How Dogs and Cats Use Scent to Communicate: The Science of Smell

You see a tree your dog has already sniffed three times this week.

Your dog may smell an entirely different version of it every time.

Another animal may have passed by. A urine mark may be newer or weaker. Rain, heat, wind, and time may have changed which odor molecules remain available.

Meanwhile, your cat rubs a cheek along the same corner of the sofa again.

To us, both behaviors can look repetitive.

To dogs and cats, scent is part of the information landscape.

Quick Answer: Dogs and cats use ordinary smell, chemical signals, scent-associated behavior, and a specialized vomeronasal system to gather information about their surroundings and other animals. Dogs rely heavily on sniffing and odor investigation, while cats commonly interact with scent through facial rubbing, urine marking, scratching, and investigation of familiar environments. Science supports important social roles for odor, but it cannot translate every sniff or scent mark into an exact human-language message.

Why Smell Matters So Much to Dogs and Cats

Humans tend to organize the world visually.

We notice the color of the house, the person crossing the street, or the car parked beside us.

Dogs and cats use vision too, but chemical information contributes heavily to how they investigate food, places, animals, people, territory, and familiar environments.

For dogs in particular, olfaction is supported by specialized nasal anatomy, airflow, neural processing, and an extraordinary ability to learn and discriminate odors.

That does not mean every dog has exactly the same nose.

Breed anatomy, skull shape, genetics, health, age, experience, motivation, environment, and training can all influence olfactory performance.

Be careful with famous nose statistics. Figures such as “300 million smell receptors” are commonly quoted for dogs and may be reasonable estimates for some highly scent-oriented breeds, but they should not be treated as an exact receptor count for every dog—or converted into simplistic claims such as dogs having “40 times more smell brain power.”

How a Dog's Nose Samples Odor

Inside a dog's nasal cavity are complex bony structures called turbinates.

They greatly increase the surface area available to nasal tissues, including the olfactory epithelium containing odor-sensitive receptor neurons.

During active sniffing, airflow is not simply drawn straight toward the lungs.

Research on canine nasal airflow shows that a portion of incoming air is directed toward the olfactory region, where odor molecules can interact with sensory tissue while the remainder follows the respiratory pathway.

Repeated sniffing therefore does more than make a dog look intensely interested. It is part of how the animal actively samples chemical information.

Signals from the nose then travel through olfactory neural pathways to brain regions involved in odor discrimination, learning, memory, and behavior.

That helps explain why smell can become deeply connected to places, routines, individuals, and learned expectations.

Cats Depend on Smell More Than Many People Realize

Dogs dominate popular conversations about smell, but cats also rely heavily on olfactory information.

A cat uses odor when investigating:

• Food
• Other cats
• People
• New objects
• Resting areas
• Doors and travel routes
• Changes in territory
• Objects returning from unfamiliar places

This is one reason something that looks unchanged to you can suddenly become suspicious to a cat after cleaning, travel, veterinary care, or contact with another animal.

A 2025 study also found that domestic cats behaved differently when investigating familiar versus unfamiliar human odor samples.

That supports the importance of human scent to cats, although the researchers cautioned that more work is needed before claiming cats can identify a specific person from odor alone.

What Is the Vomeronasal Organ?

Dogs and cats possess another chemical-sensing structure in addition to the main olfactory system.

The vomeronasal organ (VNO), sometimes called Jacobson's organ, is especially associated with detection of certain chemical signals involved in social and reproductive communication.

It works alongside ordinary olfaction rather than replacing it.

Why Does a Cat Make an Open-Mouth “Grimace” After Sniffing?

You may see a cat investigate an odor, raise the head slightly, part the mouth, and retract the upper lip.

This is the flehmen response.

Merck Veterinary Manual describes the behavior as helping expose chemical cues to the vomeronasal system.

Dogs possess a vomeronasal system as well and also use chemical signals as part of social communication.

How Dogs Communicate Through Scent

For dogs, sniffing is not just food detection.

Scent marking and scent investigation are important components of canine social communication.

Dogs commonly investigate:

• Urine marks
• Other dogs' bodies
• Feces and elimination sites
• Ground-scratching locations
• Objects carrying other animals' odors

These odor sources can contain biologically relevant information about the individual that produced them.

Research and veterinary behavior literature support roles for chemical signals in individual recognition, reproductive communication, social investigation, and marking behavior.

What science cannot currently do is translate every natural scent mark into a complete message containing another dog's exact age, health status, social “rank,” mood, diet, and personal history.

The dog is gathering information. We should be careful about pretending we know the entire content of that information.

Why Do Dogs Sniff Each Other's Rear Ends?

The anogenital region contains strong individual odors, including secretions from tissues and glands in the area.

Investigating that region therefore provides chemical information during canine social encounters.

Calling it a canine “handshake” can be a useful shorthand.

Calling it a complete medical and psychological scan is not.

Can Dogs Smell Human Stress?

There is good experimental evidence that dogs can detect odor changes associated with acute human stress.

In a controlled study, trained dogs distinguished combined breath-and-sweat samples collected from people before and after a psychological stress task.

The evidence supports changes in the overall pattern of volatile compounds associated with the human physiological stress response.

It does not show that dogs simply detect one molecule labeled “cortisol” and instantly understand the person's emotional story.

For the full evidence—including how facial expression, voice, movement, and scent can work together—see How Dogs Read Human Emotions: What Science Really Shows.

How Cats Use Scent Around the Home

Current feline behavior guidance describes scent as an important part of both social communication and environmental familiarity.

Facial Rubbing and Bunting

Cats have sebaceous glands concentrated in several areas of the body, including parts of the face.

When a cat rubs the cheek or side of the face against furniture, doorways, another cat, or a person, chemical material can be deposited on the contacted surface.

Facial rubbing often occurs in familiar social and environmental contexts.

It is therefore reasonable to view it as part of feline scent communication and maintenance of a familiar odor environment.

But “my cat is rubbing on me because I am now their property” is a human interpretation, not a literal translation demonstrated by science.

Scratching Leaves More Than One Kind of Mark

Scratching has several functions, including claw maintenance and stretching.

It also leaves an obvious visual mark, and chemical material from the paws may contribute additional information.

Veterinary behavior references commonly include scratching among feline visual and olfactory marking behaviors.

However, newer research has questioned how strongly we can conclude that scent marking is the primary motivation for unwanted household scratching.

The more accurate practical conclusion is:

Scratching can leave visual and chemical cues, but not every scratched sofa should be interpreted as a deliberate territorial scent message.

Placement still matters because cats often scratch in socially and physically useful locations rather than in the hidden corner where humans wish the scratching post would stay.

If furniture scratching is becoming a problem, our guide to cat scratching posts and placement covers the practical side separately.

Urine Marking Is Not the Same as Ordinary House-Soiling

Urine spraying can function as feline chemical communication.

Typical urine marking often involves a standing posture, raised or quivering tail, and a relatively small amount of urine directed toward a vertical surface.

But not every urine deposit outside the litter box is a scent mark.

House-soiling may also occur with:

• Lower urinary tract disease
• Pain
• Litter-box aversion
• Intercat conflict
• Environmental stress
• Mobility problems
• Other medical conditions

A sudden elimination change deserves investigation. Do not label new inappropriate urination as “territorial scent marking” before medical and litter-box causes have been considered.

Familiar Scent Can Be Part of a Cat's Sense of Home

A cat's normal environment contains overlapping odors from the cat, people, other animals, fabrics, furniture, food areas, beds, and frequently used pathways.

When that odor landscape changes abruptly, some cats may react.

A classic example occurs when one cat returns from the veterinary clinic smelling unfamiliar to another cat in the household.

Likewise, aggressively cleaning every rubbed, slept-on, or frequently used surface at once can alter more of the sensory environment than an owner realizes.

That does not mean a cat-friendly home should be dirty.

It means familiarity has a scent component.

This becomes especially useful when introducing cats. Our room-by-room guide to introducing a new cat explains why gradual exposure—including controlled scent familiarity—can be more effective than simply placing unfamiliar cats together.

Should You Let Your Dog Sniff on Walks?

Yes, when the environment is safe.

Sniffing is normal, species-typical exploratory behavior, and giving a dog opportunities to investigate odors is a reasonable form of enrichment.

But the internet has turned that sensible idea into some very specific claims that science does not support.

There is no established universal formula such as:

“20 minutes of sniffing equals 45 minutes—or an hour—of exercise.”

A Walk Has Two Maps

Your map may be mostly about distance.

How many blocks did we walk?

How fast?

How far?

Your dog's experience can include another map built partly from odor.

Who passed here?

What changed?

Where does this trail continue?

Your map is on the sidewalk. Your dog's is partly in the air and on the ground.

That does not mean every walk must stop at every blade of grass.

It does mean that repeatedly preventing every safe sniffing opportunity removes an important part of canine exploration.

What Does Research Say About Scent Work?

Recreational scent work and sniff-oriented walks have become popular companion-dog activities.

A scoping review of the research identified studies involving working, shelter, and companion dogs but also highlighted a major evidence gap: there is still limited direct research showing how participation in scent-based activities affects long-term welfare in ordinary pet dogs.

Studies published in 2026 add useful information without producing a simple “scent work is uniquely calming” conclusion.

Research comparing scent-work and traditional training classes found behavioral changes and benefits across training conditions, while another study measuring dogs during and after scent work found behavioral differences but minimal differences in several heart-rate-variability measures compared with control conditions.

Let dogs sniff because sniffing is normal and meaningful—not because someone promised a mathematical conversion between nose time and exercise time.

How to Add More Sniffing Without Overcomplicating It

You do not need a formal scent-work class to let a dog use their nose.

Depending on the dog, simple options can include:

• Allowing designated sniffing portions of walks
• Using a comfortably loose leash where safe
• Scatter feeding in an appropriate secure area
• Hiding food around a safe room
• Using a snuffle mat
• Playing simple food-search games
• Trying beginner scent-work exercises

Sniffing should complement—not replace—physical activity, training, social needs, sleep, and veterinary care appropriate for the individual dog.

Avoid allowing investigation of garbage, feces, toxic materials, sharp objects, or areas that may have been treated with unknown chemicals.

More Odor Is Not Automatically Better Enrichment

It is easy to take the idea of scent enrichment too literally.

Adding concentrated perfume, fragrance oils, or essential oils to a room is not equivalent to allowing a dog or cat to investigate normal environmental odors.

Avoid DIY concentrated-fragrance experiments. Strongly scented products can irritate animals, and some substances—including some essential oils—can create toxicity risks depending on the chemical, species, concentration, and route of exposure.

Good scent enrichment provides an opportunity to investigate and move away. It should not trap an animal beside an intense odor.

What About Synthetic Pheromone Products?

Synthetic pheromone products are available for both dogs and cats, but the evidence varies by product and situation.

In cats, pheromone products are sometimes used as an adjunct to environmental and behavioral management for problems such as urine marking, scratching, introductions, and stress-related situations.

Recent feline clinical guidance continues to treat them as a possible adjunct, not a stand-alone answer to medical or behavioral disease.

If a cat suddenly begins spraying, scratching excessively, hiding, fighting, or eliminating outside the litter box, adding a diffuser should not replace investigation of the underlying cause.

Scent Is Only One Part of Communication

Dogs and cats rarely communicate through only one sensory channel.

They combine chemical information with:

• Body posture
• Facial expression
• Ear and tail position
• Movement
• Vocalization
• Touch
• Context
• Previous experience

Our dog and cat body-language guide explains how to read the visible side of that communication without relying on one isolated signal.

When a Change in Smell-Related Behavior May Be Medical

A sudden change in sniffing, food interest, facial rubbing, marking, or response to familiar odors can sometimes reflect illness rather than social communication.

Contact your veterinarian when a meaningful new behavior occurs with signs such as:

• Nasal discharge
• Repeated sneezing
• Difficulty breathing through the nose
• Reduced appetite
• Facial pain or swelling
• Neurological changes
• Sudden urine marking or house-soiling
• Major behavior change

Reduced olfactory ability can occur with nasal or neurological disease, although true smell loss can be difficult for an owner to recognize directly.

A Better Way to Read the Scent World

• Let safe sniffing happen. It is normal exploratory behavior for dogs.
• Respect familiar scent. Odor is part of how cats experience territory and social environments.
• Don't overtranslate. A scent mark carries information, but we cannot decode every detail.
• Don't assume every cat rub or scratch means ownership or territory.
• Distinguish urine marking from medical or litter-box problems.
• Treat scent enrichment as enrichment—not a replacement for exercise or behavioral treatment.
• Give animals choice. They should be able to investigate an odor or move away from it.

Sources & Editorial Standards

• Merck Veterinary Manual — Social Behavior and Communication of Dogs
• Merck Veterinary Manual — Social Behavior and Communication of Cats
• The Role of Olfaction in Dogs: Evolution, Biology, and Human-Oriented Work (2026)
• Olfaction in Canine Cognitive and Emotional Processes — Review
• Dogs Can Discriminate Human Baseline and Psychological Stress Odours
• Behavioral Responses of Domestic Cats to Human Odor (2025)
• The Value of Sniffing: A Scoping Review of Scent Activities for Canines
• Heart Rate Variability and Behaviour in Dogs During and After Scent Work (2026)

Editorial note: Chemical communication is difficult for humans to interpret because we cannot directly perceive most of the olfactory information available to dogs and cats. This guide therefore distinguishes established anatomy and observable scent-related behavior from speculative claims assigning precise human-language meanings to individual odors, scent marks, or sniffing patterns.

The Bottom Line

The next time your dog stops at a tree you have passed a hundred times, remember that the chemical information may have changed since yesterday.

And when your cat rubs the same corner of the sofa again, the behavior may be contributing to a familiar sensory environment rather than making a literal declaration that the furniture now belongs to them.

Dogs and cats live in a chemical world we can only partly perceive.

Give dogs safe opportunities to investigate it.

Respect the role familiar scent plays for cats.

And resist translating every smell into an elaborate sentence science cannot actually read.

Scent is a major part of your pet's world. Our job is not to pretend we can smell the whole message—it's to give them enough space to use the sense they already have.