How Do You Get Multiple Sclerosis Known Risk Factors?

Multiple sclerosis is not caused by one thing you did or didn’t do. It develops when a person’s immune system attacks the protective coating around nerves in the brain and spinal cord, and the risk of that happening comes from a mix of genetics, environment, infections, and lifestyle factors that build on each other over years.

No single risk factor causes MS on its own. Most people who carry known risk factors never develop the disease. Researchers describe MS as a complex condition where several factors likely need to line up before symptoms appear.

What Is Actually Happening in Multiple Sclerosis?

MS is an autoimmune disease of the central nervous system. The immune system, which normally defends against infections, mistakenly targets myelin — the fatty sheath that insulates nerve fibers. When myelin is damaged, nerve signals slow down or get disrupted.

That disruption produces the symptoms people recognize: numbness, vision problems, balance issues, fatigue, and muscle weakness. Symptoms vary widely because lesions can form in the brain, spinal cord, or optic nerves, and the location of damage determines what a person feels.

What triggers the immune system to turn on myelin in the first place is still not fully understood. What researchers have identified is a set of factors that raise the odds of developing MS. These are called risk factors, and they are not the same as causes. A risk factor shifts probability. It does not determine outcome.

How Do You Get Multiple Sclerosis Known Risk Factors?

Genetics is the strongest single contributor to MS risk. More than 200 genetic variants have been linked to the disease, and most of them involve genes that regulate immune function. The most studied is HLA-DRB1*15:01, a variant in the human leukocyte antigen system that plays a central role in how the immune system recognizes threats.

Having this variant raises risk. It does not guarantee MS. Even identical twins — who share all their genes — are not both affected in most cases. When one identical twin has MS, the other develops it only some of the time, which tells researchers that genetics alone cannot explain the disease.

This is where environment comes in. Genes set the stage. Environmental exposures appear to pull the trigger.

Why Does Where You Live Matter?

MS is more common in countries farther from the equator. People living in northern Europe, Canada, and the northern United States develop MS at higher rates than people living near the equator. This pattern has been recognized for decades and is one of the most consistent findings in MS research.

Researchers believe lower sunlight exposure plays a role. Sunlight helps the body produce vitamin D, and vitamin D helps regulate immune function. Lower vitamin D levels are consistently found in people with MS, though whether low vitamin D contributes to the disease or results from it remains debated.

Migration studies add another layer. People who move from a high-risk region to a low-risk region before adolescence tend to take on the lower risk of their new location. Those who move later in life tend to keep the risk of where they grew up. This pattern suggests that early-life environmental exposure shapes MS risk significantly.

What Role Does Vitamin D Play?

Vitamin D deficiency is one of the most studied environmental factors in MS. Research published in journals such as Neurology and JAMA Neurology has found that low vitamin D levels are associated with a higher risk of developing MS and, in some studies, with more disease activity in people who already have it.

Association is not the same as causation. It remains unclear whether low vitamin D directly increases MS risk or is a marker for something else, such as reduced sun exposure or genetic differences in vitamin D processing.

Clinical trials testing whether vitamin D supplements reduce MS risk or slow disease progression have produced mixed results. Some show modest effects on certain markers. Others show no significant benefit. No major trial has confirmed that taking vitamin D prevents MS in healthy people.

What is clear: vitamin D matters for general health, and low levels are common in northern latitudes. Standard clinical guidance recommends maintaining adequate vitamin D intake through diet and supplements when needed, though specific dosing for MS prevention has not been established.

Can a Virus Trigger Multiple Sclerosis?

Epstein-Barr virus (EBV) is the strongest infectious risk factor linked to MS. EBV is extremely common — most adults worldwide carry it — and it causes mononucleosis in some people. Nearly everyone with MS has evidence of prior EBV infection, compared with roughly 90 to 95 percent of the general adult population.

A large study published in Science in 2022 followed millions of U.S. military personnel and found that EBV infection was associated with a substantially increased risk of later developing MS. This was a significant finding because the study tracked people before and after infection, strengthening the case for EBV as a contributing factor.

But EBV alone cannot explain MS. If it did, nearly everyone would have MS, since nearly everyone has had EBV. Something else must be involved — genetics, timing of infection, immune response differences, or additional environmental factors.

Other infections have been investigated as possible triggers, but none has shown the consistent link that EBV has.

Does Smoking Raise Your Risk?

Smoking is an established risk factor for MS. Multiple studies have found that smokers are more likely to develop MS than nonsmokers, and the risk appears to increase with the number of years smoked. Smoking also appears to accelerate disease progression in people who already have MS.

Secondhand smoke exposure has also been linked to increased MS risk in some studies, though the evidence is less consistent.

The mechanism is not fully understood, but smoking is known to promote inflammation and affect immune regulation, both of which are relevant to autoimmune disease. Smoking is also linked to many other health conditions, so the MS connection is one of several reasons it matters.

Can Obesity or Childhood Factors Affect Risk?

Childhood and adolescent obesity is linked to a higher risk of MS. Several large studies, including research published in PLOS Medicine, have found that higher body mass index during childhood and adolescence is associated with increased MS risk later in life. The association is stronger in girls than boys in some studies.

The reasons are not entirely clear, but excess body fat promotes chronic low-grade inflammation, which may influence autoimmune processes. Obesity also affects vitamin D levels, since vitamin D is stored in fat tissue and may be less available for use by the body.

Other early-life factors have been studied, including birth month, maternal health during pregnancy, and breastfeeding. Some studies suggest that breastfeeding during infancy may be associated with lower MS risk, but findings are not consistent across all research.

Are There Factors That Lower Risk?

Some factors appear to be associated with lower MS risk. Higher vitamin D levels, adequate sun exposure, and not smoking are consistently linked to lower risk in observational studies. Whether these factors actively protect against MS or simply reflect other underlying differences is not fully established.

Some research suggests that certain infections in childhood — particularly those that train the developing immune system — may reduce autoimmune risk later. This idea, sometimes called the hygiene hypothesis, has been explored in MS research but remains an area of active investigation rather than a confirmed mechanism.

No lifestyle change has been proven to prevent MS in people at risk. That is an important distinction. Reducing known risk factors may be reasonable for general health, but no specific intervention has been shown in clinical trials to prevent MS.

Who Is Most Likely to Develop MS?

MS is more common in women than men, typically by a ratio of about 2 to 1 or 3 to 1 depending on the population studied. It is most often diagnosed between ages 20 and 40, though it can appear at any age.

Certain populations have higher rates than others. People of Northern European descent have higher MS rates than people of African, Asian, or Hispanic descent, though MS occurs in all ethnic groups and the gap is not absolute.

Family history matters. Having a parent or sibling with MS raises a person’s risk compared with someone with no family history, but the absolute increase is modest for most people. The vast majority of people with a family history of MS never develop the disease.

What Does Not Cause Multiple Sclerosis?

Several claims about MS causes circulate online and in conversation. Most are not supported by evidence.

• Stress alone does not cause MS, though stress can worsen symptoms in people who have it.
• Vaccines have not been shown to cause MS in large population studies.
• Diet alone has not been shown to cause or prevent MS.
• Mercury, aluminum, or other environmental toxins have not been established as causes of MS.
• A specific food allergy or intolerance has not been shown to trigger MS.

When people ask what caused their MS, the honest answer is that no single cause has been identified. The disease likely results from a combination of genetic susceptibility and environmental exposures that interact over time in ways researchers are still working to understand.