The strongest sense for dogs is smell. In comparison to humans, dogs have almost 25 percent more scent receptors. Furthermore, the scent-detecting part of their brains is 40 larger than in human beings.
Just as many humans rely on their sense of sight to navigate, dogs rely on their sense of smell to understand and explore their surroundings. Dogs can smell scents about 100,000 times more acutely than humans, which makes them adept at many tasks, including hunting. Because of their acute and accurate sense of smell, some breeds of dog are being used for scent-based purposes in fields of medicine, such as detecting cancer. Since dogs can pick up scents that humans cannot detect, they are also valuable additions to law enforcement teams, where they help perform activities like smelling for drugs and weapons. To put dogs' keen sense of smell into perspective, dogs could see at 3,000 miles what people can see from one-third of a mile away, according to James Walker, who was formerly the director of the Sensory Research Institute at Florida State University. In scientific terms, that means dogs can smell odors at a scale of parts per trillion.
The Science of Canine Scent
Scientists attribute dogs' powerful sense of smell to their physical composition. Dogs can have millions of olfactory receptors in their noses. In comparison, humans have far fewer. The part of a dog's brain that processes scent is also 40 times bigger than the same part in humans. Dogs' noses also work differently from human noses. Humans smell and breathe through the same channel when they inhale, but the two compartments are separated in dogs. When dogs inhale, a piece of tissue in their nostrils folds over so that they inhale oxygen through one passageway and process scents in the other. In people, scents are processed in a small part of the nasal cavity. Essentially, the smells that humans pick up are transient and are released upon exhalation. In dogs, however, 12 percent of the air that is inhaled goes to the back of the nose while the rest of the air is released upon exhalation. The air with the scents filters through structures called turbinates. Turbinates filter and distinguish between odor molecules based on their size, then send electrical signals to the brain to have the scents analyzed and identified. Due to the physical structure of their noses, dogs can also determine what direction a scent is coming from in addition to identifying the scent itself.
Another factor that creates dogs' heightened sense of smell is the fact that they have a second olfactory system. In comparison, humans have just one. Dogs' second olfactory system contains the vomeronasal organ, which is also called the Jacobson's organ. This organ, which is located near the bottom of a dog's nasal passage, picks up the scent of pheromones, which are scents produced in animals that indicate their readiness to mate. Although scientists have made many discoveries on dogs' sense of smell, they continue to learn more about dogs' impressive scent capacities. Researchers are continuing to study the extent to which dogs use their sense of smell, and they are continuing to explore ways where dogs' scent powers can help humans make advances in the fields of science, medicine and more.