Couples can now take a DNA test to try and find out whether they are soulmates or a bad genetic match. Long-term partners can compare their genetic profiles in a bid to find out whether they are compatible.

The tests are based on the idea that men and women are most attracted to people whose HLA (human leukocyte antigen) molecules are completely different to their own.

Research which was carried out in Switzerland by the University of Bern asked women to smell T-shirts which had been worn by men for three days. They were then asked to rank them for attractiveness and it was found they favoured the T-shirts belonging to men with the HLA molecules which varied the most from their own.

HLA genes play an important part in the body’s immune system. It is believed that people are attracted to people with different HLA genes because this means their children are likely to be immune to more diseases making them stronger and healthier.

Daniel Davis, Director of Research at the University of Manchester’s Collaborative Centre for Inflammation Research, wrote a book in 2013 called The Compatibility Gene.

He said: “My book is about the few genes – our compatibility genes – that vary the most between each of us. First and foremost these are immune system genes; they control how we combat disease.

“But recent research shows that they may be even more important than we once thought – there is evidence that they can influence how our brains are wired, how attractive we are, even how likely we are to reproduce.’’

Tests claim to predict whether people are a suitable match

Prof Davis and his wife sent samples of their saliva off to the British charity the Anthony Nolan Trust, which helps match people who need transplants with suitable donors. The charity found that he had an unusual set of compatibility genes while those belonging to his wife, Katie, were more common.

He said: “It’s not that any of my individual genes are unusual, but the combination of them is rare because they are usually found in different parts of the world. After being pleased that my genes were quite rare – which according to those smelly T-shirt experiments would mean lots of women would like my scent – I then realised this might not be so useful if I ever needed a transplant.

“In fact the advice they gave me was: Just don’t get ill!”

Of course, most people will choose to follow their instincts when it comes to choosing a partner, rather than looking at the results of a DNA test. And it is not known how accurately the so-called matchmaking kits can predict the success of a relationship as there are no many other factors involved in whether couples will stay together or break up.

However, there are occasions when the results of DNA tests can be crucial to the future of a relationship. Doubts over the paternity of a child can cause enormous stress and worry, which can lead to separation and divorce.

Taking a paternity test will put an end to the uncertainty and allow both parties to move forward knowing the truth. Tests can be discreetly ordered online and the results will remain strictly confidential.