Occupational Pesticide Exposure Raises ALS Risk by Up to 70%
Workplace herbicide exposure was linked to a 71% increased risk of ALS.
Could routine chemical exposure on the job be driving the steady rise in motor neuron disease cases?
In a systematic review led by researchers at Canada’s Occupational Health and Safety Research Institute and the University of Montreal, scientists evaluated 35 years of global occupational data.
Their findings revealed that workplace exposure to pesticides increases the risk of developing amyotrophic lateral sclerosis (ALS) by up to 70%, with exposed men facing double the risk of unexposed men.
Understanding how workplace pesticides influence ALS risk
ALS is a rare, fatal disease that targets the motor neurons controlling human muscle movement. While clinicians have watched ALS cases steadily rise over the years, global agricultural chemical use has also expanded significantly over the past three decades.
It has been shown that acute, short-term contact with pesticides can harm the central nervous system; however, what happens when someone works around these substances daily over an entire career has been far less studied.
“Exposure to pesticides was first proposed as a risk factor for ALS in 1980, and since then, numerous studies and various systematic reviews have explored their potential role in the onset of ALS,” said the authors of the latest study.
Earlier research has produced confusing, contradictory answers; previous reviews frequently lumped home gardening together with heavy industrial exposure or relied on job titles rather than tracking what workers handled.
The team conducted a fresh meta-analysis focused on workplace exposure. By isolating occupational settings, they aimed to measure how different chemical classes and exposure levels affect ALS risk and identify the design flaws that derailed previous studies.
What meta-analyses reveal about pesticides and ALS risk
The researchers looked through eight scientific databases for observational studies published between 1990 and 2025. Following PRISMA guidelines and WHO risk-of-bias frameworks, they focused on eight primary case-control studies covering 1,734 individual ALS cases. Using statistical regression models, the team pooled the data to evaluate how sex, chemical classes, exposure intensity, and research methods influenced the numbers.
Any workplace exposure to pesticides was associated with a 58%–60% increase in the risk of developing ALS compared with no exposure.
Exposed men were twice as likely to develop ALS as unexposed men, whereas exposed women showed no elevated risk.
Herbicides were linked to a 71% risk increase, while insecticides and fungicides were associated with an increase in ALS risk by 57% and 61%, respectively. High workplace exposure nearly tripled disease risk, compared with a near-doubling for low-level exposure.
Workers who failed to use personal protective equipment faced up to a 40% higher risk of disease compared to those who did.
The way scientists collected their data heavily dictated their final numbers. Studies relying on self-reported recall questionnaires calculated a 62% risk increase, whereas studies using expert hygiene evaluations found almost no additional risk. Older papers published before 2016 also reported much higher risk estimates than recent ones, accounting for two-thirds of the variation between studies.
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Reducing workplace chemical exposure to prevent ALS
These findings offer evidence that occupational chemical exposure represents a genuine, modifiable risk factor in the relationship between pesticides and ALS. Improving workplace safety protocols, enforcing personal protective gear, and reducing routine exposure on the job could provide meaningful protection for vulnerable workers.
At the same time, the authors emphasized that current scientific evidence still suffers from limitations. Only a small pool of primary studies met the criteria for meta-analysis, making it impossible to evaluate specific active ingredients. Most relied on questionnaires prone to memory errors, and many failed to account for unmeasured factors such as past head trauma or drinking private well water.
“To strengthen the evidence on risk factors for ALS, primary studies particularly need methodological improvements on exposure assessment, on the selection of reference groups, and on adjustment for potential confounders, including analysis for interactions between risk factors,” said the authors.
Despite these caveats, the fundamental takeaway points to the need for preventive action.
“The findings of this review add to the evidence that occupational exposure to pesticides may increase the risk of ALS and should encourage the implementation of interventions aimed at reducing exposure during occupational pesticide use,” concluded the team.
Reference: Labrèche F, Prud’homme P, Gagnon M, Dupré N, Gravel S. Occupational exposure to pesticides increases the risk of amyotrophic lateral sclerosis: a systematic review and meta- analysis. Occupat Environ Med. 2026. doi: 10.1136/oemed-2025-110662
This article is a rework of a press release issued by the BMJ Group. Material has been edited for length and content.
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