It has long been known that the pesticide chlorpyrifos has harmful health effects on humans, especially developing fetuses and children. Unfortunately, it is still in use.
A recent review of nearly 300 studies looking at chlorpyrifos found that the pesticide has harmful effects throughout the body, also causes DNA damage, harms children's brains and nervous systems, causes cancer.and that harmful effects are found at levels that are considered safe by the EPA. Unfortunately, more health harms are found each year.
While the pesticide is no longer allowed to be used for household use in the US (remember cans of Raid cockroach killer?), it is still allowed to be used on farms, in greenhouses, golf courses, and more. Keep in mind that industry-funded studies of chlorpyrifos have been used to shape federal policy and exposure limits for decades.
In other words, federal standards do not protect public health. Why is that not surprising?
Excerpts from the investigative journalism site U.S. Right To Know: Nearly 300 studies link the common pesticide chlorpyrifos to multi-organ damage, DNA disruption, and chronic disease
Key findings:
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- A review of nearly 300 studies summarizes evidence that chlorpyrifos may harm multiple systems throughout the body, including the brain, hormones, liver, gut microbiome, muscles, reproductive organs, and bones.
- The review describes DNA damage, chromosome instability, and epigenetic changes that may alter how genes function long after exposure.
- Some harmful effects appear at exposure levels below those considered safe under current pesticide exposure testing standards.
For decades, regulators viewed chlorpyrifos — a pesticide widely used in the U.S. and around the world — primarily as a neurotoxin that disrupts signaling in the brain and nervous system. But as the EPA reconsiders whether to continue to allow its use on foods like apples and soybeans, a new review indicates other insidious harms.
Published in April [2026] in the International Journal of Molecular Sciences, the review synthesizes findings from nearly 300 studies worldwide published up to this year. These include laboratory experiments, animal studies, epidemiological research, regulatory documents, and risk assessments.
Growing evidence suggests chlorpyrifos may damage the brain, hormones, liver, gut microbiome, muscles, reproductive organs, and bones. Studies also link the pesticide to DNA damage and lasting changes in gene activity that may increase the risk of chronic disease.
Together, the findings portray chlorpyrifos as what the reviewers call a “multi-system toxicant” that poses a more significant threat to public health than previously understood. It suggests the pesticide acts on the body in ways far beyond disrupted nerve signaling or obvious poisoning. Pregnancy and early childhood are especially sensitive periods for chemical exposure.
“What has genuinely evolved over time is our understanding that chlorpyrifos causes harm in ways that go beyond its effects on the nervous system including damage to DNA, changes in how genes are switched on or off, interference with hormones, and disruption of the healthy bacteria that live in the gut,” said Dr. Dana Boyd Barr, a professor at Emory University’s Rollins School of Public Health and past president of the International Society of Exposure Science.
The authors warn that current regulatory systems may not fully capture the complexity of chlorpyrifos’ dangers to the body. Many occur at levels too low to be detected by current safety testing, which looks for the disruption of an enzyme involved in nerve cell communication.
The review links chlorpyrifos exposure to:
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- Biological changes associated with inflammation, chronic disease, and cancer
- Brain and nervous system damage, including lower IQ and developmental harms in children, neurodegenerative disease, and disrupted cell growth, survival, and communication
- DNA damage and altered gene regulation that hinders normal cell repair and changes how genes are switched on and off during development (epigenetics)
- Hormone disruption involving thyroid, estrogen, and testosterone pathways
- Liver injury, gut bacteria disruption, and metabolic dysfunction linked to obesity and type 2 diabetes
- Reproductive, muscular, and skeletal harm, including reduced sperm quality and bone loss
Industry pushback despite reported harms
The review comes as the EPA reassesses whether the pesticide’s remaining uses meet the statutory standard of “no unreasonable adverse effects.” The action follows years of official stalling, prior bans, policy reversals, and legal challenges.
Meanwhile, agrichemical companies are lobbying federal and state lawmakers to shield pesticide manufacturers, including Bayer and its subsidiary Monsanto, from some lawsuits involving Roundup weedkiller. The suits allege their products cause non-Hodgkin lymphoma (NHL), among other cancers.
In February 2020, Corteva Agriscience—then the world’s largest producer of chlorpyrifos — announced it would stop production, citing declining demand. But existing stocks continued to be used. The chemical remains approved for several major crops in the U.S., including apples, strawberries, soybeans, citrus, wheat and peaches.
Health concerns trigger restrictions and bans
Chlorpyrifos — the active ingredient in Dursban® and Lorsban® — belongs to a class of chemicals known as organophosphates. Introduced in the U.S. in 1965, chlorpyrifos became one of the world’s most heavily used insecticides by the 1990s.
Farmers use chlorpyrifos to control ticks on cattle and pests on crops. It is used on golf courses, in greenhouses, on wood products such as telephone poles, and in residential areas
U.S. regulators banned chlorpyrifos for household use in 2001. The ban came after mounting evidence, including a prominent study by Columbia University, linked exposure to developmental brain harms in children.
Evidence that chlorpyrifos damages children’s brains later prompted bans or restrictions in more than 40 countries, including the European Union. The European Food Safety Authority concluded there was no safe exposure level, but it is still widely used elsewhere in the world. Several U.S. states, including California, New York, Hawaii, Oregon and Maryland, currently maintain restrictions or bans.
Yet chlorpyrifos persists in food (including fruits, cereals, and vegetables), the environment, and human tissue. The compound dissolves easily in fats and crosses cell membranes, allowing it to accumulate in tissues over time.
It can also travel long distances — in some cases more than 600 miles — from where it was applied. Researchers have detected residues in food, drinking water, soil, rain, snow, and wildlife. Samples range from the Mississippi River to remote Antarctica.
The American Academy of Pediatrics warns that chlorpyrifos exposure poses risks to fetuses, infants, children, and pregnant women. Chlorpyrifos crosses the placenta and injures the developing nervous system before birth.
“Chlorpyrifos poses a significant neurotoxic risk to humans, with developing fetuses and children being particularly vulnerable,” they wrote. “Neurotoxic effects of the pesticide have been observed even at low doses.”
Prenatal exposure linked to lasting brain damage and lower IQ
Human studies link prenatal chlorpyrifos exposure to:
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- Attention deficits
- Delayed motor development
- Lower birth weight
- Reduced IQ
- Structural brain abnormalities
For instance, an August 2025 study of New York City children found that prenatal exposure to chlorpyrifos was linked to widespread brain abnormalities and weaker motor skills years later. The researchers concluded prenatal exposure may cause lasting brain disruptions. The effects appeared to worsen with higher exposure.
Perhaps most striking, chlorpyrifos appears in these studies to suppress brain-derived neurotrophic factor (BDNF). BPA, flame retardants, and other toxic chemicals also disrupt BDNF, which Dr. Bruce Lanphear describes as “fertilizer for the brain.”
“What emerges is a troubling picture: the developing brain is being shaped by a toxic soup of chemicals acting on the same parts of the brain,” said Lanphear, a preventive medicine physician and professor at Vancouver’s Simon Fraser University who studies how toxic chemicals impact human health. “Yet when the EPA evaluates chlorpyrifos, it largely considers the pesticide on its own—not alongside other chemicals that disrupt the same brain pathways.”
The ways chlorpyrifos affects the body may contribute to the growth and rate of liver, breast, and ovarian tumors, studies indicate. One large 2015 study of more than 30,000 women—spouses of pesticide applicators—linked chlorpyrifos exposure to elevated breast cancer risk. While human evidence remains limited and inconsistent, the reviewers say, the combination of effects warrants closer investigation.
Additionally, 3D laboratory models suggest that chlorpyrifos may cause breast cancer cells to invade nearby tissues more actively. Epidemiological studies also report associations with hormone-related cancers, particularly more aggressive forms of hormone receptor-negative breast cancer.
The review cites evidence linking chlorpyrifos exposure to movement problems, memory impairment, anxiety-like behaviors, and damage to brain regions involved in emotion and cognition. One recent study reports that chlorpyrifos exposure may be associated with more than double the risk of Parkinson’s disease.
Researchers say chlorpyrifos-oxon (CPO) — produced when the body breaks down chlorpyrifos — may be especially dangerous. According to federal researchers, chlorpyrifos-oxon is about 1,000 times more toxic than chlorpyrifos itself.
The review finds substantial evidence that chlorpyrifos may interfere with multiple hormone systems (endocrine disruption) throughout the body. These include thyroid, estrogen, and testosterone pathways.
Research links exposure to abnormal reproductive cycles and tissue development, lower sperm counts, and reduced sperm quality. Some studies suggest it causes reduced prostate weight and disrupted hormone signaling in placental cells. Chlorpyrifos may also contribute to obesity, insulin resistance, and blood sugar problems, the review shows.
The review also tracks harms involving the gut microbiome — the ecosystem of microbes that supports digestion, metabolism, and immune function. Experimental studies indicate reductions in beneficial bacteria alongside increases in potentially harmful microbes after chlorpyrifos exposure.
These changes may be tied to leaky gut syndrome, when bacterial toxins enter the bloodstream and trigger inflammation throughout the body. This type of gut-liver axis disruption may contribute to systemic inflammation and metabolic disease, the reviewers say.
The liver itself emerges as a major target of chlorpyrifos, experimental studies show. Researchers describe potential ties between chlorpyrifos and:
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- Chronic liver inflammation
- Disrupted cholesterol, with higher levels of LDL (“bad”) cholesterol and lower HDL (“good”) cholesterol
- Liver cell injury, including a form of cell death linked to iron buildup in liver cells (ferroptosis)
The review also links chlorpyrifos to musculoskeletal damage, including weaker bone formation, reduced bone density, and increased bone breakdown. Some bone changes occurred alongside neurological problems, suggesting broader developmental damage.
The review highlights growing evidence that chlorpyrifos may damage DNA. Researchers describe chromosome damage and broken DNA strands.
The ways chlorpyrifos affects the body may contribute to liver, breast, and ovarian tumors, studies indicate. These include changes in DNA damage and repair, cell growth control, and gene expression.
One large 2015 study of more than 30,000 women—spouses of pesticide applicators—linked chlorpyrifos exposure to elevated breast cancer risk. While human evidence remains limited and inconsistent, the reviewers say, the combination of effects warrants closer investigation.
Underlying the review is a larger challenge to how regulators evaluate the safety of chlorpyrifos and other pesticides. Current approaches, the authors say, do not adequately account for their effects, especially during fetal development and early childhood.
“The regulatory system was designed to prevent obvious poisoning, but many pesticide-related diseases do not appear immediately. Exposures too low to cause symptoms today may impair fetal brain development or contribute to Parkinson’s disease decades later,” Lanphear added. “The science has moved ahead of the regulatory framework. That is the gap this review highlights.”
They also revisit longstanding criticism of industry-funded chlorpyrifos studies that have been used to shape federal exposure limits for decades. They cite the so-called “Coulston study,” a 1972 safety evaluation funded by Dow Chemical.