Dogs have an additional smelling apparatus that is not available to humans.
The scent discrimination ability of dogs appears to be prodigious when compared to that of humans. It has been estimated that the sensitivity of dogs to odors may be 1,000 times, or even 10,000 times, greater than that of people (depending upon the particular scent involved). Their scent detection and discrimination ability is so good that several airports are now using sniffer dogs to detect COVID-19 in arriving passengers.
Although all dogs have fine scent recognition abilities, their talents can be improved through selective breeding. The beagle, the basset, and the bloodhound are good examples of how sensitivity to odors is, at least partly, genetically determined. These dogs have been bred as specialists, with not only a special ability to detect and discriminate scents, but also with a passion to follow, track, and explore odors.
A dog’s nose has two functions—smelling and breathing.
According to Dr. Nappier, a canine’s nose has the ability to separate air. A portion goes directly to the olfactory sensing area (which distinguishes scents), while the other portion is dedicated to breathing.
How good is a dog’s nose?
The bony ridge inside of the dogs nose which contains the smell-detecting cells varies in size, depending upon the overall size of the dogs nose. Dogs with longer and wider noses have more of this surface available, while dogs with flat faces and short noses, like pugs or Pekingese, have a smaller surface area in this portion of the nose, and therefore simply dont have the room for as many scent-detecting cells. Typically, the dachshund has around 125 million smell receptor cells, while a fox terrier has 147 million and the German shepherd has about 225 million.
Some dogs, in particular the dogs that we call “scent hounds,” have noses that are designed to be very wide and deep in order to pack the largest number of odor analyzing cells into the available space—even if the dog itself is not very large. Thus the very scent-oriented beagle, who normally weighs in at only about 30 pounds, and stands only 13 inches at the shoulder, has the same 225 million scent receptors as the German shepherd dog, who is approximately twice his size at 75 pounds with a height of 24 inches. The bloodhound is the grand champion of scenting, at least in terms of the number of olfactory receptors. These big-nosed dogs check in with around 300 million scent receptors in their noses, the largest number in all of dogdom.
How do these numbers of scent-detecting cells in the dogs nose compare with those in humans? Human beings are not very smell-oriented, and one of the reasons for this is that we have noses that contain a paltry 5 million smell analyzing cells. This means that the average human being has a nose that contains only 2 percent of the number of odor analyzing cells that can be found in the nose of the little beagle.
But that huge number of olfactory receptors in dogs is far from the whole story. It seems that dogs may have a separate, second “nose.” Some dog owners have observed an ominous-looking bump on the roof of their dogs mouth, right in the middle and just behind the top two middle teeth. That bump is called the “incisive papilla” (papilla is just the word for bump, and this one is located near the incisor teeth). Some veterinarians report that when dog owners first see this, they often make a panicky veterinary appointment, dreading the worst. However, this bump has a precise function. In the middle of it, theres a hole that is a duct that communicates with the dogs Jacobson organ (also known as the vomeronasal organ). This is a separate olfactory system for analyzing scents.
The particular scents that Jacobsons organ is designed to detect are biological odorants, and most of these are pheromones. Pheromones evolved as a chemical means of communication between animals, usually of the same species. They are secreted from glands found in the genital/anal region and glands between the toes and around the mouth. That means that they are also found in the saliva and urine of dogs.
Some pheromones contain important sexual messages that indicate the reproductive status of the females: for instance, whether they are in the receptive portion of their cycle.
Alarm pheromones may be left behind by frightened dogs, and these trigger anxiety in other dogs. Thus, dogs in waiting rooms at the vet may pick up these pheromones and react in a stressful manner.
Recent research has shown that there are also pheromones that have a calming effect. When a mother dog gives birth, she releases special pheromones which are meant to comfort her puppies, and nowadays synthetic versions of these are often deliberately used since they appear to relieve anxiety even in adult dogs.
Some pheromones mark territory. When dogs scratch the ground after they have eliminated, they are releasing pheromones from their paw pads which can be detected by other dogs. Territory is also marked in dog urine, which explains why dogs are so obsessed with the act of marking and sniffing the marks of others. These pheromones convey a lot of information about other dogs in the area.