Receiving a smile from a friend or relative generates much higher levels of stimulation to the brain and the heart than being given money or having a cigarette, according to clinical tests.
But the amount of pleasure depends on who is smiling: a child’s face or that of a celebrity has a much better effect than a politician or a member of the Royal family. The study found that smiles from Geri Halliwell and Robbie Williams created much greater stimulation and pleasure than those by Tony Blair or Prince William.
The research, carried out by the computer giant Hewlett Packard, suggests simple human interaction is still worth far more than material pleasure. The research found that Scots were among the most likely in Britain to return a smile from a stranger.
Tests were carried out on adult volunteers to determine the effects of various factors in creating a short-term high. An electromagnetic brain scan machine and heart-rate monitor measured brain and heart activity to create a "mood-boosting value" for various stimuli. The tests were carried out on 109 volunteers and followed up by a poll of 1,000 adults.
In the clinical tests, the subjects were shown photos of friends, family and loved ones smiling, given money and chocolate.
Participants who were shown a child’s smile experienced the same level of stimulation as they would have had from eating 2,000 chocolate bars or receiving 16,000 in cash.
The subsequent survey found that seeing a smile was more likely to create a short-term high than sex, chocolate and shopping, ranked in that order behind smiling.
Behind these came receiving money - even just 10 - having a cigarette, coffee or taking drugs, in the list of what provides Britons with a short-term high.
While the smile of a child equated to 2,000 bars of chocolate or 16,000, that of a loved one was worth about 600 chocolate treats or 8,500. The smile of a friend was worth 145 of feelgood, or about 200 bars of chocolate.
The clinical tests were analysed by the psychologist Dr David Lewis, the author of The Secret Language of Success.
He said: "The powerful emotions triggered when someone important in our lives smiles at us and we smile back changes our brain chemistry.
"It creates what is termed a ‘halo’ effect that helps us remember other happy events more vividly, feel more optimistic, more positive and more motivated."
In a test, members of the public were shown smiles without being told who they belonged to and points were awarded for trustworthiness, warmth, sincerity, honesty and other categories. They were shown celebrities, politicians and Royals, and each ended up with a total score out of 100.
Political smiles were voted the worst, particularly for trust, followed by royalty. The best celebrity smiles belonged to Robbie Williams and Geri Halliwell.
Williams scored 90, Halliwell got 79, while Victoria Beckham received just 69, but this was more than the highest Royal, Prince Harry with 64, followed by the Queen, who got 60.
Prince William scored 55, the same as the Prime Minister, Tony Blair, but both were lower than Charles Kennedy, the Liberal Democrat leader, who scored 60. Camilla Parker Bowles could only manage 46 out of 100 but this was still better than Michael Howard’s 40 score - the lowest of all.
Vic Foti, of Hewlett Packard, added: "Feeling like a million dollars is a common saying, but this research shows that if you receive enough smiles, you actually can."
Dr Lewis added: "In contrast [to loved ones] the fake smiles of royalty and politicians are detected and have the opposite effect, giving the person an untrustworthy and hypocritical image.
"The importance of a smile and of face-to-face contact cannot be underestimated. Smiles are incredibly contagious - like yawns, if you smile, the other person usually smiles back. Sometimes we’re a bit inhibited in the UK and think that if we smile it might be misinterpreted."
Dr Lewis explained that slight differences in the shape of the face could give away an insincere smile.
He said: "If people are laughing a genuine laugh they get two little pouches underneath their eyes. Without that, it is definitely a forced smile.
"Any tension around the mouth is usually a dead giveaway, too."
Mr Foti, whose company also makes digital cameras, added: "It’s ironic that with the amount of photo opportunities politicians and royalty create to improve their image, they are actually harming it by faking their smiles in pictures."
The research found that Scots were among the most likely in Britain to return a smile. Four in five of those smiled at by researchers in Edinburgh returned the smile (79 per cent) - behind Manchester (84 per cent) but ahead of all other major cities. The worst was London, on 47 per cent.
When asked: "What gives you the best short-term high?", the responses from people in Scotland were as follows: smiling (36 per cent - the second highest figure across the UK) making love (20 per cent - higher than the national average), listening to your favourite song (13 per cent), shopping (7 per cent), eating a bar of chocolate (4 per cent).
Jeffrey Bray, a lecturer in retail psychology at Bournemouth University, said the impact of smiles was an important lesson for companies amid the current trend towards call centres and internet shopping.
He said: "The high street still has the pleasure part of the shopping experience and smiling from shop assistants is a big part of that.
"Consumers are also smart at spotting insincerity in smiles. We’ve all heard phrases like ‘Did you find what you were wanting today?’ and ‘Have a nice day’ and they come across as robotic.
"Shop staff who are happy and genuinely engaged by their work will convey that sense of pleasure to shoppers."
He added: "Despite the importance of a smile, it is interesting to note that relatively few types of packaging use human faces or smiles to attract attention - it tends to be eye-catching designs that first work on the shelves."