We see the world; dogs smell it. When your dog stops for ten seconds at a lamppost, they are reading who has passed by, when, and in what state. Their nose is a tool so fine that it is used to search for people, detect explosives, or find truffles. These are some facts that help to understand the extent of its reach.
A nose with many more receptors
The most cited figure is that a dog has up to some 300 million olfactory receptors, compared to about 5 or 6 million in humans. Pay attention to the "up to": the number changes greatly depending on the breed. Long-nosed dogs and hounds, such as the bloodhound, are at the high end; those with flat muzzles are well below.
- Surface area: a dog's olfactory mucosa occupies much more space than ours, thanks to bones coiled inside the snout that multiply the surface area.
- Brain: the area of the brain dedicated to processing odors is, proportionately, much larger than in humans. It is often said to be about 40 times larger.
- Sensitivity: estimates range from 10,000 to 100,000 times ours, depending on the scent and the method.
To get an idea, researcher Alexandra Horowitz explains it this way: if you notice a teaspoon of sugar in a coffee, a dog could notice it dissolved in about 3.8 million liters of water, something like one and a half Olympic swimming pools. It is an illustrative comparison, not an exact measurement, but it gives the scale.
How a dog smells
It is not just a matter of quantity. The design of the nose also helps.
- Two paths for air: when inhaling, part of the air goes to an area dedicated only to smell and the rest continues toward the lungs. We use the same path to breathe and smell.
- Exhale through the sides: the air exits through the side slits of the nose, so it does not "erase" the scent that is in front of them and even helps to pull in new air.
- Each nostril separately: dogs can distinguish which nostril a scent reaches them through, which helps them know which side a trail is coming from.
- A second system: the vomeronasal organ, in the palate, captures chemicals related to communication between dogs.
What they can detect
- Old trails: a good tracking dog can follow a person's path hours or even days later, depending on the terrain, wind, and humidity.
- Mixed odors: where we notice "the smell of stew," a dog can distinguish the ingredients separately.
- Changes in our body: in a 2022 study by Queen's University Belfast, four trained dogs distinguished sweat and breath samples from people before and after a stressful task with high accuracy.
- Diseases: there is research on dogs capable of detecting some types of cancer, drops in blood sugar in people with diabetes, or infections like COVID-19. The results are promising, but they vary between dogs and studies, and do not replace medical tests. Medical alert dogs are a support, not a diagnosis.
A unique nose print
The pattern of folds and ridges on each dog's nose is individual, like our fingerprints. It has been proposed to use it to identify dogs, although in practice what is used and required by law is the microchip.
Why sniffing tires and calms them
Sniffing activates the brain a lot. That is why a walk where the dog can sniff at their own pace leaves them calmer than a fast-paced walk of the same duration. Some ideas to take advantage of this:
- Leave time to sniff on walks, without pulling.
- Hide treats around the house and teach them to find them.
- Use snufflemats or fillable toys, which turn food into a little nose job.
- Try nosework with a trainer: it works for dogs of any age and size.
In our dog toys section you have snufflemats and interactive toys to give their nose something to do at home.