It is the simplest of gestures to show a loved one how you feel this Valentine's Day. But it seems there's more to a kiss than you might think.
For the direction you turn reveals much about your relationship, scientists say.
Couples who are in love tend to lean to the right, while parents kissing their children favour the left, they found.
Previous research has shown that around 80 per cent of romantic couples turn to the right when kissing, regardless of whether they were right or left handed.
The scientists wanted to see if this also applied to parental kissing. They compared 161 images of romantic kisses, between mothers and fathers, and 529 images of parents kissing sons or daughters.
Their study confirmed the right-leaning bias for romantic couples - but found that parents kissing their children tended to turn the other way. The team, of the University of Saskatchewan in Canada, believe this is because the majority of parents cradle babies using their left arm and that, since they are most likely to kiss them while cradling them, they will tend to kiss to the left too.
This then becomes a habit.
Lead author Jennifer Sedgewick added: "A left-turn kissing bias could persist beyond the stage of cradling due to the repetitive movement in that direction since it may feel most natural." Miss Sedgewick said the left-turn bias for parental kissing was "a finding that is novel to kissing bias research".
The reason romantic couples kiss to the right is thought to be because they experience heightened activity on the left side of their brains when they enter a new relationship, which might guide them to turn right as they kiss. The researchers, whose findings were published in the journal Laterality, found there was no difference between the sexes in how they kissed.