What Causes MS?

Reviewed by: HU Medical Review Board | Last reviewed: June 2022

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS). MS affects more than 2.3 million people in the world. Much time and effort have gone into determining what causes MS. While there are no clear answers, it appears that a mix of factors working together triggers MS.1,2

Immune response

The most common theory is that MS is caused by an autoimmune response. Autoimmune responses occur when the body’s immune system attacks healthy tissue. In MS, the immune system attacks myelin, the protective cover around nerve cells.2

Myelin damage and inflammation harm a person's nerves. This makes it harder for the nerve cells in their brain and spinal cord to communicate with the rest of their body.3

The exact cause of this autoimmune reaction is still unknown. But experts believe that it may be triggered by a mix of factors including:2,3

  • Environment
  • Genes
  • Infection


Exposure to certain environmental factors may trigger an autoimmune reaction.2


MS is more common in countries that are farther from the equator. This suggests that less exposure to sunlight may play a role in causing MS. Sunlight is needed to make vitamin D. People who don't have enough vitamin D have a greater risk of developing MS.2,3

Also, people who live in northern latitudes (such as Europe and North America) are at higher risk for MS. This may be because these regions have less sunlight overall.2,3


Smoking has been linked to a higher risk of developing MS. This may be because smoking damages myelin. Smoking also has been linked to increased risk of relapse in people with MS.2,3


Obesity in children and teenagers, especially girls, has been linked to increased risk of MS. Some studies have shown that obesity in early adulthood may also raise the risk of MS.2

It is not clear why obesity may increase the risk of developing MS. It might be because obesity changes the immune system's response. More research is needed to know if there is a true link between obesity and MS.2


MS is more common in people who have a family history of the disease. This suggests that there may be a genetic aspect to MS. Scientists have found a number of different genes that increase the risk of developing MS. However, MS is not an inherited disease. It is still not clear how genes contribute to the cause of MS.2


Some evidence suggests that certain infections may trigger the autoimmune response that leads to MS. Studies have found that people with MS were more likely to have antibodies against a number of different viruses. Antibodies are proteins produced by the immune system to fight foreign substances in the body. This suggests that infection with these viruses may play a role in MS development.2-4

Epstein-Barr virus (EBV)

The Epstein-Barr virus (EBV) may be linked to MS. EBV is the virus that causes mononucleosis, or “mono.” Mono is a viral infection that causes fatigue, sore throat, and fever.2,4

There is evidence that suggests a possible link between EBV and MS. However, it has not been proven that EBV is a direct cause of MS. One study found that people who had MS were more likely to have antibodies against EBV. This suggests that the virus may be involved in the development of MS.2,4

Not every person who has EBV will develop MS. In fact, an estimated 95 percent of adults have been infected with EBV, and most will never develop MS. Why EBV may help trigger MS in some people is unclear and is an active area of research.2,4,5

Human herpes virus (HHV-6)

Human herpes virus 6 (HHV-6) is closely related to EBV. Similar to EBV, HHV-6 is a common infection and about 95 percent of adults have been infected with it. Some research has linked HHV-6 to relapse in people with MS. While this link is not definite, it suggests that HHV-6 may play a role in the development of MS.4,6


It is likely that MS is caused by a combination of these factors. For example, someone may be born with a genetic tendency to MS. This person may then be exposed to an environmental trigger or infection that causes the autoimmune response to occur.1-4

Despite all the research that has been done, the exact cause of MS is still unknown. However, there are many treatments available that can help manage the symptoms of MS. If you think you may have MS, see a doctor to get the proper diagnosis and treatment.2

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