Halo extensions use an invisible wire to attach the extension to your natural hair. The wire is hidden by your hair and is not visible when you are wearing the extensions. Many people worry that the invisible wire will hurt their head or scalp, but this is not usually the case. The wire is very thin and flexible, so it should not cause any discomfort. If you do experience any pain or irritation, you can try adjusting the wire or wearing the halo extensions for a shorter period of time. In most cases, halo extensions are safe and will not cause any damage to your scalp or hair.