All animals have a more developed sense than the rest. In the case of humans, we mainly depend on sight for our daily lives. However, in the case of dogs it is different. As human beings it is impossible for us to understand their sense of smell since we cannot understand the world through this sense as they do. Their sensory world is impressively different from ours, since they are animals capable of processing a lot of information through chemical messages.

It is the most developed sense they have, and this is due to the 300 million olfactory receptors they have. We, on the other hand, have 6 million, as well as a nasal tissue 30 times smaller than theirs.

But what does it mean that their main sense is smell?

Although it’s hard to imagine, a dog concentrates a large part of its brain energy on processing and interpreting smells. This means that they can orient themselves thanks to everything they smell, as well as detect what time of day it is, according to the concentration of particles in the air.

To give us an idea, a dog can smell 10,000 times better than us, or more.

Although their noses don't literally speak, they do communicate. With a simple sniff, a canine nose can interpret an entire story, wordlessly, using aminos and acids emitted by dogs as the basis for chemical communication.

Chemical scents communicate what a dog likes to eat, serve to identify the gender and mood of the other dog. They can obtain general information from the other, but to obtain more detailed information, they must approach in a more personal way, for this reason the dogs smell the anal region, since in it there are perianal glands loaded with pheromones with a unique and characteristic odor of each animal.

Physiology and behavior of canine smell

The dog's nose occupies a prominent space on their head, and has several main functions: breathing, detecting specific odors, capturing small particles that can be dangerous to their health, heating and humidifying the air breathed, etc. Uniquely designed, dogs' noses allow them to inhale and exhale at the same time, and in fact they inhale constantly, specifically about 10 times per second, allowing them to have a constant flow of air.

They have front holes through which they inhale, while the lateral ones are for exhaling. The front holes are independent of each other, which allows the dog to determine the depth of the scent and interpret the distance at which the trail is located. Something like having a 3D sense of smell.

Dogs have moist noses, for them this humidity is very important since in this way they can better capture the aromatic particles. Bearing in mind that smell is their main sense, we must make sure that our dog is sufficiently hydrated to guarantee the humidity of their nose.

A singular organ: the vomeronasal or Jacobssen organ

Among the many differences that we find between the sense of smell of dogs and ours, is the Jacobssen or vomeronasal organ. This organ, responsible for detecting pheromones is located at the tip of the palate.

Sometimes you might have noticed that your dog stops to lick urine and immediately begins to move their jaw as if trembling. What’s happening is that with their tongue, they’re displacing the liquid towards the opening of this organ, located just behind the upper central incisors. Through this organ our dog can acquire more information at the hormonal level of the other animal.

This organ serves as a secondary olfactory system designed specifically for chemical communication. The nerves of the Jacobssen's organ lead directly to the brain and are different from the other nerves of the nose in that they don’t respond to ordinary odors. In fact, they respond to scents that don't have much of an odor, so in other words, this organ is capable of detecting "undetectable" odors. This is especially useful for reproductive functions and with other animals of the opposite gender.

Do all dogs have the same capacity?

In addition to a genetic predisposition, there are breeds with more capacity than others when it comes to interpreting and recognizing smells. There are also dogs with behavioral attributes that make them more likely to have a better sense of smell, such as motivation, a desire to learn, their ability to learn or the ability to work with people.

Age also plays an important role, since over the years a dog can lose their ability to smell. However, compared to younger dogs, older dogs have much more long-term memory for odors, which allows them to manage more complex olfactory information.

As for sex, it has been found that the olfactory cells of females are more active than those of males.

What capacities does their smell bring to them?

Thanks to the development and characteristics of their sense of smell, dogs can capture not only present information, but also past information about the environment, such as, for example, who has passed by that place, and how long ago.

This complex network of odor mixtures creates a three-dimensional image of the world around the dog over time, playing a fundamental role in maintaining basic activities such as finding food, recognizing threats, or finding a reproductive partner.

When a dog is new to a territory, they can sniff a tree and determine that other dogs live in the neighborhood. They can sniff a guest's pants and get a good impression of where this person lives, and if they have any other pets at home.
Your dog doesn’t need to see you to be able to identify you. Humans have a unique innate essence that differentiates us from other human beings, so when you are close to home, your dog will surely know it before anyone else.

However, they are also capable of detecting fear or anxiety through smell. When we are stressed or scared, we secrete specific hormones such as adrenaline, which can be detected by dogs, although we can’t smell it. Also, when we have anxiety, our heart rate and blood pressure increase, which brings chemicals to the surface of the skin where dogs can smell them more easily, so if you are feeling low, even if nobody seems to notice it, surely your best friend will do.

A potential to take advantage of

Humans have taken advantage of the capabilities of our best friends in detecting drugs, explosives, and even different diseases such as cancer, diabetes, or infectious diseases. However, humans do not yet know the potential of canine smell until we have a full understanding of it, which allows us to adjust human-dog cooperation techniques to obtain the best results. Therefore, the use of dogs' olfactory abilities is still in human perception and learning, rather than the dog's olfactory system.

We are going to review the applications of smell in dogs in human activities:

Illegal and dangerous substance detection

The main function of working tracking dogs is related to the detection of illegal and dangerous substances. Dogs trained for this matter can find everything from explosives to illegal drugs such as cocaine, heroin, methamphetamine, and marijuana.

Training dogs are considered to be a very reliable, versatile and economical method as they are more effective than specialized instruments, being able to discriminate and locate target essences while ignoring all other interfering essences.

Detection of biological essences

Dogs are also able to detect the biological essences of people, or what is the same, they can identify a specific person among other people, even when the scent is mixed with more powerful scents.

As an example, a dog can identify the passage of a human scent through the center of a very busy city after 48 hours from its passage, with an accuracy of 77.5%.

Detection of other living beings

Just as they can detect people, they also can detect other living beings, which can be of great help when it comes to identifying invasive fauna, or for monitoring endangered species.

Within the field of agriculture, dogs are capable of identifying toxic particles in crops in very early stages of development, which can be of great help in avoiding losses later on.

Recognition of the physiological state by smell

Detection of the phase of the reproductive cycle

Dogs can identify better than a laboratory test in which exact phase the female is in her reproductive cycle thanks to the scent of the pheromones released.

Recognition of the emotional state

They are also capable of interpreting chemical signals given off by other animals, including humans, and identifying emotions through smell. This is because, according to our emotions, we release a series of chemical compositions that can be perceived by the dog.

Detection of diseases in humans and animals

It has also been proven that trained dogs can detect variations in urine caused by diseases and certain pathogens. From forecasting hypoglycemic episodes in diabetics, to identifying people infected with malaria through skin odor, as well as detecting cancer through exhaled air, urine, feces, and tissue samples.


In general, dogs' innate olfactory abilities make them more sensitive detectors than the best human-made analytical instruments. However, there are several aspects that undermine the credibility of canine olfactory abilities, and put them in constant doubt, and therefore their use is not as common as we might expect.

The main problem with an objective evaluation in canine detectors is that they are living beings and are constantly changing, depending on both internal and external factors. Thus, they are animals with incredible potential that can help us significantly but depending on what tasks it is, it’s always better to compare them with other tests to be more certain.

Considering the sensory difference that we have with our dogs, understanding that they have a totally different perception than ours can be of great help when communicating with them and trying to understand them. We must be aware that there are many things that they are not able to see with their eyes, although they can detect through smell.

We still have a long way to go to get close to understanding what their sense of smell is, but with information and learning, we can get a little closer to the idea.