A dog’s sense of smell is very different from a humans in many ways. First, dogs have about 300 million olfactory (smell) receptors compared to humans who have only about 6 million. Second, when a dog inhales, their nose separates air into two streams. One stream goes to their lungs and helps them breathe.
The second stream goes to olfactory sensors in the back of their nose cavity. In humans, when we inhale, the air we smell goes in and out with the air we breathe. In addition, the part of a dog’s brain that analyzes smells is about 40 times larger than a humans.