Finally, the Human Sense of Smell May Not Be as Weak as We Think

When we hear that ants can detect cancer and dogs can sense our stress through smell, our humble nose—which stops working entirely at the slightest cold—might seem rather unimpressive. Even in scientific circles, it is accepted that the human sense of smell is “slower” than sight or hearing. However, although our sense of smell is far from rivaling that of many animals, it is not as bad as most people believe. According to a new study, humans can detect subtle odor changes in just a few milliseconds, as quickly as they notice a change in color.

An Experiment to Test Our Sense of Smell

Researchers from the University of the Chinese Academy of Sciences and Ohio State University developed an inhalation-triggered device equipped with one-way valves to ensure odors travel in a single direction. The setup also includes Teflon tubes that deliver scents to the human nose with a precision of 18 milliseconds.

In 649 sessions, the researchers asked 229 adults in China to wear this device and smell various combinations of scents—two odors presented in rapid succession during a single inhalation. These scents included apple, sweet floral fragrances, citrus aromas, and onion smells.

The goal of the experiment was to test whether participants could distinguish between two odors presented in one order and then in reverse, with varying intervals. While a single breath, which lasts only about three to five seconds on average, might seem to limit the speed at which we can detect smells, the scientists' findings told a very different story.

Extraordinary Results from Our Ordinary Nose

Published in Nature Human Behaviour, the study shows that our olfactory perception can capture subtle chemical changes within a single breath, challenging previous assumptions about the limits of our sense of smell. Earlier research suggested that it takes around 1,200 milliseconds to differentiate between two odor sequences.

However, “We were amazed to find that participants could distinguish two odors presented in one order and then reversed with latencies as short as 60 milliseconds,” said Dr. Wen Zhou, the study’s lead author and researcher at the Chinese Academy of Sciences in Beijing. “For comparison, the duration of a blink is about 180 milliseconds,” he added.

Testing with Meticulously Timed Odor Sequences

Over five experiments, the device enabled the presentation of two odors in rapid succession with exceptional precision. In one experiment, two odors—a fruity apple scent and a floral fragrance—were sequenced and delivered to participants' noses, with one odor arriving 120 to 180 milliseconds before the other. Participants correctly identified the order of the scents in 597 out of 952 trials, with an accuracy of 63%. Similar results were obtained with 70 additional participants exposed to lemon and onion scents.

What Are the Implications of This Research?

A Deeper Understanding of Human Smell

In the animal kingdom, the ability to distinguish odors during a single inhalation is critical for identifying what a scent is and where it might be located. “The demonstration that humans can distinguish odors as they change within a single breath shows that timing is crucial for the sense of smell across species. It also suggests that rhythm is a fundamental principle underlying olfactory function,” explained Dr. Sandeep Robert Datta, professor in the Department of Neurobiology at Harvard Medical School, who was not involved in the study.

“The study of human olfaction has historically lagged behind research on vision and hearing because we tend to think of ourselves as visual creatures that rely primarily on speech to communicate,” Datta added. He noted that these findings help “fill a critical gap in our understanding of how humans perceive odors.” The implications of this research go beyond the laboratory, offering fascinating insights into how smell shapes human behavior and interactions.

Health and Industry Applications

Recognizing the olfactory system's ability to quickly differentiate between subtle chemical differences could revolutionize industries that rely on scent, such as food and beverages, perfume manufacturing, and even healthcare. A more refined understanding of how we perceive odors over time could allow professionals to enhance flavor development, improve perfume design, and refine scent-based therapies.

“Our device could also have therapeutic applications, such as olfactory rehabilitation for patients suffering from loss of smell,” suggested Dr. Zhou. “More broadly, our findings could guide the design and development of electronic noses and olfactory virtual reality systems, which could have significant clinical benefits.”