For humans, haircut, hairstyle, or hairdo normally describe cutting or styling head hair. Unlike other animals, human beings of many cultures cut their hair, rather than letting it grow naturally. Hair styles are often used to signal cultural, social, and ethnic identity. Men and women naturally have the same hair but generally hairstyles conform to cultural standards of gender. Hair styles in both men and women also vary with current fashion trends, and are often used to determine social status.
There is a thriving world market in cut human hair of sufficient length for wig manufacture and for the production of training for student hairdressers and barbers. In less developed countries, selling one's hair can be a significant source of income — depending on length, thickness, condition, and colour, wig makers have been known to pay as much as US$40 for a head of hair. In the United States, cut hair of at least 10 inches (25 cm) length may be donated to a charity, such as Locks of Love.