What Causes MS?
The cause of MS is still not known.
Both genetic and environmental factors are important, but how they interact to cause episodes of localised inflammation in the central nervous system is not clear.
MS is widely regarded as an autoimmune disease where the body produces a misdirected immune response, attacking its own tissue — in this case, the myelin sheath that protects the axons. However, evidence for autoimmunity remains indirect, and MS has different features from other (less common) inflammatory CNS diseases that have been shown to be autoimmune.
It has long been suspected that MS is triggered by a reaction to a virus hidden in the CNS or the immune system, but this theory has also not been proven.