A study:
Abstract It was predicted that men would emphasize sexually-selected traits, including mustaches, beards, and sideburns, when they have difficulty obtaining spouses.
Using annual data on British beard fashions extending from 18421971, it was found that mustaches, and facial hair in general, are more frequent when there is a good supply of single men of marriageable age. Facial hair fashions, particularly mustaches and beards, were reduced when illegitimacy ratios were high. Regression analyses showed that the relationship between mustache fashion and the marriage market and illegitimacy, respectively, is independent of linear time trend. Results suggest that facial hair is worn to enhance a man's marriage prospects by increasing physical attractiveness and perception of social status. Men shave their mustaches, possibly to convey an impression of trustworthiness, when the marriage market is weak and women might fear sexual exploitation and desertion.