A single sniff is enough to detect slight odor changes

The sniffs we take to identify a smell last from one to three seconds. But is it possible for us to detect odor changes in an even shorter time? Yes, a new study finds — far more quickly.

A new device gives scientists precise control over odors. Using it, researchers showed that people can perceive odor changes in a fraction of a second. They reported their findings in the November 2024 Nature Human Behaviour.

“Intuitively, each sniff feels like taking a long-exposure shot of the chemical environment,” says Wen Zhou. She’s a psychology researcher at the Chinese Academy of Sciences in Beijing. When we detect a smell, that odor may seem complete and whole in that moment, she says. 

But new work by her team reveals a different story. They designed a device that picks up on a sniff as it starts, sensing pressure changes in the nose. That triggers the device to send out two odors — one close to the nose and the other a short distance away.

The team tested more than 200 people using the device. Each participant took a single sniff as the two chemical odors were released back-to-back. The device allowed the scientists to control the timing of the release with millisecond precision.

Some of the odors smelled like apples or flowers. Others smelled like onions or lemon. Participants reported which of the two odors they perceived, and in what order. 

Overall, those tested identified the sequence of the odors with better-than-chance accuracy. That was true even when the odors were delivered only 60 milliseconds apart.

These results suggest that the speed of our sense of smell is on par with that of our color perception.

Zhou next wants to find out what happens from sniff to sniff, since our noses can detect more than a trillion scents. “Sniffs are separated in time,” she says. How the brain processes the timing within and between sniffs is still an open question.

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