ALS has no known cause. Many factors may play a role in whether or not someone develops ALS. These include genetics, sex, race, exposure to toxins, and other environmental factors.

Amyotrophic lateral sclerosis (ALS) is a neurological disorder that affects motor neurons — nerve cells that control muscle movement and breathing.

In ALS, motor neurons stop working and begin to die. This leads to muscle weakening, loss, and eventual paralysis.

The exact cause of ALS remains unknown. However, scientists have identified several potential risk factors.

Experts estimate up to 10% of ALS diagnoses are familial. This means that two or more people in a family have received an ALS diagnosis.

Scientists have identified several gene mutations that contribute to ALS. These include mutations in the following genes:

  • C9ORF72
  • SOD1
  • FUS

The ALS Association notes that mutations in these genes are found in up to 70% of familial ALS diagnoses.

Genes associated with ALS are usually linked to familial inheritance. But people with sporadic (nonfamilial) ALS may have genetic mutations triggered by environmental damage.

Males are slightly more likely to develop ALS. They’re also more likely to be younger at diagnosis.

However, a 2024 review notes that this evens out with age, with older females having a similar prevalence of ALS to males.

ALS can affect people of all races and ethnicities. However, it’s much more common in white people.

In a 2023 analysis of U.S. data, ALS was almost twice as prevalent in white people (6.9 cases per 100,000 people) than in Black people (3.6 cases per 100,000).

Smoking has several negative health effects on the body. Research also links it to an increased risk of ALS.

A 2024 meta-analysis found that there was a positive association between smoking and ALS risk. The risk was higher for current smokers.

Research has identified military service as a potential risk factor for ALS.

A 2018 study on ALS prevalence in the United States found that a large proportion of older people with ALS had served in the military at some point.

A 2021 systematic review found that military service was suggestive of increased ALS risk, particularly in veterans of World War II and the Gulf War. Exposure to substances like Agent Orange, heavy metals, chemicals, and head trauma appeared to contribute to risk.

Research links exposure to a variety of environmental toxins to ALS risk. For example, a 2023 meta-analysis found a link between the following types of environmental toxins and a higher risk of ALS:

  • heavy metals, such as lead, mercury, and selenium
  • pesticides, including herbicides and insecticides
  • solvents

A 2022 review also found that exposure to beta-N-methylamino-L-alanine (BMAA), a nonprotein amino acid made by a specific type of bacteria called cyanobacteria, was linked to ALS risk.

The review also noted that exposure to formaldehyde and heavy metals like mercury and manganese may also increase ALS risk.

Head trauma has the potential to cause damage to the central nervous system, which includes the brain and spinal cord. It’s possible that experiencing a head trauma may boost your risk of ALS.

A 2021 meta-analysis found a link between head injury and ALS risk. The risk was higher for people who had had a severe head injury.

A separate 2021 study noted that ALS risk was higher for people who had head injuries 10 years or more before the onset of their ALS symptoms.

A 2019 study linked a higher risk of ALS with exposure to electric shocks or extremely low-frequency magnetic fields above what is typical.

A 2021 study also found that ALS risk was higher in people experiencing severe electrical burns. The highest risk was for electrical burns received after age 30 or electrical burns received 10 years or more before ALS symptoms started.

While more research is needed overall, certain viral infections may contribute to ALS.

One group under investigation is enteroviruses, which includes polioviruses, coxsackieviruses, and others.

Enteroviruses can target motor neurons. Additionally, 25–40% of people who’ve had polio develop post-polio syndrome, which can mimic motor neuron diseases like ALS.

Another viral infection under investigation is HIV. This is due to reports of people with HIV experiencing an ALS-like disease.

Some research has linked excessive exercise to an increased risk of ALS. For example, a 2023 review found a link between strenuous, anaerobic physical activity and ALS risk. However, it also notes that additional research into this topic is needed.

Research links few medical conditions with ALS risk. There’s some limited data to support that stroke or other cerebrovascular injury may increase the risk of ALS.

Some medical conditions are linked to a decreased prevalence of ALS. For example, a 2023 meta-analysis noted lower rates of ALS among people with diabetes, kidney disease, and high BMI.

Early symptoms of ALS

According to the National Institute of Neurological Disorders and Stroke, early symptoms of ALS include:

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There’s currently no known way to prevent ALS.

However, addressing potential ALS risk factors may help lower your risk. This could include quitting smoking or avoiding exposure to pesticides or heavy metals.

There’s little evidence on diet and ALS. However, eating a diet rich in antioxidant and anti-inflammatory foods isn’t only good for your overall health but may help prevent age-related diseases like ALS.

A 2020 review notes that indirect evidence suggests that the following may be protective against ALS, although more research is needed:

Other strategies that are beneficial for overall health but may also help reduce ALS risk include engaging in regular physical activity (that’s not too intense) and finding ways to reduce stress levels.

ALS has no known cause. For some people, ALS is familial and happens due to specific genetic mutations.

Sex and race also play a role in ALS risk, with males and white people at a higher risk. Other potential risk factors for ALS include exposure to environmental toxins, head injuries, and electrical shocks.

There’s currently no way to prevent ALS. Quitting smoking, if you smoke, and reducing exposure to environmental toxins may help lower your risk. Healthy lifestyle choices involving diet, exercise, and stress reduction may also be beneficial.