The cause of most cases of Parkinson’s disease is unknown. While researchers have established that both hereditary and environmental factors influence a person’s risk for developing Parkinson’s, for the most part, they don’t know why some people get Parkinson’s and some people 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. Parkinson’s is typically diagnosed between the ages of 40 and 70. Risk increases after age 60, with the majority of people diagnosed in their 70s. Only about 4 percent of Parkinson’s disease cases are diagnosed before age 50. Rarely, Parkinson’s has been diagnosed in people as young as 18.

Parkinsonism With Known Causes

In approximately 10 percent to 15 percent of cases, Parkinson’s disease is entirely due to genetics. People with a history of familial Parkinson’s can ask their doctor for a genetic test to determine whether 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 the second-leading 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, diabetes, and heart disease can contribute to the development of vascular parkinsonism.

Read more about different types of Parkinson’s.

Risk Factors for Parkinson’s

It is important to note that while science is good at finding correlations — apparent relationships — between factors and disease, correlation does not 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 population age 60 or older has a form of Parkinson’s. Any random individual 60 or over 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 predispose them for developing Parkinson’s in the presence of other, environmental factors. For instance, certain genes may make it harder for a person to clear toxins from the brain after exposure. Research to better understand hereditary predisposition for Parkinson’s is ongoing.

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

Ethnicity may influence Parkinson’s predisposition. A study of nearly 600 newly diagnosed cases of Parkinson’s in California found the highest rate of incidence among people of Hispanic background, followed by non-Hispanic people of European descent, then people of Asian descent, and finally people of African descent.

Environmental Factors

Several studies show a strong link between exposure to pesticides and an increased risk for developing parkinsonism. The class of pesticides most frequently 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. Rotenone, paraquat, trifluralin, and permethrin are pesticides currently in use that have been associated with a higher risk for Parkinson’s in research. According to the National Institute of Environmental Health Sciences, people who reported using rotenone or paraquat were found to be 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.

Multiple studies have found a correlation between traumatic brain injuries (TBIs) and later development of Parkinson’s. A large-scale, 12-year study evaluated the medical records of more than 325,870 military veterans. Half of the veterans had experienced TBIs. None had been diagnosed with Parkinson’s. At the end of the 12-year study, 1,462 of the veterans had been diagnosed with parkinsonism, with 949 of those having experienced traumatic brain injuries.

Those who had experienced mild TBIs were 56 percent more likely to develop Parkinson’s within the next 12 years. Moderate-to-severe TBIs increased the risk of developing Parkinson’s by 83 percent.

Research is underway to better understand possible links between diet and Parkinson’s risk. Scientists are pursuing theories that vitamin D or vitamin B12 deficiency or diets high in saturated (animal-based) fat and low in polyunsaturated (mostly plant-based) fat may contribute to the development of Parkinson’s.

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

Condition Guide

• Parkinson’s Disease and Parkinsonism — An Overview
• Parkinson’s — The Path to Diagnosis
• Side Effects of Parkinson’s Treatment
• Stages of Parkinson’s
• Symptoms of Parkinson’s
• Treatments for Parkinson’s and Parkinsonism
• Types of Parkinson’s