Multiple sclerosis (MS) is a condition that affects the central nervous system. This condition may affect over 900,000 people in the United States. It develops as a result of the immune system attacking the protective myelin sheath around nerve cells.

Doctors don’t know the exact cause of MS, but some factors can increase your risk of developing the disease. These include genetics, environmental factors, and the presence of other health conditions, among others.

Read on to learn more about the risk factors of MS.

There are many general risk factors for MS. Most cannot be controlled, but it’s helpful to understand which risk factors might affect you.

Age

MS can occur at any age, but symptoms usually begin between the ages of 20 to 40.

Sex

According to the MS International Federation, women are 2 to 3 times more likely to develop MS than men. This could be explained by differences in the blood-brain barriers in different sexes, according to one 2021 study.

Viruses

Research shows that viral infections could play a role in developing MS. More research is needed, but MS has been linked to:

Vitamin D deficiency

Low levels of vitamin D are associated with a higher risk of MS in white people. This connection isn’t found in Black or Hispanic populations.

Autoimmune conditions

The risk of MS may increase if you already have an autoimmune condition like inflammatory bowel disease, psoriasis, or type 1 diabetes. It’s not clear whether these diseases can cause MS.

Smoking

Cigarettes and cigars increase the risk of MS in both current and former smokers. This effect has also been demonstrated with hookah and secondhand smoke.

Breastfeeding duration

A survey from 2017 found that those who breastfed for at least 15 months had a lower risk of developing MS. It’s not clear how this protective effect might work.

While genetics don’t cause all cases of MS, they’re thought to play an important role.

MS isn’t determined by any single gene, but different combinations of more than 200 genes are thought to increase MS risk.

  • Extended family. A 2021 study found that about 1 in 5 people with MS also have a family member with MS. This includes first-, second-, and third-degree relatives.
  • Immediate family. The Multiple Sclerosis Association of America (MSAA) states that having a close relative like a parent or sibling with MS can increase your risk of developing the condition by about 10 times.
  • Identical twins. The MSAA says when one identical twin has MS, the other has almost a 1 in 3 chance of developing MS, too.
  • Ethnicity. MS was historically thought to be more common in people of European descent. A 2020 study and a separate 2021 review indicate that this view is biased, and MS may be more prevalent in people who identify as Black, Asian, or “Minority Ethnic.”

Some environmental factors have been shown to increase your risk of MS. Examples include:

  • Reduced sunlight exposure. Research indicates that living in a climate with more UVB radiation is associated with a decreased risk of MS. This is especially true during childhood and adolescence.
  • Poor air quality. A 2017 study found that worse air quality increased the risk of MS in children. Specific air pollutants were not identified, but a 2018 study linked nitrogen dioxide and ozone exposure to MS relapses.
  • Organic solvents. Occupational exposure to substances like painting products and varnishes was linked to an increased risk of MS by a 2018 study.

Having obesity, a condition characterized by body mass index (BMI), has been demonstrated to increase the risk of MS in both children and adults.

People ages 20 to 29 with a BMI of at least 30 are more than twice as likely to develop MS than their peers with a BMI between 18.5 and 21.

Some environmental factors are related to MS but haven’t yet been shown to increase your risk. Some of these include:

  • Food allergies. A 2018 study demonstrated that people with food allergies had more MS relapses. Drug, pet, and environmental allergies had no effect on relapses.
  • Heat exposure. Sudden increases in ambient temperature were associated with more clinic visits for MS symptoms in a 2021 study.
  • Heavy metals. A study in 2015 showed a greater MS prevalence in regions with higher soil concentrations of heavy metals like lead and cadmium. There may be an association, but more research is needed to prove a direct cause.
  • Household chemicals. A 2018 survey connected certain chemicals, like weed and insect products, with pediatric-onset MS. The study mentions the results should be interpreted with caution, and more research is required.

A risk factor is different from a cause.

Risk factors for MS are things that increase your chances of developing MS. Causes lead to a definite outcome.

The cause of MS is unknown.

MS is associated with a variety of risk factors. Genetics, environmental factors, and having a high BMI may all be involved. There are also many other risk factors, some still involved in ongoing research.

Doctors are still working to better understand the causes and treatments of MS.