Dog Superpowers: SMELL. Dog smell sense, a highly developed sense

Dogs are special in many ways. Today we will talk about some interesting facts about the terrific dog smell sense.

We will cover in this article:

Great smellers vs average smellers

What is the sense of smell?

What makes a dog smell sense superior? Dog vs human smell

What scent detection tasks do dogs work at?

What do dogs use their smell sense for (in daily dog life)?

How do dogs leave marks?

Dog communication with other dogs: the direct way

How does dog smell sense get into action during breeding?

What dog breeds are best at smelling?

What smells do dogs hate?

Great smellers vs average smellers

We all know dogs have a highly accurate capacity to perceive odors (chemical molecules floating in the air) with their well-endowed noses. Why is this sense of smell more developed in dogs than in other animals? As in dogs, other animals share a super sense of smell. All animals with this gift are classified as macrosmatic animals. This group of animals includes rodents (like hamsters, mice, and rats), cats, marsupials (like kangaroos), and rabbits.

We humans, together with other animals like cows and horses unfortunately don’t have such a perfect sense of smell. For that reason, we are classified as microsmatics, which means our dogs will beat us quite easily at perceiving the world through smell. Indeed, dogs have an olfactory sensitivity 10,000 to 100,000 times higher than humans!
Although human olfaction is not as good as that of a dog, surprisingly, we humans are able to recognize other humans or even members of another species (like our own dog, for instance) through the sense of smell. This may probably have to do with the more than 20.000 we have shared paths with our dog friends.
Quick note: we are not as accurate to tell apart the smell of our own cats from the smell of other cats.

What is the sense of smell?

The sense of smell is based on the recognition of airborne molecules called odorants. An inner, backend part of the nose is encharged of perceiving chemicals dissolved in the air surrounding us. Dogs are very efficient at doing this. The main reason for this is that their anatomy is better suited for this task (and their anatomy comes from thousands of years of evolution from wolves to their domestic equivalents).
For a dog (or any mammal) to perceive an odor, for instance, the smell of another dog, the chemical molecule corresponding to the specific odor (called an “odorant”) has to travel inside the nose to the very back-end, an area of mucosa specialized in the olfactory function. This area contains tiny hair-like projections with olfactory receptors. When the odorant gets dissolved in the mucus covering the olfactory mucosa and contacts the olfactory receptors, they match in a lock and key fashion, and in that precise moment, the receptors elicit an electrical signal (nerve impulse) that travels to the brain for the dog to become conscious of the odor and further processing (more on this below).

The exact place where this signal arrives is the dog brain cortex at the level of the sides – bottom of the head. Several neurons participate relaying this signal to this final destination and also connect to other areas of the brain (in less than a second) to elicit responses like emotions or behaviors typical of dogs. Being a macrosmatic species, these smell nervous pathways in the dog are very sophisticated (no surprise, they inherited them from their evolutionary cousins, the wolves, which hunt in the wild and rely on smell cues to survive).

Because of this high specialization for smelling dogs can detect a chemical (odorant) in the air in a concentration as low as one ppt (one part per trillion! = 1 part in 1,000,000,000,000 parts!!), which is equivalent to finding 1 needle in a million tons of hay or a drop of a given substance in 20 Olympic-size swimming pools. Equipped with this potent feature, dogs can do quite amazing things.

What makes a dog smell sense superior? Dog vs human smell

Here is a list of some of the natural equipment dogs bear to efficiently smell, compared to a microsmatic species like us humans:

• Larger nasal cavity size
• Dog exclusive airflow patterns generated by sniffing (short, sharp breaths).
• A 30-times wider area of the olfactory mucosa in their nose
• Near 30% more olfactory receptors ready to start a nervous signal from odorants in their olfactory mucosa
• Much bigger regions of the brain dedicated to olfaction (they are really big when comparing dogs vs humans!)

What scent detection tasks do dogs work at?

We all know dogs can be used, after special training, to detect hidden things through their sense of smell. Some of these tasks include:

• Explosive detection
• Drug detection
• Trailing humans for search and rescue
• Trailing human corpses or remains (from natural disasters or crimes)
• Tracking animals for hunting and conservation

Training is based on exposing the dogs to the smell of specific odorants and making Pavlov-like associations with playing and other positive-pleasant reinforcements (contrary to popular belief, dogs are not stoned or high while getting trained for drug detection, or punished, in general, for this kind of training).
Taking things a little bit further, dogs have such a powerful sense of smell that they can accurately “tell” if a human being is suffering from cancer or even infectious disease.
When a person is sick, his body biochemistry changes and tiny molecules will be released that dogs can detect through their nose. When we are not feeling well, our pets will know something is wrong (dogs can also detect adrenaline, the hormone of fear, and potentially attack intruders who are in stress of fear of getting caught). Dogs can be trained to sniff urine from a patient and smell disease-related molecules. This opens possibilities for dogs to help doctors diagnose diseases (believe it or not, like Covid-19).

Some dogs that excel at odorant detection can be cloned in an effort to obtain highly efficient working dogs. There are current techniques to do this that will safely produce totally healthy dog clones. This potentially avoids having to find families for the dogs that do not pass the training or even be sent to shelters.

What dogs use their smell sense for (in daily dog life)?

Dogs use their sense of smell to explore the world around them. In a sense, dogs see in a world of odors! They literally build a “smell world” inside their heads. Dogs smell other dogs, other animals, and humans and these perceptions and interactions produce smell maps of their surroundings and memories on their brains that help them successfully interact socially, mark their territories, recognize friends or rival dogs and locate food sources.

Odors tend to persist in the environment providing opportunities for dogs to communicate. Communication through odors may come in the form of cues that other dogs leave as scent signals without the need for physical or temporal proximity (a dog might have left an odor mark two days ago and currently be far away from that spot).
Odor communication among dogs can be unconscious and emotion-driven. Male dogs get crazy about a bitch in heat that lives blocks away (more about this below). It is amazing how dogs can detect the emotions of other dogs and even from humans.
Dogs leave marks on the environment for other dogs to smell through these “formats”:

• Urine
• Feces
• Secretions from glands

Inspection of these signals can be direct (on the other dog’s body) or indirect (by smelling the odor “mark” on the environment).
Let’s examine both ways of communication in dogs.

How dogs leave marks?

Urine can also be an effective means for dogs to scent-mark. Urine spots will be investigated to check whether the dog that left them is a potential threat or a handsome partner to mate with.
Feces also count for dog communication. While eliminating, feces press on glands located at the sides of the anus, called anal sacs. These glands produce odor substances that integrate into feces and remain on the ground for a long time so that other dogs will find and smell them. Feces will elicit similar responses as urine for the recognition of other dogs.

Odor skin glands produce secretions that also serve the purpose of communication. Odor producing glands are localized in specific regions of the dog’s body:

• Corner of the mouth
• Ear pinnae (outer ear)
• Prepuce
• Vagina
• Anal sacs

An interesting example of how dogs leave scent marks produced by special skin glands is when dogs scratch the ground with their paws, leaving chemical signals produced by glands between their fingers (interdigital glands).

When dogs roll on the ground what they are also leaving scent marks.
When dogs used to be wolves, this behavior allowed them to get impregnated with the odor of potential prey that passed by that spot recently. This information would brief the rest of the pack on prey size, location, or health status (a sick or weak prey would be easier to be hunted than a healthy one).
Modern dogs don’t need to go out in the wild to get food but they somehow remember who they really are and even today, they keep rolling on the ground! When we bath our dogs, they tend not to like the scents of shampoos and dog soaps, and if given the chance, they will roll on the grass to try to get rid of it! … apart from getting dry.

Dog communication with other dogs: the direct way

You may have seen how dogs greet each other when they meet. Greeting behavior in dogs involves olfactory investigation (aka sniffing).
Some areas of the body are more frequently subject of this sniffing investigation:

• Face
• Neck
• Inguinal (groin)
• Perineal (perianal)

How does dog smell sense get into action during breeding?

When female dogs are in heat (the only time during the sexual cycle domestic females accept the male for mating), they release odor signals, mostly through urine and vaginal secretions. Male dogs pick up these cues through their noses and become sexually aroused. They will respond strongly to these signals and will do whatever is in their hands (paws?) to escape, go down the street, fight other dogs, or whatever it takes to mate. As much “animal” as this may sound, that is the way dogs have behaved since the times they used to be wolves.
Male dogs will be very emotion-driven during this very short period of heat in females (just 9 days on average, once or twice per year). Due to this limited time for breeding, dog nature must act fast, and the sense of smell plays a big role.

When a female dog in heat urinates and a male dog later finds these urine spots, they will detect hormones and pheromones. One strong impulse of the dog will be to urinate on top of the female dog’s urine marks in an attempt to cover the original scent signal and in that way avoiding other competitors to “win the race” for breeding. On the dog’s mind, this is a form of exciting courtship (the female dog in heat might come back later and smell his “perfume” after all!)

What dog breeds are best at smelling?

The classical bloodhound is one of the best-suited dogs for scent discrimination, but other breeds are also quite good at it, like the ones on this list:

• Labrador retrievers
• German shepherd dogs
• Belgian shepherds
• Beagles

Interesting fact: The dogs in the list are not only good at detecting things through smelling but also have an excellent temperament that allows training for this task.
Drug detection dogs are so good at finding them, that they can find a hidden drug sample in about one minute in average. Among the best breeds presented above, German shepherds outstand at detecting drugs!
Some dog breeds are not so good for smelling tasks. When their smell capacity is tested, short-nosed breeds have the worst performances. Some people may worry that these breeds probably do not have an optimal experience while exploring their environment through smell compared to other dog breeds. Examples of these short-nosed breeds are:

• Cavalier King Charles spaniel
• Boston terrier
• Boxer
• American bulldog/boxer cross
• Bullmastiff
• English bulldog
• Pug

What smells do dogs hate?

Being so smell sensitive and relying on the sense of smell to scan the world, dogs can be distressed when facing strong or pungent odors. Think about a 20/20 person who is suddenly exposed to very strong light.

Several substances that dogs hate are also not so nice for us humans as well. Dogs are just more sensitive, and they will hate smells that are even strong for us humans.

In the end, many of these chemicals are diluted forms of what otherwise would be toxic substances (one of the purposes of the smelling sense is detecting toxic substances in potentially edible stuff).

The most agreed offending smell for dogs is citrus (orange, lemon, grapefruit).

Some other dog disliked smells come from hot peppers, spices, vinegar, ammonia (household cleaners in general), mothballs, alcohol, perfumes, and scented cosmetics. These substances may be used as deterrents or dog repellents (for instance, some people recommend spraying diluted citrus essential oil in places not allowed to dogs).

When comparing dog vs human senses of smell, some smells that we humans consider repulsive, will be acceptable or even likable by dogs. Having an ancient hunting instinct, some dogs will love to “cover” them with odors they believe will make them “invisible” to preys, like for instance garbage. This is not a general behavior in all dogs, but it does happen once in a while and may become a problem that should be dealt with with the help of our favorite Vet or animal behaviorist.

Please leave a comment about this article or if you are curious about any detail of the super smell sense in dogs.

In another posting, we will be talking about another dog superpower: <the hearing sense>