Why do dogs smell after going outside

How Great Dogs Can Smell: The Anatomy of the Sense of Smell

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We humans perceive the first impression of our surroundings mainly through our eyesight.

Dogs, on the other hand, are Nasal animals.

The expert calls those animals in which a particularly well developed sense of smell is one of the predominant sense organs, occasionally also "Macrosmatic“.

It is quite obvious that with their fine noses dogs can perform unimaginable feats:

Dogs can not only sniff out our emotional states or simply a rubber ball in the undergrowth. They are trained as search dogs in all sorts of areas and on every walk they experience a world that remains hidden from us.

But why can dogs smell so good?

How does the sense of smell work in dogs?

The sense of smell is a fairly old invention in the animal kingdom.

It enables prey, predators and competitors to be scented. It allows an assessment of sources of danger, the finding of sexual partners and through territorial marks even communication with other individuals.

The olfactory performance of our dogs is particularly effective.

Have you ever thought about getting a sniffing rug for your dog?

Then take a look at the article on sniffing carpets for dogs.

We have been taking advantage of this for a long time and train dogs as sniffer dogs for all kinds of substances:

On our behalf, dogs look for cancer in tissue samples, mold, drugs, money, truffles, game, missing people or just lost items.

Special sniffer dogs accompany people with PTSD, diabetes, epilepsy and other diseases and warn their owners early on of any physical emergency.

On the other hand, we cannot always understand the importance of the sense of smell to the dog.

Without foresight to any possible restrictions, we simply breed the snout of some dog breeds because we think that's cute.

And sometimes we are annoyed or even disgusted when our dog sniffs the urine of a fellow for half an eternity and then takes a "taste test" with pleasure.

So: What makes the dog's sense of smell so special?

The structures that are involved in the sense of smell are much more sophisticated in dogs than in us.

This applies above all to the following aspects of the sense of smell:

The dog's nose

The nose in humans and dogs is already outwardly different:

Our nose is known to be a "skin-covered bump" in the front of the face through which we breathe in and out through the nostrils.

With dogs it sits leathery hairless nose at the tip of a more or less long snout. The doggy ones Nostrils are also narrowed to narrow slits on the outside.

This enables the dog to inhale through the front nostrils and exhale through the side nostrils. A skill we lack.

This prevents you from exhaling frontally forward while sniffing. Because that would blow away scent molecules that the dog actually wants to sniff out.

The two halves of the nose inside the nose are separated by a nasal septum, as is the case with us. In contrast to us, dogs are probably the most effective "Directional smell" in a position.

The The temperature and humidity of the dog's nose fluctuates throughout the day, with increasing age and also between different breeds of dogs.

The reason for this is not entirely clear. It is, however, an old wives' tale that a temporarily dry, warm nose is a cause for concern.

The moisture in the nose comes from gland secretions (for example, only sweat on the nose and paws). But dog saliva also covers the outside of the nose.

Because Dogs regularly lick their noses with their tongues. The nose of many dogs is particularly dry when they get up in the morning because dogs are less likely to lick their noses while they sleep.

Dogs don't just wet their noses with their tongues. With their tongue they absorb fragrances from the surface of the nose, which they can "taste" in the oral cavity.

And scent molecules from the environment stick particularly well to a damp dog's nose.

Each dog's nose has an individual pattern that is as unique as our fingerprint.

The anatomy of the nasal cavity in the dog

The cavity behind the nostrils is called Nasal cavity.

Mammals have bony lamellae in their nasal cavity, which are covered with mucous membrane.

These "Turbinates“Ensure a larger surface of the mucous membrane and structure the cavity of the nasal cavity in different levels.

In humans, these nasal conches are quite simply structured.

In the dog, on the other hand, the turbinates are very branched and fill almost the entire nasal cavity.

On the one hand, this results in the dog surface covered with mucous membrane again enlarged much more extremely and on the other hand, the air flow is much finer than ours.

These structures can be seen very clearly on the skulls of humans and dogs:

Dogs differentiate between breathing air and taster air

In dogs, there is a much clearer control of the inhaled air.

After inhaling, the air in the front area of ​​the snout is first in the winding corridors of the Respiratory mucosa moistened and warmed up.

Much of each breath is then passed through the lower part of the nasal cavity into the secondary airways directed.

About 10% of the volume of air sucked in is directed through a passage in the roof of the nose through a dead end street behind the upper area of ​​the nasal cavity, in which the Olfactory mucosathe dog is located (Craven et. al. 2010).

This area of olfactory perception in dogs is even separated from the pure respiratory part of the nasal cavity by a small bone process of the dog's skull.

This enables dogs to “settle” and accumulate odor particles here.

These Separation of the air flow inside the nose does not exist with us humans.

With us, the air we breathe is transported relatively directly through the nasal cavity.

And when you exhale, we blow the air back out through the nostrils in the same way. This breathing air slides over our comparatively puny olfactory mucous membrane in the roof of the nose. But with us, fragrances hardly have the opportunity to "sit down".

The breathing technique when sniffing

Dogs don't just smell better because their nose's anatomy is different from ours.

dogs sniff particularly effective.

Imagine you notice a strange smell somewhere in your apartment.

How do you react

You inhale several times in quick succession and try to locate the source of the smell.

When sniffing, you breathe through your nose particularly quickly and in spurts.

As a result, scent molecules accumulate on the surface of the olfactory mucous membrane with every breath. This increases the likelihood that these olfactory molecules will actually hit the receptor of an olfactory cell.

Dogs have perfected this breathing technique.

Your Sniff frequency is well above ours.

Healthy dogs can also widen their nostrils upwards when they inhale.

As a result, the breathing air reaches the olfactory mucosa quickly and in a targeted manner along the passage in the roof of the nose without having to take the winding path through the entire lamellar structure in the dog's snout.

Since the olfactory mucous membrane is also in a blindly ending dead end, the air lingers here longer and thus increases the enrichment of fragrances with each additional breath.

The olfactory mucosa

As already mentioned, a distinction can be made between the respiratory mucosa and the olfactory mucosa in the nasal cavity.

In the Respiratory mucosa there are almost no olfactory cells. Nevertheless, it fulfills many functions:

It cleans the air of dirt particles and pathogens with fine cilia, warms the cold air through effectively arranged blood vessels in the nasal entrance, secretes the secretion of the nasal mucus and humidifies the air.

In the Olfactory mucosa on the other hand, one finds the majority of the specialized olfactory cells. Only these sensory cells can recognize chemical scent molecules in the air we breathe.

The olfactory mucous membrane of a dog's nose is lined with many more olfactory cells than ours:

It is believed that humans are around 5 million of these olfactory receptor cells. This can be found almost exclusively in the roof of the nasal cavity on an area the size of a postage stamp.

Dogs, on the other hand, have about 300 million of these olfactory sensory cells.

(Such numbers are never very, very precise. Something like that is not counted by hand, but extrapolated on the basis of tissue samples.)

The olfactory mucosa in the dog is very heavily branched and when unfolded it would be roughly the size of a sheet of paper.

The size of the olfactory mucous membrane alone does not create a “good nose”.

Only the interplay of factors such as nasal anatomy, skilful air transport, large olfactory mucosa and high density of sensory cells allow the dog to use its sense of smell to the full.

Dogs not only smell more intensely or recognize odors from very few scent molecules.

Due to their much finer nose, they are also able to differentiate between individual smells much better.

The olfactory sense cells in the dog

The Olfactory cells lie embedded in the mucous membrane and stretch several small elongated processes (Cilia) through the mucus layer. The olfactory cells are attached to these cilia Receptorswith which they can bind to certain fragrance molecules.

The olfactory cells are at the same time Neurons. If enough identical olfactory molecules are recognized on the cilia of a certain olfactory cell, a electrical signal sent out into the olfactory brain.

There are many different Olfactory cell typesthat differ from each other by different receptors. Each type of receptor binds to different groups of fragrances.

This is what makes it possible to distinguish between different smells at all.

The genes that the blueprints for these receptors are based on make up a significant portion of the entire vertebrate genome.

Different vertebrates have olfactory receptors adapted to their respective way of life.

Dogs are not necessarily always superior to us here, they just smell different things than we do.

For example, we are better at assessing the degree of ripeness of fruits. Conversely, dogs also have some types of receptors that we lack (Quignon et. A. 2013).

The olfactory brain

The totality of the tissues that are involved in olfactory perception is called the olfactory brain.

The nerve fibers of the olfactory mucous membrane send their signals to the Olfactory bulb. This is a thickening at the front of the brain in which olfactory information are processed.

In humans, the olfactory bulb is only recognizable as a very slim structure at the front of the brain. For us, the sense of smell only plays a subordinate role in the perception of our environment.

In the case of dogs, however, this area makes one considerable proportion of the total brain volume and protrudes clearly forward over the endbrain towards the olfactory mucosa.

The information from the olfactory bulb is sent on to other areas of the brain via the so-called olfactory tract.

Only then does the conscious and subconscious perception of smells take place.

Nothing is known about how smelling feels for our four-legged friends. Do we think of his ball when he can smell it? Does a dog see a deer in its "inner eye" when it sniffs for traces of game?

How the dog experiences smells remains a mystery to us for the time being.

The Jacobson organ: dogs taste smells

Not only the dog owners know this well: The dog sniffs with pleasure in one place, maybe even licks his tongue over a blade of grass and suddenly starts chattering your teeth.

Owners of (would-be) hunting dogs are also familiar with the behavior when the dog smells prey in the undergrowth: it pulls its nose up, sniffs with its mouth open and sometimes even begins to smack the air.

This is obviously a kind of "Smell tasting“That we cannot understand with our sensory organs.

Because dogs have an organ that has been lost to us:

In addition to the olfactory mucous membrane deep inside the nose, vertebrates also have another organ with which they can perceive odorous substances: that Jacobson organ or Vomeronasal organ.

In humans, by the way, this small organ is considered stunted and functionless.

The Jacobson organ is embedded in the soft tissue to the side of the nasal septum and extends as a tubular indentation along the front length of the snout.

The air we breathe in the nose does not reach this organ directly.

Directly behind the incisors in the dog's skull, however, there are two openings in the palate, which are used instead the oral cavity is connected to the Jacobson organ becomes.

This is also the reason why dogs sniff with open mouths, chatter their teeth, sometimes smack the air or frequently lick their noses.

Because in this way they can transport fragrances to the roof of the mouth via the tongue.

As a result, the odor molecules reach the Jacobson organ and are checked there for interesting messages.

The Jacobson organ is not actually there to smell.

This particular organ will be mainly intraspecific Pheromones and signal substances recognized.

The Jacobson organ even has a nerve line separate from the olfactory mucosa. The signals from this organ are not only processed and “smelled” in the olfactory brain.

The information is sent directly to the areas of the brain that are attached to the Creation of emotions and the control of behavior are responsible.

When the Jacobson organ is activated, it can have a direct impact on our dog's behavior.

Dogs are not the only animals that use special behavior patterns such as the chattering of teeth to direct their breathing air specifically to the Jacobson organ.

Many animals “fleh” in a very spectacular way and the “licking” of reptiles also serves the same purpose.

How good do dogs smell?

Dogs have perfected the anatomical structures and air transport through the nasal cavity.

So much is clear: our dogs' sense of smell is highly effective and a lot more precise than ours. However, it is difficult to measure what and how good dogs smell.

For example, we cannot perceive with our senses who has walked down the same sidewalk in front of us. Dogs can recognize and even smell these invisible footprints of individual people, in which direction was gone (Thesen et. al. 1993).

A dog's olfactory test was used to observe how far you can get a Odor concentration can lower until two dogs trained on this odor began to guess when carrying out the search.

Here one came to the rough conclusion that at least the two investigated Dogs can smell an estimated 10,000-100,000 times more accurately than we can (Walker et. all. 2006).

Overall, however, there are only a few such behavioral observations that deal with the olfactory performance of different dog breeds.

The fascinating canine olfactory performance does not only include the detection of individual smells in vanishingly low concentrations.

Aspects such as the ability to differentiate between similar smells, to perceive many smells at the same time or to be able to taste pheromones from the air have hardly been researched.

And of course temporary factors such as the state of health, medication or simply the weather can also be current odor output influence (s. Jenkins et. al. 2018).

Every dog ​​owner knows that it is special from a dog's point of view To sniff a lot on wet days gives.

Of course, it also depends on what exactly you let the dog look for, whether the dog has already been trained for nose work or what breed the dog belongs to.

More recent studies therefore also deal with UDifferences in smell performance in different breeds of dogs.

On the one hand, there seems to be an accumulation of some genetic variants in the olfactory receptor genes in different dog breeds. The extent to which this actually influences the odor performance of individual groups of dogs is, however, questionable for the time being (Robin et. al. 2009).

In a behavior test in which dogs look Hunting dog breeds compared to other dog breeds, flat-nosed dog breeds, and wolves wolves and hunting dogs did the best (Polgár et. al. 2016).

A breeding selection for nasal performance does not seem to be just imaginary.

Brachycephalic breeds are clearly disadvantaged when it comes to sniffing.

Especially in flat-nosed dog breeds, the airways are often severely deformed and the nostrils narrowed to narrow slits. It can be assumed that this has an effect not only on stamina and freedom of breath, but also on the ability to smell.

The sense of smell is extremely important for dogs to be able to experience their environment. A dog that cannot or may not regularly sniff to its heart's content is a poor dog.

Finally, a great video (in the settings behind the small gear icon you will find useful German subtitles):

Categories Dog KnowledgeTags Sniffing