Doctor David Lewis is adamant: “Bad smells get up your nose – literally,” he says. “They have a negative effect on your brain. Pleasant smells have a positive effect and so it pays to have these in your house, especially if you are trying to sell it to a complete stranger.”

When thinking about moving to a new home, odour is not usually right up there with the main criteria of location, price and condition. But it is one of the three subsidiary Ss: sight (how it looks), sound (background noise) and smell (both pleasant and not so). And the homeowner often unwittingly contributes to the latter. “We all have a unique personal odour that is a product of what we eat and drink and our lifestyle,” explains Lewis. “Household pets are also a factor – both dogs and cats, although goldfish are quite neutral. All of these scents are transferred to your home so that every house has its own smell after a while,” says Lewis, a neuro­psychologist and director of research for Mind Lab, an independent consultancy that carries out scientific studies on the brain and its responses to various stimulants. He is particularly interested in BO – building odour.