Even if the cases of multiple sclerosis are not known for sure, there are a number of factors that are believed to cause this illness. Mainly, it is believed that MS is caused by a combination of environmental, genetic and infectious factors.

Though MS  cannot be seen as a hereditary disease,  the risk of acquiring MS is higher in the relatives of a person who already was diagnosed with this disease, especially parents, siblings and children. Number show a 20% recurrence rate in families.

Environmental factors are also believed to cause MS. It has been proven that people who life farther from the equator have more chances of acquiring the disease, and the disease has a lower rate of occurrence in tropical countries. It is believed that this happens because exposure to  sun makes the body secrete more vitamin D, which has been proven to be in lower than usual doses in people with MS.

A number of microbes were proposed as potential infectious triggers for MS. However, none was directly linked to the disease. There are also a number of viruses like human hepatitis virus that is believed to increase the risk of developing MS in adulthood if infection occurs during childhood. Rubella measles and mumps are also related to MS.