The simple answer to the question of whether any relationship is "the one" seems to be that your ideal man or woman gets up your nose, scientists say.
In a new study, reported in the journal Biological Psychology, researchers looked for the first time at the effect of being born without a sense on smell on men and women's relationships, The Independent reported.
The research involved analysing data on men and women aged 18 to 46 with no sense of smell and comparing it with information from a healthy control group.
The results showed that men and women who were unable to smell had higher levels of social insecurity.
In men, but not in women, it led to fewer relationships. The men with a faulty sense of smell averaged two partners compared with 10 for healthy men.
One theory is that the lack of a sense of smell may make men less adventurous. They may have more problems assessing and communicating with other people.
The two groups of women had the same average number of sexual partners four. But the women who couldn't smell well lacked confidence in their partners: they were around 20 per cent less secure in their relationship.
Lacking a sense of smell had no impact on their relationships with close friends, suggesting that smell plays a role for women specifically when it comes to their partners.
Research is increasingly showing that olfaction, one of the oldest sensory systems but probably the least understood, has an important role in a large number of areas.
According to one study, women are more concerned about the smell than about the look of a potential mate, while men are the opposite.
Another study found that 13 per cent of men and 52 per cent of women have slept dressed in the clothing of another person, usually their partner, because of the smell.
"The sense of smell provides social information about others. Its absence is related with reduced social security in men and women, and affects partnership," said the researchers from the University of Dresden.
"Men exhibit much less explorative sexual behaviour and women are affected in a way that they feel less secure about their partner. Our results show the importance of the sense of smell for social behaviour," they said.
Phillip Hodson, a psychotherapist and author of How 'Perfect' Is Your Partner?, described the new study as "a very astute piece of work".
"Instead of testing pheromones which control moths but may not control humans they've studied the smell-disabled to see how they differ from the rest. And both sexes with faulty noses appear to be less than sexually confident," he said.
"We know the nose is a sexually interactive organ: it tends to run when we get aroused and often people sneeze when extremely excited," he said.