What Causes MS?
While the exact cause of MS is unknown, most researchers believe that the damage to myelin results from an abnormal response by the body's immune system. Normally, the immune system defends the body against foreign invaders such as viruses or bacteria. In autoimmune diseases, the body attacks its own tissue. MS is probably an autoimmune disease in which myelin is the major target of an immune attack.
Scientists do not yet know what might cause the immune system to do this. Most agree that several factors are involved, including something in the person's genetic make-up coupled with exposure to something in the outside world, possibly exposure to a common virus or bacterium.