NOT many people can claim to have smelt the world’s worst odour, but Pamela Dalton ( pictured) also helped to invent it.

Six years ago, Dalton and her colleagues at the Monell Chemical Senses Centre in Philadelphia were asked by the US Department of Defense to study whether responses to malo-dours were universal. They may well be: during trials, the mixture they came up with, nicknamed stench soup, managed to disgust just about everybody.

The concoction is a combination of smells designed to repel and disgust. The formula has changed over the years, but it combines the odours of decomposition and vomit as well as a sweet, fruity smell.

Dalton, who has a PhD in experimental psychology, trained as a cognitive and sensory psychologist, studying how humans process information, especially sensory information. For the last 15 years she has investigated how people react to odours. Smells are the jokers of the sensory world, she says; they trick us.

“If I tell you to expect the smell of an apple and instead I give you peach, the first thing you’re going to try and do is to fit that smell into the apple category,”she says.

Dalton can think of plenty of applications for the stinky brew. “Odours are one of the quickest ways to get people to move away from something,” she says. “I’ve evacuated our building on several occasions because we’ve had an odour escape . . . Odours can keep people away more effectively than a sign saying ‘keep out’.”

When she was working on the formula for stench soup, Dalton got hundreds of e-mails from people with smelly suggestions. “[For example], five pounds of shrimp left in the refrigerator of a vacation home over winter,” she says. “Crazy stuff. But one of the things that helped me was appreciating just how important the sense of smell is to people’s lives. My boyfriend always tells me that no matter where I am, I should tell people I’m a librarian. If I say I do odour research, it’s thirty minutes later and I’m talking to some stranger at the airport.”

But Dalton loves her work. “To study human olfaction requires that you develop an interdisciplinary approach. You need to dabble in biology, chemistry, psychology and some physiology, but it’s very rewarding. Olfaction, taste and sensory irritation are some of the last sensory frontiers to yield their secrets. Being able to work in an area where major discoveries are being made regularly is very exciting.”

We may be familiar with Proust and his madeleines, but scientists still don’t know why smell is so strongly connected to memory. What scientists know most about is the periphery, the first few steps of how we perceive smells. What happens when the smell signal gets to the brain is unknown territory.

So we may not know why yet – but our sense of smell is clearly idiosyncratic. Dalton’s favourite smell is diesel exhaust. “I love living in cities,” she says. “There’s always a bus or truck going by.”

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