Multiple sclerosis (MS) is a disease of the central nervous system, which is made up of your brain and spinal cord. People with MS may experience symptoms like memory loss, muscle spasms, loss of balance, eye discomfort, slurred speech, and more.
Multiple sclerosis causes damage to the myelin—the protective layer around your nerve cells, leading disrupted nerve signals to slow down or stop.
In general, having certain gene variants or a family history of MS may raise your risk for developing MS. Some environmental or lifestyle factors—such as smoking tobacco—may also increase your risk for MS.
Theories for What Causes Multiple Sclerosis
Scientists don’t fully understand what causes MS, but they are researching whether it could be an autoimmune disease (when your immune system mistakenly attacks parts of your body), a genetic neurodegenerative disease (a disease caused by a gene mutation that affects nerve cells in the brain), or triggered by viral infections.
MS May Be an Autoimmune Disease
A healthy immune system responds to outside threats with special white blood cells called lymphocytes, which usually identify and attack harmful viruses and other pathogens. With autoimmune diseases, these white blood cells attack the body’s healthy cells by mistake—which can lead to organ or tissue damage.
MS is often called an autoimmune disease, but there isn’t enough research to confirm this. Researchers haven’t been able to identify any specific immune cell that is responsible for MS.
Along with myelin damage, another characteristic MS-related nerve damage is axonal injury—tearing of the nerve connections (axons) in the brain. This type of injury can’t be explained by an autoimmune response.
Even if MS has an autoimmune cause, we still don’t know why many such conditions develop. In general, autoimmune conditions may arise from a combination of factors, including genetics, your medical history, and your lifestyle and environment.
MS May Be From Inflammation Related to Infections
Some researchers are studying whether MS could be due to an immune response to viral or bacterial infections, leading to inflammation. In particular, there may be a correlation between developing MS and a history of Epstein-Barr virus (EBV). EBV is a very common herpes virus that causes mono (mononucleosis or the “kissing disease”), which is transmitted from person to person through saliva.
In a 2022 observational study published in Science, researchers looked at 10 million young adults in the U.S. military. During their military service, about 900 people were diagnosed with MS—their risk for developing it increased by 32 times after contracting EBV.
That said, getting mono does not necessarily mean you’ll develop MS. Even though about 95% of adults eventually get EBV, very few of them develop MS. EBV may be one trigger among several, and researchers suspect the disease may develop due to other factors, associated with genetics or your environment.
Researchers are also looking at the connection of MS to other viral infections, like measles (a vaccine-preventable viral disease), human herpesvirus-6, and chickenpox, along with Chlamydia pneumoniae—a non-sexually transmitted bacterial infection that can cause pneumonia.
Vaccines for Measles-Mumps-Rubella (MMR) and Chickenpox
The CDC recommends the combination MMR vaccine, which protects against measles, mumps, and rubella—three different viral diseases. Two doses—administered at least 28 days apart—are recommended for children and students attending higher education institutions. Adults who are born in 1957 or after should get at least one dose if they haven’t been vaccinated as children.
Instead of the MMR vaccine, children can get the MMR-varicella vaccine (MMRV), which also protects against chickenpox. MMRV is administered in two doses, three months apart.
Alternatively, the CDC recommends the chickenpox vaccine, which is typically administered in two doses, three years apart for children.
MS May Be a Genetic Nerve Disease
Another theory is that the cause of MS may be genetic—one that’s unrelated to an immune response. Scientists are studying certain genetic variants (genetic polymorphisms) that tend to be more common in people who develop MS.
Is Multiple Sclerosis Hereditary?
Multiple sclerosis is not considered a hereditary disease—it doesn’t get passed down in families from generation to generation. But there may be some genetic risk—you may have a higher risk for MS if your family member has the condition.
For the general population, the risk of developing MS is about 0.1% (or 1 in 1,000). The risk increases to 2% if you have a parent or child with MS and up to 3–5% if you have a sibling or fraternal twin who has the condition. If you have an identical twin with MS, you have about a 25% chance of developing the condition.
Having certain genetic variants likely contribute to your risk for MS. Researchers have found more than 200 genes that are linked to MS.3 Most of these genetic variants may play a role in your immune system and may be associated with autoimmune diseases such as type 1 diabetes, rheumatoid arthritis, and lupus.
However, there’s no single gene variation that guarantees you will develop MS.
Who Gets Multiple Sclerosis?
About 1 million people in the United States were living with MS in 2017.
Some people are more likely to develop MS than others. Factors that contribute to this include:
- Age: Most people are diagnosed between the ages 20–50.
- Sex: MS is over 3 times more common in people assigned female at birth than people assigned male. This went up from 1.4 times in 1955—though researchers aren’t sure why. People assigned female may also experience symptoms earlier.
- Ethnicity: MS has most commonly been reported in white people of northern European descent, though more recent research suggests that African Americans get MS at a similar rate.165 Black Americans with MS typically start to experience symptoms around age 33, compared to white Americans with MS who start to have symptoms at age 31.
Certain environmental and lifestyle factors can play a role in your likelihood of developing MS. These factors include:
- Geography: Areas with the highest rates of MS are Europe, southern Canada, northern US, New Zealand, and southeast Australia. The rates may increase from southern to northern hemisphere as well.
- Vitamin D: Low vitamin D blood levels may increase the risk of MS. This is supported by historical studies that included mostly white people, as well as a 2018 study of Black and Hispanic people. Your race, ethnicity, or skin tone may affect your vitamin D levels, along with your diet and how much time you spend in the sun. Limited time in the sun—a natural source of vitamin D—may also explain the geographic differences in MS rates.
- Tobacco smoking: This can increase your risk of MS and may be linked to more severe disease. Quitting smoking may slow down the progression of symptoms. However, this risk may not be because of solely taking tobacco, but the act of smoking it. In a case study, people who only chewed tobacco did not have an increased risk of MS.
- Obesity: If you have obesity during childhood or adolescence, you may have an increased risk of developing MS later in life, especially if you are assigned female at birth. Having obesity in early adulthood may also increase your risk for MS.
- Autoimmune conditions: People with conditions like type 1 diabetes, thyroid disease, psoriasis, and inflammatory bowel disease (IBD) may be more likely to have MS.
Researchers are also considering these potential risk factors, but studies show mixed results. There’s not enough evidence to confirm these are linked to MS:
- Environmental allergies
- Household pets
- Heavy metals such as mercury or lead
- Birth month
Studies have found no connection between vaccines and MS risk.
A Quick Review
The exact cause of multiple sclerosis (MS) is unknown. But there are several theories being investigated by researchers, such as whether it is an autoimmune disease or an inflammatory response after an infection, like the Epstein-Barr virus. A third possibility is MS may be a genetic disease that’s neither autoimmune nor related to an infection. A combination of genetics and environmental and lifestyle factors can raise your risk for MS.
These are all theories, and there’s no way to predict if someone will develop MS. Researchers are continuing to study these theories and develop treatments for MS.
Visit your healthcare provider if you are experiencing any symptoms that affect your nervous system. They can provide a diagnosis and treatments depending on your diagnosis.