Stubble is the way to win a woman’s heart, a study has shown. Researchers found that women are more attracted to men with stubbly chins than those with clean-shaven faces or full beards.

Women participating in the research rated men with stubble as tough, mature, aggressive, dominant and masculine - and as the best romantic partners, either for a fling or a long-term relationships.

Hair apparent: George Clooney, Colin Farrell, David Beckham and Will Smith

The findings of the experiment, carried out on British women aged 18 to 44, could explain the appeal of actors such as George Clooney and Brad Pitt who cultivate their unshaven look.

The explanation for the preference is not clear, but experts in human evolution say that that facial hair may be a signal of aggression because it boosts the apparent size of the lower jaw, emphasising the teeth as weapons.

Psychologists at Northumbria University who carried out the new study believe that stubbly men may offer women the best worlds - not too strongly masculine, but mature and with the potential to grow a full beard.

The researchers carried out the study using computer technology to alter pictures of 15 men’s faces so that they displayed different degrees of hairiness. Five levels of facial hair were used - clean-shaven, light stubble, heavy stubble, light beard and full beard.

The pictures were shown to 76 women who were asked to rate them for masculinity, aggression, dominance, attractiveness, age, and social maturity. They were also asked how desirable each man would be as a short-term or long-term partner. Faces with full beards were judged to be the most masculine, aggressive and socially mature. They were also thought to look five years older.

They were rated the least attractive and the worst choice for a short-term relationship. Men with light beards were considered the most dominant. Those with light stubble were rated the most attractive and as the ideal romantic partner for the short or long term. Clean-shaven men finished bottom for masculinity, dominance, aggression, and social maturity, and they were the least favoured choice as a long-term partner. They came second-to-last for attractiveness.

Writing in the journal Personality and Individual Differences, the researchers conclude: “Facial hair, or beardedness, is a powerful sociosexual signal, and an obvious biological marker of sexual maturity.

"Facial hair may have been sexually selected by females on the basis of associated male success, despite its threatening appearance. Clean-shaven faces therefore may suggest appeasement, as well as being an obvious sign of sexual immaturity.

"Increasing levels of facial hair were associated with increased perceptions of aggression, in that bearded faces were perceived as being the most aggressive, whilst clean-shaven faces were rated as being the least aggressive. And as facial hair increased in a linear fashion, so did female ratings of masculinity and dominance.

"In desirability for a short-term relationship, a female preference for male faces with stubble or light beard was found, with clean-shaven and fully bearded faces being the least preferred. This indicates that females are not selecting faces displaying relatively high or low masculinity, but are rather preferring males who are clearly mature - post-pubertal - but not too masculinised. The same pattern was found for preferences for a long-term relationship."

The researchers now want to extend their study internationally. Dr Nick Neave, who carried out the study with Kerry Shields, said: "There are large cultural differences in perceptions of facial hair, and we are hoping to expand on this research by conducting a large-scale study assessing female perceptions of male facial hair in different in as many countries as possible."