Telling someone you fancy 'I really like you' could make him or her find you more attractive, research suggests.
Making eye contact and smiling have a similar effect, says Aberdeen University psychologist Dr Ben Jones.
His study, involving 230 men and women, found such social cues - which signal how much others fancy you - play a crucial role in attraction.
The work will appear in Psychological Science and will be presented at the BA Festival of Science in Liverpool.
Dr Jones said singletons could use his findings to help prevent wasting time chatting up people who were clearly not interested.
"Combining information about others' physical beauty with information about how attracted they appear to be to you allows you to allocate your social effort efficiently," he said.
In other words, avoid wasting time on attractive individuals who appear unlikely to reciprocate.
In the study, 230 men and women were asked to look at flash cards picturing a face with different expressions - making eye contact or not and smiling or not.
The volunteers were then asked to rate how attractive the faces were.
The preference for the attractive face was much stronger when people were judging those faces that were looking at them and smiling.
Dr Lynda Boothroyd, a psychologist at the University of Durham, said: "We like it when attractive people seem to be behaving positively towards us.
"And we seem to end up with people who are on our level in terms of attractiveness.
"Maybe one of the ways you learn your level of attractiveness is through how other people behave towards you."
I learned the most effective flirting technique as a teenager in an interview with Joan Collins. When you're talking with someone you fancy, privately imagine you're kissing him/her. Apparently this sends out the adequate body signals. It really, really works!
Cristina, Santiago, Chile
Is this really new? Thought everyone knows about this. I might also add that this finding applies only to one culture, certainly not universally. Smiling at perfect strangers is a striking habit in the US and Canada; in Germany or Britain, this could get you into trouble (although it is usually taken in the spirit offered). Just don't go trying this method in foreign countries, I would say.
D. Fear, Heidelberg, Germany
I saw this lovely face yesterday - when I smiled it smiled back and me, so I thought I had scored a hit. Then I realised I was looking in a mirror.
David Roberts, London
I've never bothered much with the stare and grin ritual, yet I've had no trouble finding partners. If you genuinely like somebody, it'll show, and they'll most likely take a shine to you. Just relax, be your genuine self, and all else will follow. Works for me every time.
Arthur Priest, Leicester England
Being a single male all my life, I find this little tidbit interesting. The eye contact, level of interest and attraction are all factors, but so is the 'instinctual feeling' we all get in regards to someone being interested. Personally, I've behaved in the same manner as listed above, but have never felt that interest or attraction returned.
Jason Smeraka, Victoria, BC, Canada
Yes indeed I do feel more positive and less anxious about approaching someone who I find attractive when they show positive facial and body gestures, things such as smiling and simply looking into your eyes goes a long way! That simply cannot be disputed in my mind.
Thabang Mafela, Tshwane, South Africa
There has been a billion of these studies, and all of them say the same thing, which is if you show affection, it is more likely that it would be reciprocated. Which is a quite obvious result. But then they have a bunch of speculations at the end that never get tested. And on top of that, they give some suggestions for those who want affection reciprocated and say show some affection, obvious again! A more interesting study would be on the dynamics on how affection effects social standing (i.e. those who are afraid to take friendships to another level because they are afraid of social consequences).
Jacob Kinnun, Tucson, AZ, US