Is Parkinson's Disease Partly Man-Made? What Science Says About Chemicals, Aging and Prevention

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A Fast-Growing Disease

Parkinson's disease damages brain cells that control movement. It causes tremor, stiffness and slow movement, and it cannot be cured. It is the second most common neurodegenerative disease after Alzheimer's.

A modeling study published in The BMJ in March 2025 projected that 25.2 million people will live with Parkinson's in 2050. That is an increase of 112 percent over 2021. The authors named aging populations as the main reason, since most cases appear after age 60.

The same study stressed that policy can change the outcome. Public health measures that alter risk factors, they wrote, offer hope of slowing the rise.

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Not Just Bad Genes

Only a minority of cases have a clear genetic cause. One large study that offered genetic testing to more than 10,000 Parkinson's patients found that only 13 percent carried a known genetic predisposition.

For most patients, then, genes alone do not explain the disease. Researchers increasingly suspect a mix of inherited vulnerability, environmental exposure and age.

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The Camp Lejeune Case

The strongest evidence so far comes from a U.S. Marine Corps base. For decades, the drinking water at Camp Lejeune in North Carolina was contaminated with industrial solvents. The worst was trichloroethylene, or TCE, a degreasing chemical also used in dry cleaning and manufacturing.

In 2023, VA-backed researchers compared veterans who served at Camp Lejeune between 1975 and 1985 with those at Camp Pendleton in California, where the water was clean. The results were published in JAMA Neurology.

• Of 430 veterans with Parkinson's, 279 had served at Camp Lejeune and 151 at Camp Pendleton.
• Camp Lejeune veterans had a 70 percent higher risk.
• They also showed more early warning signs of the disease, such as tremor and anxiety.
• TCE levels in the water had reached more than 70 times the permitted amount.

Neurologist Ray Dorsey of the University of Rochester called the study solid evidence that exposure to TCE should be limited. He had earlier worked on a small twin study that linked TCE to a sixfold higher risk.

The study compared two groups of veterans. It shows a strong association, not a final proof for every person.

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The Paraquat Debate

Another suspect is paraquat, a widely used weed killer. Dozens of countries have restricted or banned it. An ABC News analysis counted more than 50. Legislative documents and patient groups cite figures above 70.

In the United States, paraquat is still legal, though it is classified as a restricted-use pesticide. The science here is contested.

• The EPA has said its review found no clear link to Parkinson's.
• A 2020 Agricultural Health Study, partly funded by the National Institutes of Health, found no association.
• Critics argue the EPA misread the evidence. Several studies, they say, have found links.
• California regulators said their review so far shows no causal association. A final decision is due by 2029.

Court action and further review at the EPA are ongoing. Legislative records note that this reassessment may take years and does not stop current use.

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Why Proof Is So Hard

Parkinson's rarely has a single cause. It can take decades to develop. Today's patients may have been exposed 30 or 40 years ago, as the Camp Lejeune study shows. Two people can breathe the same air or drink the same water, and only one falls ill.

Counting cases is also tricky. The Michael J. Fox Foundation points out that diagnosis rates differ between countries. In some places stigma leads to underdiagnosis. Definitions of the disease also keep changing as research advances.

This is why many scientists use careful language. Chemicals are a strong suspect, but the field has not yet built the kind of causal proof that exists for smoking and lung cancer.

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Regulation and Open Questions

Regulators are now weighing how to respond. In December 2024, the EPA finalized a rule to ban all uses of TCE. After the change of administration, the agency postponed parts of the rule, saying it intends to reconsider and modify it. In February 2026 it extended a delay for certain exemptions until May 18, 2026.

Supporters of the review say rules must be weighed against costs to industry and the need for workable alternatives. Health advocates want faster action. The debate is likely to continue.

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Outlook

Aging cannot be stopped, but exposure to harmful chemicals can be reduced. Dorsey and fellow neurologist Michael Okun argue in their book "The Parkinson's Plan" that prevention deserves far more attention and funding.

Even researchers who doubt that rapid chemical bans would stop the rise agree on one point. Cleaner water, safer farming practices and better monitoring are sensible steps while the science continues to develop.

For now, the evidence supports a cautious message. Parkinson's is not purely man-made, but man-made factors appear to play a real part, and those are the factors society can influence.

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Sources

1. HealthDay – "Globally, 25.2 Million Projected to Be Living With Parkinson Disease in 2050": https://www.healthday.com/healthpro-news/neurology/globally-252-million-projected-to-be-living-with-parkinson-disease-in-2050
2. Healio – "Projected Parkinson's disease cases worldwide set to hit 25 million by 2050": https://www.healio.com/news/primary-care/20250306/projected-parkinsons-disease-cases-worldwide-set-to-hit-25-million-by-2050
3. JAMA Neurology (via PubMed) – "Risk of Parkinson Disease Among Service Members at Marine Corps Base Camp Lejeune": https://pubmed.ncbi.nlm.nih.gov/37184848/
4. ABC11/CNN – "Veterans exposed to chemical at Camp Lejeune faced a 70% higher Parkinson's risk": https://abc11.com/parkinsons-camp-lejeune-veterans-health-marines/13251726/
5. ABC News/Good Morning America – "Paraquat remains in the U.S. despite bans": https://www.goodmorningamerica.com/news/story/essential-herbicide-cost-paraquat-remains-us-despite-bans-102449938
6. Civil Eats – "Will Evidence on Paraquat's Health Risks Prompt an EPA Ban?": https://civileats.com/?p=61209
7. U.S. Federal Register (EPA) – "Extension of Postponement of Effectiveness for Certain Provisions of Trichloroethylene": https://public-inspection.federalregister.gov/2026-03155.pdf
8. New York State Senate, Bill S9094A (2025–26), background on paraquat and EPA review: https://legislation.nysenate.gov/pdf/bills/2025/S9094A
9. Michael J. Fox Foundation – "New Estimate Suggests 25 Million People with Parkinson's by 2050": https://michaeljfox.org/news/new-estimate-suggests-25-million-people-parkinsons-2050

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