Why is my 20 year old scar getting longer and itch?

The cells then unite at the center, attach together and contract to pull the wound shut. This process creates a mechanical stress that activates the itch nerves and tells the spinal cord to scratch. These nerve fibers can also be activated by chemicals secreted by the body, which is how wound healing causes itching. This itching may be due to the healing process. It may also be due in part to some dryness of the skin overlying the scar.