The exact cause of multiple sclerosis (MS) remains unknown, but it is well-established that MS is an autoimmune condition, meaning the body’s immune system mistakenly attacks its own tissues. In MS, this attack targets the central nervous system (CNS), specifically the myelin sheath, a protective covering around nerve fibers in the brain, spinal cord, and optic nerves. This immune response damages the myelin, and sometimes the nerve fibers themselves, causing symptoms such as vision problems, spasticity, muscle stiffness, and muscle weakness.

Although researchers have established that both hereditary and environmental factors influence a person’s risk of developing MS, no one has identified why some people are diagnosed with MS and some aren’t. Most scientists believe MS is most likely caused by a combination of inherited and environmental factors.

Risk Factors for MS

Science is good at finding correlations — or apparent relationships — between factors and disease, but correlation does not prove that the factor causes the disease. While certain genetic and environmental factors may influence who develops MS, more research is needed to understand why some people get MS and others do not.

Genetic Factors

MS doesn’t appear to be directly inherited from parents in any clear genetic pattern. However, having a close family member with MS, such as a parent or sibling, increases a person’s risk.

In the general population, the risk of developing MS is around 0.2 percent. However, for those with a sibling with MS, the risk rises to between 2 percent and 4 percent. For identical twins, the risk is up to 30 percent. Researchers continue to study the genetic factors that may contribute to MS.

Gender and Biological Sex

Women are about three times as likely as men to develop MS, according to Penn Medicine. In general, autoimmune diseases are more prevalent in women than in men — around 80 percent of people with autoimmune disease are women, according to Cureus.

Researchers have found that females’ immune systems may offer stronger protection against infections than males’, according to research in Nature. However, this heightened immune response may also increase susceptibility to autoimmune conditions like MS.

Race and Ethnicity

Ethnicity may influence MS predisposition. A research study from Multiple Sclerosis found that MS “has a strong racial and ethnic component and disproportionately affects whites of European background.” It also found that rates are increasing among African Americans, while Hispanic and Asian people remain less likely to develop MS. Researchers have observed rising diagnoses in specific subgroups, however.

These groups may also experience symptoms differently and vary in the typical age at diagnosis relative to white people. Some ethnic groups, such as the New Zealand Maori and First Nations in Canada, have a low incidence of MS.

Environmental Factors

Researchers have identified a wide range of environmental factors linked to the development of MS. These factors go beyond just the physical environment we live in, like climate or geography, to include lifestyle choices and health factors. ​

Geography

One of the earliest environmental factors identified is geography. MS is more common in regions farther from the equator, while it is very rare in equatorial areas.

Additionally, individuals living farther from the equator tend to experience MS symptoms earlier. If a person moves from a low-risk to a high-risk latitude during childhood, their risk of developing MS increases accordingly. Conversely, moving to a lower-risk area in early life reduces overall risk.

The geographic difference in risk for MS has led researchers to study links between vitamin D and MS. People living closer to the equator, where there is more sunlight year-round, produce more vitamin D through skin exposure.

Studies have established a link between low levels of vitamin D and a higher risk of developing MS. Current research is investigating whether vitamin D supplementation can help prevent MS or benefit those already diagnosed, especially if supplementation begins in childhood.

Some researchers also link geographic risk to diet. Populations in lower-risk areas often live near the ocean and consume more fish, such as salmon, mackerel, herring, and sardines, which are rich in vitamin D as well as omega-3 fatty acids. These nutrients are thought to have anti-inflammatory properties. Diets that are low in saturated fat and high in lean protein and fresh produce have been shown to improve MS symptoms.

Smoking

According to the Multiple Sclerosis Association, women who smoke are 1.6 times more likely to develop MS, and the risk rises with the number of packs per day. Studies also show that MS progresses more rapidly in those who currently smoke compared to those who do not.

Age

Age is a significant risk factor for MS, with most diagnoses occurring between the ages of 20 and 40. MS is less commonly diagnosed in older adults and is rare in children. Pediatric cases make up only about 3 percent to 5 percent of MS.

Viral Infection

Several studies have investigated specific viruses for links with MS. Some scientists believe that common viruses may trigger genetic changes in some people, increasing their risk of developing MS. Viruses under investigation include:

• Epstein-Barr virus (the cause of mononucleosis, or “mono”)
• Varicella-zoster virus (a herpes virus responsible for chickenpox and shingles)
• Human herpesvirus-6 (the cause of roseola)
• Measles virus

Injury

Researchers have found a correlation between head trauma experienced between ages 10 and 20 and an increased risk of developing MS later in life. Individuals who suffered concussions during this period appear more likely to develop MS as adults, with the risk increasing further for those who experienced multiple concussions.

Seasonal Factors

One study in Finland found that people born in the spring had a higher risk of developing MS. Researchers believe that women who were pregnant during the winter may have had lower vitamin D levels because of less sun exposure, which could increase the chances of their children developing MS later in life. Other research supports this idea, showing that low vitamin D levels during pregnancy may raise the risk of MS in children.

Talk to Your Doctor

While the exact causes of multiple sclerosis remain a mystery, it’s clear that many factors — genetics, lifestyle, and environmental influences—can play a role in its development. However, none of these factors fully explain why some people get MS and others do not.

If you’re concerned about your risk for MS or already living with the condition, talking with your health care provider can help you better understand your personal risk factors or how to manage symptoms. They can offer personalized advice, recommend strategies to maintain your health, and guide you in making informed decisions about your care. Staying informed and proactive is key to living well with MS.

Find Your Team

MyMSTeam is the social network for people with multiple sclerosis and their loved ones. On MyMSTeam, more than 215,000 members come together to ask questions, give advice, and share their stories with others who understand life with MS.

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