Demyelination is a process in which the insulating coating (myelin sheath) around the nerve fibers is destroyed, slowing or halting the passage of nerve impulses. The myelin sheath allows nerve impulses to be sent between the brain, the spinal cord, and the nerves in the rest of the body smoothly and quickly.

Demyelination occurs in diseases such as multiple sclerosis (MS), Guillain-Barré syndrome, and chronic inflammatory demyelinating polyneuropathy (CIDP).