The NY Times reports:
The answers, which were published in the Journal of Evolutionary Biology, varied depending on what the woman was looking for. Overall, the women said the sexiest men were those sporting heavy stubble, followed by short stubble. Men with full beards and clean-shaven men were rated the lowest on the overall sexiness scale.
What kind of man is most attractive to a woman looking for a short-term fling or one-night stand? Men with light stubble won that contest, closely followed by men with heavier stubble, suggesting that the scruffy look appeals to women looking for fun, but not commitment.
But when it came to choosing a long-term partner, a guy with whom a woman could have babies or settle in for the duration, the more facial hair the better. Men with heavy stubble and full beards were the clear winners on this question, suggesting that men who are ready to commit might do better if they shave less often.