size of a piece of typing paper. So dogs obviously have a larger area for scent detecting cells and nerves to better analyze a particular smell. And they are able to increase the amount of scents they breath in because of the bigger membrane in their turbinates. The dog then breathes out through slits on the sides of their nose. This breathing process allows the dog to take in new scents while filtering out old ones. An important part of this swirling air allows the dog to sniff more continuously. Dogs can actually detect and identify which smells they inhaled through each nostril because the aerodynamic reach of their individual nostrils is smaller than the distance between the nostrils. Additionally, dogs can wiggle their nostrils independently! This allows them to determine the source of the enticing aroma and go back over the same scent to identify it better. Interestingly, I came across a study done at the University of Oslo with a hunting dog. While in search of game, it was observed holding its head into the wind and sniffing a continuous stream of air for 40 seconds, spanning at least 30 respiratory cycles. Amazing! But wait, dogs have more!
A second olfactory system?! In my research I found out dogs actually possess a second olfactory system consisting of a vomeronasal, or Jacobson’s organ, that humans do not possess. Jacobson’s organ is a paired supportive olfactory smelling organ located in the soft tissue of the nasal septum, just above the roof of the mouth (the hard palate). This organ zeroes in on the pheromones, the different chemicals that are released and produced by specific animals. The pheromone molecules that the organ detects—and their analysis by the brain—do not get mixed up with odor molecules or their analysis, because the organ has its own nerves leading to a part of the brain devoted entirely to interpreting its signals. These nerve cells respond to a range of substances that often have no odor at all. These particular nerve cells work to detect “undetectable” odors, much like a computer server. So essentially dogs are simultaneously running two separate olfactory systems in their nose and in their brain all the time. An extraordinary sensory organ indeed!
Dogs help law enforcement in many ways and are able to detect bombs, weapons, drugs, blood, body fluid, and are known to find missing people and locate dead bodies. In one case I investigated, Breston, a Belgian Malinois who works with the Cheektowaga Police Department in Cheektowaga, NY (a suburb of Buffalo), easily sniffed out a shipment of marijuana in heat-sealed bags, inside plastic-lined crates sealed with foam sealant, inside a closed storage garage. Breston found $3,400,000 worth of drugs and kept them off the streets. In addition to sensitivity, a dog's sense of smell is picky. It can discern a specific scent even when there are dozens of other scents around. Drug dealers have tried to fool drug-sniffing dogs by wrapping drugs in towels soaked with perfume, but the dogs always find the drugs. Most interesting to me are the cadaver dogs and how they find human remains with their powerful nose. They can sniff out dead human tissue that is 6 months old, bones that have been buried for 2 years, and body parts underwater. Unbelievable! I was curious as to how these noses are trained. In my research I found that the officer/handler and dog start by playing with a white towel. Then, the handler hides the towel for the dog to find. Eventually, the towel is sprinkled with black powder – for explosives training – or wrapped around pouches of marijuana – for drug detection, or smothered with dead body tissue for cadaver training. Now the dog is imprinted with this particular scent in his olfactory system, so the dog will detect it again if he comes across it on this crucial job.
A dog’s nose is truly an incredible sensory organ that deserves understanding. They have a sophisticated olfactory system that allows them to figure out the world around them. People have realized the value of a dog’s nose as evidence by its use in law enforcement. Interesting fact, experts estimate that a single search and rescue dog can accomplish the work of 20 to 30 humans! One more interesting new study has shown that dogs can use their highly evolved sense of smell to pick out blood samples from people with cancer with almost 97 percent accuracy. After researching this topic I am aware that the complexities of the dog’s nose gives them a window to the world outside, so I let Buddy and Snowflake sniff just a little longer on our walks.
How many more times better is a dog’s smell than humans?
10,000 to 100,000 times better.
Why do dogs sniff so much most of the time?
Dogs use their noses to figure out the world around them through different smells and odors so they can interpret what is happening. Their exceptional noses help them do this.
What is Jacobson’s organ?
Jacobson’s organ is a paired auxiliary olfactory smelling organ located in the soft tissue of the nasal septum, just above the roof of the mouth (the hard palate). This organ zeroes in on the pheromones, the different chemicals that are released and produced by specific animals. Jacobson’s organ has its own nerves leading to a part of the brain devoted entirely to interpreting its signals. These particular nerve cells work to detect “undetectable” odors.
How many humans would it take to accomplish what one search and rescue dog can do?
20 to 30 people!