It's sometimes hard to pinpoint exactly what it is that attracts us to someone. It might be their confidence, or their sense of humour, or you might just like the way they look.
A lot of research over the years has gone into trying to work out what it is that makes us fancy each other. Results have varied, showing women may like the smell of men who have a particular kind of diet, and men may find women in groups more attractive.
Some research has suggested we often go for people who share some of the same characteristics we do.
We've looked at a number of studies to try and get to the bottom of what makes us like the look of one person over another.
Here are 9 face traits that can make someone more attractive to us, according to science.
Studies such as this one published in the Journal of Comparative Psychology, and this one published in the Journal of Evolution & Human Behaviour, have shown that in experimental conditions, men and women both prefer faces that are more symmetrical.
A study on identical twins found that the twin with a more symmetrical face was considered more attractive. Even macaque monkeys have been observed gazing longer at symmetrical faces than asymmetrical ones.
One conclusion scientists have reached to explain this is that in evolutionary terms, we may consider a symmetrical face a result of good health. Having a face that developed in a symmetrical way could show you have "good genes," because you developed more successfully in the face of environmental pressures when you were in the womb.
However, in 2014, research from Brunel University in London compared facial symmetry of about 5,000 teenagers, and found there was no correlation between symmetry and overall health.
It's not an absolute rule, though. In fact, you can probably think of many celebrities you fancy who don't have symmetrical faces at all. Sometimes, like in the case of Milo Ventimiglia, a crooked smile is what adds to someone's charm.
In fact, absolute symmetry can make people look pretty weird. When attractive celebrities' faces are made to look symmetrical, they don't look quite right.
People tend to like faces that are distinctly average, or those that resemble others in the general population.
In 1878, a paper in Nature first noted that a bunch of faces blended together was considered more attractive than those on their own.
One study, published in the journal Human Nature, argued it could be because average faces represent a more diverse set of genes, which is often a genetic advantage in fighting off illnesses and parasites.