Dogs may bite their hair because of their own instincts, or because they like to chew things. They may also be caressing you, just as humans caress others with their hands. Some dogs may bite their hair due to stress or anxiety, or it may be because they have a unique interest in hair.
For example, some dogs like to bite human hair because they like the taste or texture. If your dog chews your hair frequently, you can try to distract him by offering him an alternative, such as a toy or chew treat. If the problem persists, you may also consider consulting a trainer or veterinarian to learn more about the cause of your dog's behavior and find solutions.