The cause of most cases of Parkinson’s disease is unknown. Although researchers have established that both hereditary and environmental factors influence a person’s risk of developing Parkinson’s, for the most part, they don’t know why some people get the disease and others don’t. Most scientists believe Parkinson’s is most likely caused by a combination of inherited and environmental factors.

Age is the most important factor in the development of parkinsonism (a term referring to several neurological conditions with movement issues, including Parkinson’s disease). Parkinson’s usually develops after age 60, though it starts before 50 for about 5 percent to 10 percent of people, according to the National Institute on Aging. A 2022 study found that in North America, risk increases with age for those 65 and older. Only about 4 percent of cases are diagnosed before age 50. Rarely, Parkinson’s has been diagnosed in people as young as 18.

Parkinsonism With Known Causes

In about 10 percent to 15 percent of cases, Parkinson’s disease is entirely due to genetics. People with a history of family Parkinson’s can ask their doctor for a genetic test to see if they have a genetic mutation that leads to developing the condition.

Certain medications, including antipsychotic drugs, can cause Parkinson’s symptoms as a side effect. Drug-induced parkinsonism is a common cause of parkinsonism after Parkinson’s disease.

Vascular parkinsonism is caused by small strokes in the brain where blood vessels have become blocked. High blood pressure, high blood cholesterol, type 2 diabetes, and heart disease can contribute to the development of vascular parkinsonism.

Risk Factors for Parkinson’s Disease

It’s important to note that although science is good at finding correlations — apparent relationships — between factors and disease, correlation doesn’t prove that the factor causes the disease. Many risk factors for Parkinson’s have been identified and are being studied, but none have been pinpointed as the cause of Parkinson’s.

About 1 percent of the global population over age 60 or older has a form of Parkinson’s. Any random individual 60 or older has a roughly 1 percent chance of developing Parkinson’s. The factors discussed below raise or lower this risk.

Hereditary Factors

The vast majority of people with parkinsonism have no family history of Parkinson’s but may have genetic factors that make them more likely to develop the disease if environmental factors are also present. For instance, certain genes may make it harder for a person to clear toxins from the brain after exposure. Researchers continue to try to better understand the hereditary predisposition for Parkinson’s.

Men are more likely than women to develop Parkinson’s, according to the Parkinson’s Foundation. People with Parkinson’s may experience symptoms of the condition in different ways.

Ethnicity also may have an influence. A study of nearly 600 newly diagnosed cases of Parkinson’s in California found the highest rate of incidence among Hispanic people, followed by non-Hispanic white, Asian, and Black people, in that order.

Environmental Factors

Researchers looking into causes of Parkinson’s have found links with several environmental factors, including pesticides, traumatic brain injury (TBI), diet, and air pollution.

Pesticides

Several studies show a strong link between exposure to pesticides and an increased risk of parkinsonism. The class of pesticides most often linked to Parkinson’s is organochlorine insecticides, which include DDT and dieldrin. Although these substances were banned in the 1970s and ’80s, they remain in the ground and water for many years and often enter the food chain.

Researchers have linked rotenone, paraquat, trifluralin, and permethrin — pesticides currently in use — with a higher risk of Parkinson’s. According to the National Institute of Environmental Health Sciences, people who reported using rotenone or paraquat (both are restricted in the U.S.) were 2.5 times more likely to develop Parkinson’s than those who did not. Risk was reduced by wearing chemical-resistant gloves, washing hands, and using other safety procedures. In some studies, farmers have been found to have higher rates of Parkinson’s than those in other professions, likely due to pesticide exposure.

Traumatic Brain Injury

Multiple studies have found a correlation between traumatic brain injury and later development of Parkinson’s. A large-scale, 12-year study evaluated the medical records of 325,870 military veterans, half of whom had experienced TBI. None had been diagnosed with Parkinson’s. At the end of the study, 1,462 of the veterans had been diagnosed with parkinsonism, including 949 who’d had a traumatic brain injury. Those who had experienced mild TBIs were 56 percent more likely to develop Parkinson’s within the next 12 years. Moderate to severe TBI increased the risk of developing Parkinson’s by 83 percent.

Diet

Research is underway to better understand possible links between diet and Parkinson’s risk. Scientists are pursuing theories that Parkinson’s may be linked to factors such as:

• Vitamin D deficiency
• Vitamin B12 deficiency
• Diets high in saturated (animal-based) fat and low in polyunsaturated (mostly plant-based) fat

Air Pollution

Ongoing studies are examining the role of air pollution in potentially raising the risk of Parkinson’s.

Talk With Others Who Understand

On MyParkinsonsTeam, the social network for people with Parkinson’s disease and their loved ones, more than 105,000 members come together to ask questions, give advice, and share their stories with others who understand life with Parkinson’s disease.

Do you have questions about what causes Parkinson’s disease? Have you and your doctor discussed your risk factors? Share your experience in the comments below, or start a conversation by posting on your Activities page.