Demyelination is the term used for a loss of myelin, a substance in the white matter that insulates nerve endings. Myelin helps the nerves receive and interpret messages from the brain at maximum speed. When nerve endings lose this substance they can not function properly, leading to patches of scarring, or ‘sclerosis’, occurring where nerve endings have lost myelin. It is these areas of scarring that give multiple sclerosis its name.

Demyelination is the root cause of the symptoms that people with MS experience. When it occurs the speed at which messages pass along the nerves is slower than normal. Even when the patches of scarring caused by demyelination have healed and re-myelination has occurred, the response time of the nerve endings tends to remain slower.