Are men more attractive clean shaven, with a 5 o'clock shadow, after a few days razor free or with a lumberjack beard?

Research into how men are perceived (by both women and men) is trying to understand how humans see men's masculinity and so called "socio-sexual attributes."

Researchers from the University of New South Wales, Australia took photographs of 10 men when they were clean shaven, at 5 and 10 days without shaving and with a full beard. They then asked 351 women and 177 heterosexual men to evaluate what they thought of the men in various phases of beard growth. Each face was rated for attractiveness, masculinity, health and potential parenting ability.

Women chose men with a heavy 10-day beard as the most attractive and both women and heterosexual men chose men with full beards as the best with perceived parenting skills. Men with light stubble (5 days of growth) got the lowest scores across the board from both men in women in all categories.

According to the researchers concerning 5-day growth "a threshold of density and distribution may be necessary for beards to function as an attractive signal."

Researchers also tested women who were on contraceptive pills and determined that women who were highly fertile and ovulating increased their score of men's masculinity rating compared to women not ovulating. But interestingly, the phase of fertility that women were in had no effect on their impression of a man's attractiveness.

They conclude that stubble conveys maturity and manliness, with less aggressiveness implied by a full beard.

The study published in the journal Evolution and Human Behavior can be found here.