When you have multiple sclerosis (MS), your body’s immune system attacks your central nervous system. This causes inflammation that damages the protective myelin sheath that normally covers the nerve fibers in the brain, spinal cord, and optic nerve, as well as the nerve fibers themselves, according to the National Multiple Sclerosis Society (NMSS).

But no one knows exactly what triggers the immune system to attack the central nervous system. Most experts believe it occurs when a person with a genetic predisposition to MS is exposed to certain environmental conditions, such as a low vitamin D level, smoking, or the Epstein-Barr virus, notes the NMSS.

Since it isn’t known exactly what causes MS, physicians can’t foresee with certainty who will develop the disease, but they do know there are some things that may put you at higher risk.

Genetic Differences Are a Contributing Cause

While small differences in genes are known to contribute to the development of MS, determining exactly what role they play is complicated, says Farrah Mateen, MD, PhD, an associate professor of neurology at Harvard Medical School and neurologist at Massachusetts General Hospital in Boston. There are about 200 genes that each play a small role in increasing your risk of developing MS, according to the NMSS.

And even people with certain predisposing genetic variants may never get MS. In the general population, the risk of developing MS is about 1 in 750 to 1,000. Ariele Greenfield, MD, a neurologist, neuroimmunologist, and researcher at Sutter Health’s Palo Alto Medical Foundation in California, says the strongest genetic risk factors for MS increase a person’s risk by tenfold. In other words, the risk goes from approximately 0.1 percent to 1 percent if you have these risk factors, which is still very low.

What About Family History?

MS isn't an inherited disease, which means families don’t pass it from one generation to the next. However, you can inherit genes that put you at greater risk of developing MS, according to the NMSS.

If you have an identical twin who has MS, you still only have about a 25 percent of developing the disease. The risk also increases when you have other close relatives (parents, siblings, and children) who have MS, but significantly less than in identical twins.

“There’s an increase, but not a guarantee,” of developing MS when a family member has it, Dr. Greenfield says.

Gender and the Risk of Developing MS

Women are 2 to 3 times more likely than men to be diagnosed with relapsing-remitting MS, the most common type of MS, according to the NMSS.

But equal numbers of women and men are affected by primary-progressive MS, a less common type — or possibly stage — of MS associated with more disability.

Women’s greater susceptibility to MS overall is thought to be associated with hormonal changes, Dr. Mateen says.

A number of studies have found that a large proportion of men with MS have low testosterone levels, and a study published in the journal Multiple Sclerosis found an association between low testosterone levels early in the course of MS and more significant declines in cognitive (thinking) function over time.

Other Possible Contributing Causes of MS

There are a number of other factors that are associated with an increased risk for developing multiple sclerosis, although whether any of them are causative is unknown.

Smoking

Smokers and people who are exposed to secondhand smoke have an increased risk of developing MS, according to the NMSS.

A meta-analysis published in March 2016 in the journal PeerJ found that smoking appears to raise the risk of MS more in men than in women, and that current smoking is more dangerous than past smoking.

Low Levels of Vitamin D

A growing body of evidence, including a study published in October 2017 in the journal Neurology, suggests that vitamin D deficiency may increase a person’s risk of developing multiple sclerosis.

In response to such studies, many doctors have begun recommending vitamin D supplements for people who have MS, particularly for those who are vitamin D deficient.

Geographic Location

People who live in more temperate climates — like Europe, southern Canada, and the United States — have a slightly higher risk of MS than those who live closer to the equator, Greenfield says.

Researchers have speculated that this higher risk may be related to less sun exposure in these areas during the colder months and consequently lower levels of vitamin D in the body, according to the NMSS.

Obesity

Studies have shown that obesity in childhood and adolescence, particularly in girls, increased the risk of developing MS at a later age. Other studies have shown that obesity in early adulthood may also raise your risk of developing MS.

Having an Autoimmune Condition

Your risk of developing MS increases slightly if you have other autoimmune disorders such as thyroid disease, pernicious anemia, psoriasis, type 1 diabetes, or inflammatory bowel disease, according to the Mayo Clinic.

Mateen says that while these other conditions don’t cause MS, if you have one autoimmune disease, you have a higher risk of getting a second one, and MS is generally considered an autoimmune disease.

Epstein-Barr Virus

Research has suggested that previous infection with the Epstein-Barr virus (EBV, which causes mononucleosis) is linked to a higher risk of developing MS.

Concussion in Adolescence

In a study published online in October 2017 in Annals of Neurology, researchers in Sweden found that concussion (brain injury) between the ages of 11 and 20 is associated with a higher risk of MS — and individuals who have had more than one concussion have an even higher risk of developing MS than those who have only had one.

While there’s more to be learned about the connection between MS and concussion, the researchers commented that their results emphasized the importance of protecting young people from head injuries.

Race

White people, particularly those of Northern European descent, are at highest risk of developing MS, according to the Mayo Clinic. People of Asian, African, or Native American descent have the lowest risk.

Age

Most people are diagnosed with MS between age 20 and 50, but children and older adults can also develop the disease, according to the NMSS.

Living Near Major Roads

A large study published in January 2020 in the journal Environmental Health found that living near major roads was linked with higher incidence of multiple sclerosis and other neurological disorders.

While further research is needed, the researchers believe air pollution may play a role.

Living near green spaces, however, was found to have some protective effects against MS and the other disorders.

Can You Prevent Your Family Members From Getting MS?

Mateen is often asked by patients if their family members are at greater risk for MS and what they can do to reduce their chances of getting it. Unfortunately, she says, there isn’t a lot you can do to prevent the disease.

“With MS, there isn’t a lot to monitor or evidence that if you change your diet or lower stress or exercise regularly you have less chance of developing it,” she says.

But she does have some advice for family members of persons with MS:

If you have a symptom that might be caused by MS, get it checked out.
Avoid smoking and secondhand smoke.
Try to maintain a healthy weight and make sure you're getting enough vitamin D.

“People should stay mentally and physically active so if someone does get MS, they will have greater physical and mental reserves to deal with it,” Mateen says.

Resources We Love

National Multiple Sclerosis Society

The National Multiple Sclerosis Society is a nonprofit organization that aims to find a cure for MS. It also provides information about symptoms, diagnosis, treatment, resources, and support for MS.

Mayo Clinic

The Mayo Clinic is a nonprofit organization that specializes in clinical practice, education, and research. Its website offers information about the symptoms, causes, risk factors, complications, diagnosis, and treatment of MS.

Editorial Sources and Fact-Checking

Definition of MS. National Multiple Sclerosis Society.
What Causes MS? National Multiple Sclerosis Society.
Primary Progressive MS (PPMS). National Multiple Sclerosis Society.
Bove R, Musallam A, Healy BC, et al. Low Testosterone Is Associated With Disability in Men With Multiple Sclerosis. Multiple Sclerosis. April 7, 2014.
Unhealthy Habits. National Multiple Sclerosis Society.
Zhang P, Wang R, Li Z, et al. The Risk of Smoking on Multiple Sclerosis: A Meta-Analysis Based on 20,626 Cases From Case-Control and Cohort Studies. PeerJ. March 15, 2016.
Munger KL, Hongell K, Aivo J, et al. 25-Hydroxyvitamin D Deficiency and Risk of MS Among Women in the Finnish Maternity Cohort. Neurology. October 10, 2017.
Multiple Sclerosis. Mayo Clinic. June 12, 2020.
Montgomery S, Hiyoshi A, Burkill S, et al. Concussion in Adolescence and Risk of Multiple Sclerosis. Annals of Neurology. October 2017.
Who Gets MS? National Multiple Sclerosis Society.
Yuchi W, Sbihi H, Davies H, et al. Road Proximity, Air Pollution, Noise, Green Space and Neurologic Disease Incidence: A Population-Based Cohort Study. Environmental Health. January 21, 2020.

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