Most cases of Parkinson’s disease are idiopathic, meaning the cause is unclear.
It’s widely believed that a person with Parkinson’s may be genetically vulnerable to the disease and that one or more unknown factors in the environment eventually triggers it.
Most of the symptoms of Parkinson’s disease come from the loss of neurons in an area of the brain called the substantia nigra.
Normally, the neurons in this part of the brain make the chemical messenger (neurotransmitter) dopamine, which allows communication with another area of the brain, the corpus striatum.
This communication helps produce smooth, purposeful movement. When the neurons in the substantia nigra die, the resulting loss of communication leads to the motor (movement-related) symptoms of Parkinson’s.
Although the cause of this cell death is unknown, many researchers believe that the cells are killed by clumped proteins called Lewy bodies.
What Are Lewy Bodies?
The affected neurons of people with Parkinson’s disease have been found to contain clumped proteins called Lewy bodies. Researchers aren’t yet sure why Lewy bodies form or what role they play in the disease, but Lewy bodies are believed to be toxic.
Lewy bodies are clumps of a protein called alpha-synuclein. Neurons can’t break down these protein clumps, which may lead to the death of these cells.
Some other theoretical causes of brain cell death in people with Parkinson’s disease include free-radical damage, inflammation, or toxins.
What Are the Risk Factors for Parkinson’s Disease?
Risk factors for Parkinson’s disease include:
Genetics
People with a first-degree relative (parent or sibling) with Parkinson’s are at an increased risk for the disease — possibly as much as 9 percent greater. Genetic risk factors (the presence of certain genes associated with Parkinson’s disease) are more commonly seen in early-onset Parkinson’s.
An estimated 15 to 25 percent of people with Parkinson’s disease have a family history of the disorder, but a condition called familial Parkinson’s, which has a known genetic link, is relatively rare.
Age
The average age of onset is 60, and the incidence rises with advancing age. About 5 to 10 percent of people have “early-onset” or “young-onset” disease, which begins before age 50.
Gender
The prevalence of Parkinson’s is around 1.5 times higher in men than women.
However, some recent studies suggest the gender differences may not be as stark as previously thought.
Pesticide Exposure
Exposure to some pesticides has been shown to raise the risk of developing Parkinson’s.
Problematic chemicals include organochlorine pesticides like DDT, dieldrin, and chlordane. Rotenone and permethrin have also been implicated.
Proximity to golf courses, which utilize a lot of pesticides in course management, has been linked to a greater risk of Parkinson’s Disease. In 2025, a JAMA Network Open study concluded that “the greatest risk of PD was found within 1 to 3 miles of a golf course and risk generally decreased with distance.”
Fungicide and Herbicide Exposure
Exposure to the fungicide maneb or the herbicides 2,4-dichlorophenoxyacetic acid (2,4-D), paraquat, or Agent Orange may raise the risk of Parkinson’s.
A 2023 study into Agent Orange exposure among Vietnam vets found rates of Parkinson’s disease to be 1.31 times higher than normal.
Head Injuries
Recurrent head injuries, particularly repetitive head injuries, may contribute to the development of Parkinson’s in some people. Traumatic brain injuries are also a major risk factor in developing Parkinson’s in later life.
Coffee and Smoking
People who drink coffee or smoke tobacco in moderation have been found to have a lower risk of Parkinson’s disease, due to the phenolic compounds in tobacco and coffee. But while smoking could potentially lower the risk of Parkinson’s disease, it clearly increases the risk of lung cancer and cardiovascular disease, including heart attacks and stroke.
