Any trip to the drug store will demonstrate that people today spend a lot of effort on their hair. Shampoos, conditioners, straighteners, products that are supposed to add curl, products that are supposed to add body, fill the racks.
Medieval people too were concerned about their hair. Both hair and beards were markers of status and position. If one did not wear one's hair in the latest, most fashionable style, everyone noticed.
Beards were for old, venerable men. The Song of Roland from around 1100, for example, depicts Charlemagne as having a long white beard. Young men, however, rarely grew beards. A knight would not have a beard, because it could get stuck in his chain mail. Both younger and older men normally grew their hair to a little above shoulder length, although the Normans were reputed to shave the backs of their heads. Curly hair was considered very attractive, and the unkind accused elegant men of using curling irons--and thus being feminized.
Indeed, if one looks at a medieval illustration, it may initially be difficult to tell the young men and young women apart, as both have rosy, beardless faces. The real clue (aside from the fact that women's outfits were ankle length, rather than knee length) is that women's hair was typically covered in illustrations.
The Old Testament talks about women covering their hair, and medieval people took this seriously--as the modern Amish still do. A well-bred matron would not go out in public without her wimple, sort of a hood that covered her hair as well as her neck (traditional nuns still wear them). Unmarried girls, however, would show their hair, which was supposed to be golden and curly for true beauty (a sentiment with which modern movies seem to agree). Often a maiden would wear a chaplet or wreath of flowers to set off her hair, which would be at least shoulder-length.
Entering religion, as a priest, monk, or nun, entailed a radical change in one's hair. Nuns had all their hair cut off. A runaway nun would thus be very easy to identify. A monk would receive a tonsure, where the crown of his head was shaved, leaving only a circle of hair.
The image here is a rather fanciful portrait of Saint Bernard of Clairvaux and shows his tonsure. Again, a runaway monk would be easy to spot. The style is reminiscent of male pattern baldness, which it may have been intended to suggest, and required that the monks have the tops of their heads shaved weekly.