By combining compounds in just the right mixture, researchers have worked out how to produce the olfactory equivalent of white noise

Wipe out that whiff (Image: Michael Blann/Getty)

HAS someone burned the toast and stunk out the kitchen again? Fire up the smell canceller and sniff freely. That’s the proposal from two researchers who are applying the principle behind noise cancelling headphones to noses.

Aural and visual signals are easy to manipulate because they are both based on waves, which can be described mathematically, leading to a huge variety of ways to manipulate a signal, like compression, filtering, and so on. It’s much harder to write down equations for the complex chemistry behind smells, which is why you can’t download the tempting waft of a bacon sandwich.

Now Kush Varshney of the IBM Thomas J. Watson Research Center in New York and his brother Lav Varshney of the University of Illinois at Urbana-Champaign say they have cracked it. The pair have created a mathematical model that predicts how humans perceive the smell of a particular substance based on its physical and chemical properties, by matching a database of compounds to another of perceived smells. One compound could smell 5.6 chalky, -3.2 celery and 0.8 cedar wood, for example, on a rating system from -5 to 10.


To cancel out a smell, they calculate which compounds provide the opposite ratings, giving a zero score across the board. Previous research has shown that an equal blend of around 30 compounds creates “white smell“, the neutral olfactory equivalent of white light or white noise. The Varshneys’ simulations show a blend of 38 compounds could almost completely cancel out the odours of onion, sauerkraut, Japanese fermented tuna and durian fruit, achieving white smell even in the presence of these notoriously pungent foods (arxiv.org/abs/1410.4865).

The pair haven’t built a smell cancelling device yet, but they are confident the maths will check out and it should be possible. They were inspired by IBM’s work with its advanced computer Watson, which is currently learning to cook by identifying the flavour compounds different ingredients have in common.

Previous attempts to digitise smells have led to the likes of the oPhone, a device that releases mixtures of compounds to recreate more than 300,000 smells, but these have never really taken off. That’s because smells linger, making it difficult to use such devices repeatedly. Cancellation might be able to fix this, as it is more sophisticated than simply masking an existing smell with a more powerful odour.

Noam Sobel of the Weizmann Institute of Science in Rehovot, Israel, invented the concept of white smell and is also working on a cancellation device, though without success so far. “I think the ideas are sound,” he says. But if white smell is the future, what does it actually smell of? “It’s not very pleasant, but it’s not foul. It’s not very edible smelling, but it doesn’t smell poisonous.”

This article appeared in print under the headline “Mix 38 scents to oust any smell”