It would have totally changed humanity. For as long as we have existed, we would have been covering our hair to protect it. Long leather "hair-sheathes" would probably have been standard, and since the hair could never be cut without hurting yourself, my guess is that most would have their hair tied up so that it couldn't tangle or tear on things. The old would have super long hair.
...Or would there even BE any older people? If your hair starts going away, would you lose enough blood that you would die? Would the only elderly be the ones that never lose their hair?
Also, everyone would be 100% hairier overall. No shaving, face or otherwise.
