Human hair can be cut and arranged in a variety of styles, and in modern times is done so almost exclusively for aesthetic purposes. However, medieval hairstyles (including male facial hair) varied greatly, depending on culture and time period. Identifying hairstyles remains one of the best methods for roughly dating statuary and other visual art. Certain hairstyles are more-or-less unique to certain cultures, such as the 11th century Norman practice of shaving the back of the head.
Some hairstyles were based on gender, and in much of medieval Europe it was considered immodest for a woman to have her hair exposed or unbound. Troubadours, for example, made much of a lady's unbound hair as an incitement to passion. Other hairstyles were influenced by religion. A monk's tonsure (shaving only the top of the head) was a clearly identifiable mark of his vows. Under their wimples, nuns had extremely short hair as a sign of modesty, especially for the medieval period.
Hair itself can cause serious health concerns if not maintained properly, especially has it can harbour vermin such as lice or fleas. Diseased people sometimes had their heads shaved in an attempt to control sickness. Unwashed hair which is allowed to grow will often form thick matted coils known as dreadlocks (modern dreadlocks achieve this look through cosmetic effort rather than dirt and oil).
False hair was used extensively in some Mediterranean cultures, particularly medieval Byzantine, at least among the upper classes, part of the elaborate cosmetics worn at important events. The common use of wigs was not a feature of western European culture until the Renaissance, although false braids appear in the Middle Ages, including a headdress with false braids at the Museum of London. Most wigs are made from human hair, not animal hair as is popularly believed.
Animal hair, was however, commonly used in many things. Horsehair was often collected and turned into fabric, string, or used as decoration, particularly on helmets, as was [camel]] hair in warmer climes.
Animal hair which grows short and dense is called fur,and a whole skin with the fur still on his called a pelt. A skin with little hair was usually called a hide. In heraldry, various background patterns are linked to animal furs, e.g. ermine. These are regarded as tinctures.
Hairstyles in the SCA
In the SCA, hairstyles are generally modern, since the re-enactors have to go back to their mundane lives after an event. If you see a person in an authentic medieval hairstyle (especially something extreme like the semi-skinhead Norman forelock or a braided Viking beard), be impressed.