What is the function of your dog's nose?

A dog's nose does more work than most owners realise. First, it filters and cleans the air your dog breathes, using the moist mucous membrane lining the nasal passages, and it warms and humidifies that air along the way. Smelling is the headline function, and dogs are remarkably good at it. Estimates put a dog's sense of smell at 10,000 to 100,000 times more sensitive than a human's, depending on the scent [1], letting them pick up faint ingredients and old traces we'd never notice.

The nose also handles communication. Dogs "read" scents left by other dogs, animals, and people to pick up on gender, health, and mood. It regulates body temperature too: dogs don't sweat the way humans do, so moisture evaporating from the nose helps them cool down. And it aids navigation, since dogs use scent to find their way home.

How does a dog's nose work?

A dog's nose is an incredibly powerful, complex organ. Dogs carry up to around 300 million olfactory receptors, compared with roughly 5 million in humans, and a dog's brain devotes a scent-processing region about 40 times larger, proportionally, than ours does [2]. Dogs can smell and breathe at the same time. Air entering the nose splits in two: one stream goes to the lungs, the other heads straight to the olfactory area [1].

They also carry a second, separate smelling organ tucked into the roof of the mouth: the vomeronasal (or Jacobson's) organ. It's specialised for picking up pheromones, the scent chemicals other animals leave behind [3]. That's what lets a dog work out another dog's sex and reproductive status just by sniffing.

Why do dogs sniff everything?

Sniffing is instinct, not a quirk. Dogs will sniff people, objects, other dogs, almost anything within reach. On a walk, that's how they gather information about who and what has passed through.

How good is a dog's nose?

A dog's nose can pick up odours in microscopic quantities. In controlled tests, trained dogs have detected scent compounds at concentrations down in the parts-per-trillion range, roughly like noticing a single drop of a substance stirred into an Olympic-sized swimming pool [4]. That's sensitive enough to pull a bowl of soup apart into its ingredients: the carrots, the herbs, the onions, each one distinct.

Dogs can also detect emotion. Fear and happiness both trigger chemical changes in human sweat and breath, and dogs pick up on them [5]. It's one of the most capable natural detection systems around.

What smells do dogs like?

Dogs gravitate toward certain smells. Chamomile and peppermint oil have a calming effect on many of them. Food smells, cheese and peanut butter especially, are an easy favourite. And they love the smell of their owner: it's familiar, and it's reassuring.

What smells do dogs not like?

Citrus and vinegar are a different story. Both are strong enough to put most dogs off, which is why some people use vinegar in the garden, and some trainers use it, to keep dogs out of certain spots. Cleaning products are worse: unpleasant to smell, and the fumes can actually irritate a dog's respiratory system. The same goes for chemical smells generally.

Predator scent works the same way. Wolf or fox urine reads as a danger signal, so dogs tend to avoid it.

Why is a dog's nose always wet?

A dog's nose stays wet because glands in the nasal tissue keep secreting moisture, and that moisture does real work. It captures odour molecules from the air and helps carry them to the olfactory receptors, part of the same airflow pattern that makes a dog's sense of smell so effective [1].

The wet nose also helps regulate temperature. Dogs don't sweat like we do, so evaporating moisture from the nose is one of their few built-in ways to cool off: useful on hot days, or after exercise.

On top of that, the mucus layer is protective. It forms a barrier against dust, dirt, and germs, cutting down the chance of anything harmful getting further into the body.

How long can a dog follow a scent trail?

Long after a scent seems gone to us, a dog can still follow it. Trained dogs can pick up trails that are days, sometimes weeks, old, and read a person's state along the way: stressed, scared, or calm.

Dog breeds with the best sense of smell

Dogs have the most powerful noses; these breeds have the best sense of smell of all:

• Bloodhound

The Bloodhound ranks number one. Their sense of smell is so precise that scent trails they've followed have been used as evidence in court.

• Basset Hound

A Basset Hound's nose is almost as good as a Bloodhound's, so this dog carries long ears and an excellent nose in equal measure.

• Beagle

Beagles are excellent tracking dogs. They're often used by customs services to detect drugs and contraband.

• German Shepherd

The German Shepherd is one of the most popular tracking dogs used by the police and the army. These dogs combine a fantastic nose with real intelligence.

• Labrador Retriever

Labradors have an exceptional sense of smell and are very often used as search and rescue dogs, or as detection dogs.

• Coonhound (Black and Tan/Redbone)

Coonhounds are hunting dogs. They're excellent trackers and can follow scent trails over long distances, even days later.

• Springer Spaniel

These dogs are often used in detection work for explosives and drugs. They have a fantastic nose.

Conclusion: What is the function of your dog's nose?

A dog's nose is an extraordinarily versatile organ. It detects scent at a level we can barely imagine, and it also handles communication, temperature regulation, and navigation. Thanks to that sense of smell, dogs track trails that are days or weeks old, pick up on human emotion, and pull apart the individual ingredients in a bowl of food. Breeds like the Bloodhound and the Beagle take it further still, which is exactly why they end up doing the tracking work most dogs never get asked to do.