In Tokyo, thirty housecats were faced with a simple choice: three plastic tubes, three different smells. One held the scent of their beloved owner, another the odor of a total stranger, and the third was just clean and odorless. What the cats did next may subtly shift how we think about our feline companions.

According to the new study published in PLOS ONE, domestic cats can tell the difference between the scent of a familiar person and that of a stranger. They don’t just notice the difference; they show a clear preference for the unknown. The cats consistently spent more time sniffing the odors of strangers than the scent of their own owners or the blank control.

“This suggests cats use their olfaction for the recognition of humans,” wrote Yutaro Miyairi and his colleagues at the Tokyo University of Agriculture, who led the study.

A Nose for the Unknown

The experiment took place in each cat’s own home, a setting chosen to reduce stress and maximize cooperation, which is always tricky with cats. Each feline was introduced to three tubes: one swabbed with their owner’s scent, one with the scent of a stranger of the same sex as the owner, and one clean.

To collect the human scents, volunteers rubbed cotton swabs behind their ears, under their arms, and between their toes. The swabs were then placed into sterile tubes, minimizing contamination. To ensure nothing was skewed by colognes or recent food, the volunteers were asked to avoid strong-smelling products and spicy foods for 24 hours.

The cats sniffed these tubes while being filmed by a GoPro camera. When the researchers analyzed the videos frame by frame, a pattern emerged: the cats spent an average of 4.8 seconds sniffing the stranger’s odor—about twice as long as they spent on their owner’s scent (2.4 seconds) and even more compared to the blank swab (1.9 seconds).

“Sniffing an unknown stimulus for longer has been shown before in cats,” Hidehiko Uchiyama, the study’s senior author, told BBC. But the team stopped short of concluding that cats can identify specific people as their owner.

Left or Right Nostril?

To get more insights into what cats are doing, the researchers also recorded how the cats sniffed—specifically, which nostril they used.

When cats first encountered an unfamiliar odor, they preferred to lead with their right nostril. Over time, however, they began to shift to the left. This nostril-switching behavior mirrors patterns seen in other animals, including dogs and horses, and may reflect how the brain processes information.

“The left nostril is used for familiar odors, and the right nostril is used for new and alarming odors,” Uchiyama explained to The New York Times. “It is likely that the right brain is preferred for processing emotionally alarming odors.”

This type of behavior is known as “lateralization”—a bias in how one side of the brain or body handles certain tasks. In this case, the cats may be processing new human smells in their right hemisphere and switching to the left once the scent becomes familiar. However, it’s not entirely clear how to interpret these findings.

Dr. Carlo Siracusa, a veterinary behaviorist at the University of Pennsylvania, who was not involved in the study, urged caution. “The study did not prove that the right side of the brain is activated,” he noted. Brain scans, not behavior alone, would be needed to draw that conclusion. “Still,” he said, “this is a very important piece of information. This is how science works. You need to prove everything.”

Each Cat Has Its Own Personality

After their olfactory investigations, many of the cats rubbed their faces against the tubes—behavior that may seem like affection but serves a more utilitarian purpose in feline society: scent-marking.

Cats have glands on their cheeks that release pheromones when they rub objects. By doing so, they claim the object as part of their territory. In this study, cats were more likely to rub the side of their face that corresponded to the nostril they used for sniffing—another clue that sniffing may be the prelude to claiming.

Interestingly, cats that sniffed the stranger’s scent with one nostril often rubbed that same side of their face against the tube. And there was a pattern: rubbing behavior increased with higher scores in “impulsiveness” (toward blank tubes) and “closeness” with the owner (toward tubes containing the owner’s scent).

However, not all cats responded the same way. The researchers used a feline personality test—the so-called “Feline Five”—to analyze traits like neuroticism, agreeableness, and impulsiveness. They also used the CORS (Cat-Owner Relationship Scale) to measure emotional closeness.

Male cats with more neurotic personalities were more likely to sniff tubes repeatedly, suggesting anxiety or increased vigilance. Males scoring higher in agreeableness sniffed more calmly. Female cats, by contrast, showed no strong correlation between personality and behavior.

Moreover, the cats’ initial choice of which tube to sniff first seemed linked to personality. Cats that went for the blank tube first scored higher in neuroticism. Those that started with the known or unknown odors tended to be more agreeable and extraverted.

These subtle behavioral signatures hint at a deeper cognitive process. “The cat may have been able to perceive volatile odor molecules and discriminate between tubes containing human odor and blank tubes even before it put its nose close,” the authors suggested.

So, Do Cats Know Us by Smell?

That depends on what you mean by “know.” They recognize the scent, that’s for sure. But whether or not they pinpoint that scent to a particular individual is less clear.

“The odor stimuli used in this study were only those of known and unknown persons,” said Uchiyama. “Behavioral experiments in which cats are presented with multiple known-person odor stimuli would be needed.”

Serenella d’Ingeo, a researcher at the University of Bari who studies feline responses to human odor, agrees. “We don’t know how the animal felt during the sniffing,” she said. “We don’t know, for instance, whether the animal was relaxed or tense.”

She also noted that having the owners present during the trials might have influenced the cats’ behavior. “Owners present not only their visual presence but also their odor,” she said. “So of course if they present other odors that are different from their personal one, in a way they engage more the cat.”

The Bigger Picture

This study is part of a growing body of research suggesting that cats, despite their enigmatic ways, are deeply attuned to human cues. Previous work has shown that cats recognize their owner’s voice, follow human gaze, and adjust behavior in response to emotional odors.

Still, research on feline social cognition lags behind that of dogs. Cats often resist participation in behavioral experiments, a fact that makes this study—successfully engaging 30 cats in structured trials—all the more remarkable.

“I really commend this group of scientists for being successful in engaging 30 cats in doing this stuff,” said Dr. Siracusa. “Most cats want nothing to do with your research.”

So the next time your cat gives you a sniff, remember: they may be reading you—quite literally—like a book of smells.