The cause of multiple sclerosis is unknown as of 2015, but scientists believe immunologic disorders, genetics, the environment and infections play roles in the development of the immune disorder, according to Healthline. Factors proven not to be triggers for MS include aspartame, heavy metal exposure, pets, physical trauma and allergies.
In multiple sclerosis, the myelin sheath surrounding the nerve is attacked by the immune system, states Healthline, and researchers are unsure as to why this happens. Ongoing research continues to try to determine which part of the immune system is malfunctioning.
The National Multiple Sclerosis Society notes that individuals who live farther from the equator are more likely to be diagnosed with MS than those who live closer to the equator. There appear to be MS "clusters" where people diagnosed with multiple sclerosis live in the same area, leading scientists to search for environmental factors that may be causing a higher diagnosis rate in that area.
Scientists don't believe multiple sclerosis is hereditary, but if one family member is diagnosed with MS, the rest of the family is at a higher risk for also developing MS, the society states. Geneticists theorize that there may be a genetic inheritance that predisposes an individual to environmental conditions that, when exposed, cause the development of MS.
As other viruses also have been proven to attack the myelin sheath, scientists are researching the possibility that MS is caused by a virus, the Society states. Scientists have studied several viruses, such as Epstein-Barr and the herpes virus, but none have been proven to be connected to multiple sclerosis.
Some potential evidence may point to vitamin D deficiency and smoking as triggers in developing MS, Healthline states.