What Causes MS?

While the cause of MS is still not known, research indicates that a combination of several factors may be involved.


It is now generally accepted that MS involves an autoimmune process—an abnormal immune response directed against the central nervous system. The exact antigen, or target, that the immune cells are sensitized to attack remains unknown. In recent years, however, researchers have been able to identify which immune cells are mounting the attack, some of the factors that cause them to attack, and some of the sites, or receptors, on the attacking cells that appear to be attracted to the myelin to begin the destructive process.


Studies have shown that people who are born in an area of the world with a high risk of MS and then move to an area with a lower risk before the age of 15, acquire the risk of their new home. This suggests that exposure to some environmental agent that occurs before puberty may predispose a person to develop MS later on.

MS is known to occur more frequently in areas that are farther from the equator. Some scientists think the reason may have something to do with vitamin D, which the human body produces naturally when the skin is exposed to sunlight. People who live closer to the equator are exposed to greater amounts of sunlight year-round. As a result, they tend to have higher levels of naturally-produced vitamin D, which is thought to have a beneficial impact on immune function and may help protect against autoimmune diseases like MS.

Infectious Agent

Since initial exposure to numerous viruses, bacteria and other microbes occurs during childhood, and since viruses are well recognized as causes of demyelination and inflammation, it is possible that a virus or other infectious agent is the triggering factor in MS.

More than a dozen viruses and bacteria, including measles, canine distemper, human herpes virus-6, Epstein-Barr, and Chlamydia pneumonia have been or are being investigated to determine if they are involved in the development of MS, but so far none has been definitively proven to trigger MS.


While MS is not hereditary in a strict sense, having a first-degree relative such as a parent or sibling with MS increases an individual’s risk of developing the disease. There are studies that show there is a higher prevalence of certain genes in populations with higher rates of MS. Common genetic factors have also been found in some families where there is more than one person with MS.

Some researchers theorize that MS develops because a person is born with a genetic predisposition to react to some environmental agent that, upon exposure, triggers an autoimmune response. The process may require one or several triggers, so that MS may occur only if a series of multiple factors and circumstances are all in place.

Sophisticated new techniques for identifying genes may help answer questions about the role of genes in the development of MS.

What is MS?