Parkinson's develops when neurons in the brain stop producing enough dopamine

Parkinson's disease happens when cells in a specific part of your brain—the substantia nigra—begin to die or malfunction. These cells normally make dopamine, a chemical messenger that helps control movement. When dopamine levels drop, your brain can't send smooth signals to your muscles, and movement becomes difficult, slow, or shaky. The disease progresses as more of these cells fail over time, though the rate varies widely from person to person.

Scientists do not yet know exactly why these dopamine-producing cells die in some people and not others. Parkinson's is not caused by a single factor. Instead, it appears to result from a combination of genetic predisposition, environmental exposures, and age-related changes in the brain. This is why two people with identical genetics might have very different outcomes, and why someone with no family history can still develop the disease.

Key Takeaways

  • Parkinson's occurs when dopamine-producing neurons in the brain deteriorate, disrupting the signals that control smooth movement.
  • Age is the strongest known risk factor—most people are diagnosed after age 60, though younger-onset cases do occur.
  • Genetics play a role, but having a family member with Parkinson's does not mean you will develop it, and most people with Parkinson's have no family history.
  • Environmental exposures such as pesticides and head injuries may increase risk, but no single exposure causes the disease in everyone exposed.
  • Abnormal protein buildup, particularly alpha-synuclein, appears central to how the disease develops, though researchers are still working to understand why this happens.

Age is the strongest known risk factor

The risk of developing Parkinson's increases sharply with age. Most people receive a diagnosis between ages 60 and 80. The disease is rare before age 50, though it does occur—cases diagnosed before age 50 are sometimes called young-onset Parkinson's. As you age, your cells accumulate damage over decades, and the brain's ability to repair or replace failing dopamine neurons declines.

Why aging itself increases risk is not fully understood. One theory is that the brain's quality-control systems—the mechanisms that normally clear out damaged proteins and dying cells—become less efficient over time. Another is that decades of exposure to environmental stressors, combined with normal wear on cellular machinery, eventually overwhelms the brain's defenses. Age alone does not cause Parkinson's, since many people live into their 80s and 90s without developing it, but it is the single strongest predictor of who will.

Genetics influence risk, but inheritance is complex

About 10 to 15 percent of people with Parkinson's have a close relative—parent, sibling, or child—who also has the disease. Researchers have identified several genes that increase the risk of Parkinson's, including LRRK2, GBA, and SNCA. Inheriting one of these gene variants does not may provide you will develop Parkinson's. Some people carry the mutation their whole lives and never show symptoms, while others develop the disease in their 40s or 50s.

The inheritance pattern is not straightforward. Some forms of Parkinson's follow a pattern where inheriting one copy of a mutated gene raises your risk significantly. Other genetic variants only slightly increase your chances. Most people with Parkinson's—roughly 85 to 90 percent—have no known family history, meaning their disease likely arose from a combination of common genetic variations and environmental factors rather than a single inherited mutation.

Environmental exposures may increase risk

Certain environmental factors have been linked to higher Parkinson's risk, though none directly causes the disease in everyone exposed. Pesticide exposure, particularly in agricultural settings, appears in multiple studies as a risk factor. People who work with or live near pesticides show higher rates of Parkinson's than the general population. The mechanism is not clear, but some pesticides may damage dopamine-producing cells directly or trigger the immune system to attack them.

Head injuries, especially repeated concussions or severe trauma, have also been associated with increased risk. Some research suggests that traumatic brain injury may set off a cascade of damage that eventually leads to Parkinson's years or decades later. Exposure to heavy metals like manganese has been linked to a Parkinson's-like condition in occupational settings, though whether this represents true Parkinson's or a separate disorder remains debated. Other suspected factors include certain solvents and herbicides, though the evidence is less consistent.

Millions of people are exposed to pesticides or experience head injuries without developing Parkinson's. Environmental exposure likely matters most in people who are already genetically predisposed, or whose exposure occurs at a critical time in brain development or aging.

Abnormal protein accumulation appears central to the disease process

Inside the brains of people with Parkinson's, researchers find clumps of a protein called alpha-synuclein. These clumps, known as Lewy bodies, accumulate inside dopamine-producing neurons and appear to interfere with how the cells function. The protein misfolds—twists into an abnormal shape—and then spreads from cell to cell, like a chain reaction. As more neurons become filled with these toxic clumps, the cells eventually die.

Why alpha-synuclein misfolds in some people and not others is still unknown. Genetic mutations in the SNCA gene, which codes for alpha-synuclein, can cause the protein to misfold more easily. But most people with Parkinson's have normal SNCA genes, suggesting that other factors—aging, inflammation, oxidative stress, or environmental triggers—can cause misfolding in anyone. Understanding this process has become a major focus of Parkinson's research, because if scientists can stop or slow the misfolding and accumulation of alpha-synuclein, they might be able to slow or prevent the disease.

Inflammation and immune system changes may contribute

Recent research suggests that neuroinflammation—inflammation inside the brain—plays a role in Parkinson's development. Immune cells in the brain called microglia become overactive in people with Parkinson's and may attack dopamine-producing neurons. Whether this inflammation is a cause of the disease or a consequence of the dying cells is not yet clear, but it appears to accelerate the damage once the process begins.

Some researchers theorize that an environmental trigger—an infection, toxin, or injury—might activate the immune system in a way that damages dopamine neurons in genetically vulnerable people. Others suggest that the accumulation of alpha-synuclein itself triggers immune activation. The relationship between genetics, environment, immune function, and protein misfolding is likely interconnected, with each factor influencing the others.

Frequently Asked Questions

Can you inherit Parkinson's from a parent?

You can inherit a genetic mutation that increases your risk, but inheriting the mutation does not mean you will definitely develop Parkinson's. About 10 to 15 percent of people with Parkinson's have a family history. If a parent has Parkinson's, your risk is higher than the general population, but most people with a family history never develop the disease.

Does pesticide exposure cause Parkinson's?

Pesticide exposure is associated with higher Parkinson's risk, particularly for people who work in agriculture or live in areas with heavy pesticide use. However, exposure does not cause Parkinson's in everyone exposed. The risk appears highest in people who are already genetically predisposed or who experience long-term, high-level exposure.

Is Parkinson's contagious?

No. Parkinson's is not contagious and cannot spread from one person to another through contact, air, or any other means. It is a neurological condition caused by changes in the brain that develop over time within an individual.

Can you get Parkinson's from a head injury?

Repeated head injuries or severe traumatic brain injury have been linked to increased Parkinson's risk in some studies, but a single head injury does not cause Parkinson's. Most people who experience head injuries do not develop the disease. The relationship between head trauma and Parkinson's is still being studied.

Why do some people get Parkinson's and others don't?

Parkinson's results from a combination of factors including age, genetics, environmental exposures, and how your individual brain responds to damage over time. No single factor determines who will develop it. This is why two people with similar genetics and exposures may have very different outcomes.