Multiple sclerosis (MS) is a neurological disease — a condition affecting the myelin sheath covering on nerves and within the nervous system. The cause of MS is unknown, but some scientists have suggested that head trauma may be a risk factor for the condition. Such traumatic brain injuries are especially common in motor vehicle accidents: They can happen to drivers, passengers, or pedestrians.

Some research has found connections between concussions (a kind of traumatic brain injury) and a later increased risk of MS. A 2017 Swedish study found evidence that concussions in adolescence were associated with an increased risk of developing MS. The study also found that multiple concussions increased a person’s likelihood of developing MS.

However, research exploring the topic of head injury and the risk of multiple sclerosis has been mixed — some studies have found connections between head trauma and MS and others have not. This article looks at the related studies and shares where MS research stands today.

Can a Car Accident Trigger an Autoimmune Disease?

Multiple sclerosis is considered an autoimmune disease. In MS, the immune system mistakenly attacks the myelin, or protective coating, of nerve fibers in a person’s central nervous system (CNS). This damage to nerve cells causes inflammation and scarring and interrupts communication throughout the brain and spinal cord. This process leads to various MS symptoms, including impaired movement (including trouble walking), fatigue, numbness, muscle spasms, and more.

A head injury can result from an outside force hitting your head or when your brain is shaken inside your head. Such injuries often occur in sports or car accidents, and they can vary in severity. It’s not a scientific fact that a head injury from a car accident could trigger an autoimmune disease. However, there are several theories for how head trauma, like that from a car accident, could contribute to a person developing MS.

Theories on the Connection Between Head Injury and MS

One theory on the connection between head injury and MS is that a head injury could prompt an autoimmune response that impacts the blood-brain barrier. The blood-brain barrier is the border that protects the CNS. If a head injury damages the blood-brain barrier, autoimmune cells that are present in MS may be able to pass that barrier and cause damage, inflammation, and MS symptoms.

There are other theories about how head trauma and brain injuries could be related to the development of MS:

• They could prompt the release of substances that cause inflammation in the brain.
• They could create inflammation in the brain that remains after the brain injury has healed.

It’s also possible that the connection between head injuries and MS is due not to the head injury itself, but to a medication or treatment that people with head injuries commonly receive. More research is needed.

Research on Head Trauma and MS

Several studies have explored possible connections between head trauma and MS, but they’ve had contradictory findings. Differences among research studies have made it difficult for healthcare professionals to make claims about a connection between head trauma and MS. Here’s what researchers know.

Head Injury as a Risk Factor for MS

In one Danish study, researchers considered a group of more than 150,000 people who had been diagnosed with a concussion, brain contusion, or skull fracture and had been hospitalized after the injury.

Researchers looked at how many of these people later developed MS. They found no significant difference in the risk of MS between people who had a history of head injuries and those who didn’t have head injuries. The researchers concluded that head trauma of any severity did not have an effect on a person’s risk for acquiring MS.

Traumatic Injury and MS

In 2013, researchers conducted a systematic review (a study that reviews many other studies) to explore any connections between traumatic injuries and MS. They found no significant association between traumatic injury and the development of MS. However, the studies included in their review used different definitions of traumatic injury, ranging from “accidents and burns” to “head trauma with concussion.” Given those inconsistencies, they couldn’t definitively suggest that head trauma and MS were unrelated, either.

Physical Trauma and Risk of MS

A study published in 2014 explored the topic of physical trauma and the risk of MS. It examined 40 individual research studies. The results found connections between people who had experienced head trauma or other physical trauma as a child, as well as people who had head trauma later in life, and a higher risk of MS as adults. The findings point to a potential connection between head trauma in childhood — and head trauma in general — and an increased risk of developing MS. The authors called for more research on the topic to gather further understanding.

Head Trauma and MS in Genetically Susceptible People

The results of a study published in 2024 in the Journal of Neurology, Neurosurgery and Psychiatry suggest that some people are genetically susceptible to developing MS after a head injury. The findings suggest that people who had a head injury at some point in the past were 30 percent more likely to develop MS. Those who had a head injury within the past five years were 60 percent more likely to develop MS. Like other research, the findings also suggested that having multiple head injuries increases the risk of MS.

Although the results of these studies have limitations (like only drawing from people living in one country) and therefore do not firmly establish a cause-and-effect relationship, the possible link between head injury and MS is worth considering. Additional studies need to be conducted to further understand the connection between head injury and MS.

The research highlights the issue of the potential long-term negative effects of traumatic brain injuries. Thus, making an effort to protect your head from injury — with helmets, other protective sports equipment, and more — is very important.

Other Risk Factors in the Development of Multiple Sclerosis

Multiple sclerosis is neurodegenerative and gets progressively worse over time. Although scientists don’t know the exact cause of MS, they believe it’s influenced by a combination of genetic and environmental factors. These factors are seen as more likely to play a role in MS than injuries from causes like car accidents.

Known common risk features of people who have MS include:

• Certain genetic factors (those passed from parent to child through their DNA)
• Age range of 20 years to 50 years old
• Biological sex of female
• Low vitamin D levels
• History of smoking
• A body mass index (BMI) greater than 30
• History of an Epstein-Barr virus infection

These factors work in different ways — and possibly in combination with each other — to determine a person’s overall risk of developing MS.

Talk to Others Who Understand

On MyMSTeam, the social network for people with multiple sclerosis and their loved ones, more than 218,000 members come together to ask questions, give advice, and share their stories with others who understand life with MS.

Do you have MS and past brain injuries? What have you learned about the connection, and what would you like to share with others about your experience? Share your thoughts in the comments below, or start a conversation by posting on your Activities page.