This week: What does our odour really mean?

A new study suggests that every person has their own unique smell or "odourprint" that could in future be used to identify individuals in the same way as a fingerprint or DNA test. But human scent is more than a marker - it has many powerful effects, even if we are not always aware of them.

How can you identify someone from their smell when your odour is affected by what you eat?

The research suggests that even if you go overboard with garlic and chilli, your underlying signature odour remains unchanged. Experiments with mice found that those who were given strong-smelling foods were still recognised by their peers.

That's mice. Surely the human nose isn't sensitive enough to detect someone's particular odour?

You'd be surprised. We might not be conscious of it, but other people's signature odour to some extent governs how we feel about them. Take the T-shirt test. This is a laboratory experiment developed by evolutionary biologists in which women are presented with a series of identical T-shirts that have been worn by different men. They are invited to sniff the T-shirts and say which they prefer. Experiments show that women generally prefer the scent of men who have very different immune-system gene variants from themselves. The evolutionary benefit is clear: any offspring should inherit an immune system giving them protection from a wide range of different pathogens.

Is this anything to do with pheromones? They're important in sexual attraction, aren't they?

Pheromones are odourless chemical secretions that are important in the animal kingdom, but there is more limited evidence of their potency in humans. That said, one fascinating study by a team from the University of Chicago found that women's libido increased by up to 50% when they were exposed to the pheromones of other women who were breastfeeding, apparently because it signalled to them on an unconscious level that the time was right to try for a baby. In an evolutionary context, the presence of other nursing mothers would suggest the environment was safe for child-rearing and food was plentiful.

Some other tests provide evidence that men regard women as more attractive when unwittingly exposed to female pheromones. But what really appears to make a difference is perfume. An intoxicating, sexy scent can be very stimulating to a man. A study published in the Journal of Sexual Medicine earlier this year found that perfume activated the same regions of the brain as visual stimulation, a very important part of male sexual attraction.

What is the benefit of analysing smells, apart from developing yet more surveillance technologies?

The scientists at the Monell Chemical Senses Centre in Philadelphia who have been researching human odourprints believe a smell test could be beneficial in making early diagnoses of certain diseases, including cancer. They tested the air above certain skin-cancer tumours and found it had a profile of chemical compounds that was distinct from the air located above healthy skin. The team have also shown that the odour profiles of skin from different parts of the body, such as the forearm and the upper back, differ. A study published in the British Journal of Dermatology detailed almost 100 different chemical compounds coming from skin.

All this means that, in future, odour profiling could give doctors a good idea of whether a lesion is diseased or not.