What creates that initial spark between two people? Well, it's body odour, created by the genes involved in the immune system, and more specifically the DNA, say experts.

According to Tamara Brown, a Croatian geneticist based in Zurich, a section of the DNA called human leukocyte antigen plays a key role in searching for "true love" and the key lies in "secret signals" one picks up from another's body odour. "It's chemistry of attraction. Somebody might not be Brad Pitt-good-looking, but there's just something about them and you can't put your finger on it," Dr Brown was quoted by The Sunday Times as saying.

In fact, the catalyst for her study was the "T-shirt experiment", a Swiss study at the University of Bern carried out in the mid-1990s that screened the DNA of male and female volunteers, and then asked the women to smell T-shirts the men had worn for two nights and rate them for "attractiveness". The women, it turned out, preferred the smell of men with genes that were different from their own in this HLA section. All the women, except for those on the contraceptive pill, seem to affect their sense of smell.