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Most of the focus on insecticides’ health hazards has been on neurological systems such as electrical signaling at synapses in neural networks, especially in the brain.
However, a study in Toxicology, by authors at the Skeletal Muscle Lab, Institute of Integrated and Honors Studies, Kurukshetra University, India, finds that a widely used synthetic pyrethroid insecticide used for indoor and outdoor household pests damages muscles.
While synthetic pyrethroids are known to attack calcium and sodium channels, affecting neuronal electrical signaling, this study opens up yet another realm of biochemical pathways in the body that are not evaluated in the regulatory review — allowing widespread exposure to a family of pesticides that are established to have common toxicological properties.
The subject of this in vitro study is transfluthrin, a synthetic pyrethroid (originally registered in 2018 with new uses permitted in 2023) used to control flying and crawling household pests (mosquitoes, flies, moths and cockroaches) as a contact poison and in vaporizers, including aerosol sprays and mosquito coils, patio lanterns, etc.
An earlier epidemiologic study using National Health and Nutrition Examination Survey data found pyrethroid exposure adversely affects handgrip strength and skeletal muscle mass.
“This study demonstrates, for the first time, that TF [transfluthrin] directly impairs skeletal muscle cell metabolism by inducing oxidative stress, mitochondrial dysfunction, atrophy, and altered glucose utilization,” the authors wrote, “highlighting under-recognized health risks associated with excessive routine household insecticide exposure.”
Importantly, this study reveals a completely different mechanism of action in addition to the known neurotoxic effects upon which pyrethroid regulation is currently based.
Pyrethroids are touted as “safer” than previous classes of insecticides — they were introduced in the 1960s, just as DDT’s (dichlorodiphenyltrichloroethane) depredations were being acknowledged, because they are synthetic compounds similar to chemicals in asters and chrysanthemums.
They are widely used in household pesticides against moths, mosquitoes, bedbugs, dog and cat fleas and other arthropods. However, they are far from benign. They are highly toxic to cats, and resistance has developed among bedbugs, moths and mosquitoes.
(NOTE: The Farm Bill passed by the U.S. House of Representatives and the U.S. Senate Agriculture Committee on its way to the Senate floor includes a provision — Section 10201. Biostimulants — which exempts from regulatory review “biostimulants that … (ii) are of biological origin or include chemical compounds that are synthetically derived but structurally similar and functionally identical to substances of biological origin [emphasis added],” thus ignoring the biochemical pathways addressed in this study and the scientific literature on synthetically derived but structurally similar compounds, like synthetic pyrethroids. For readers who have not commented on the Senate Farm Bill, see action.)
Muscles regulate glucose homeostasis. They take up 80% of ingested glucose and use most of it during exercise.
Because of the importance of glucose metabolism to overall health, its disruption at the cellular level in muscle tissue not only leads to physical weakness and wasting, but it is directly implicated in metabolic diseases such as diabetes and cardiovascular disorders.
See Beyond Pesticides’ Daily News Blog of April 3, analyzing a study linking pyrethroid exposure to cardiac dysfunction.
The current study, currently in preprint, examines in fine detail what happens to muscle components called myotubes when exposed to transfluthrin. Exposure to transfluthrin, a large molecule with both chlorine and fluorine atoms, is primarily through inhalation.
There has been a great deal of research into the efficacy of transfluthrin-drenched fabrics for killing or discouraging mosquitoes in tropical and desert environments, including in military situations.
Some of these products are designed as human clothing. In 2023, the U.S. Environmental Protection Agency (EPA) registered a new mosquito repellent consisting of a wax pod in a lantern-heated tray for use in outdoor and semi-enclosed areas such as patios, tents and recreational vehicles.
Previously, transfluthrin had been registered only for an indoor product to kill moths. Its effectiveness against mosquitoes has been heavily stressed in the research literature, especially in military applications, although one study found that transfluthrin passive diffusers had no protective effect in two-person military tents.
A 2023 study by Indian researchers found that exposure to transfluthrin was strongly associated with asthma susceptibility in children.
A Chinese study from 2025 using protein-protein interaction analysis likewise found pyrethroid exposure, including to transfluthrin, is highly associated with respiratory diseases including asthma, chronic obstructive pulmonary disease and pulmonary fibrosis.
Previous research has shown that transfluthrin affects acetylcholinesterase activity, produces reactive oxygen species and oxidative stress, and eventually affects fertility, number of offspring, mating frequency and other reproductive problems in laboratory animals.
The current study includes several layers of investigation into transfluthrin’s effects on the molecular biology of myotubes. These are structures comprising long cells with multiple nuclei involved in the stretching and contracting actions of muscles.
The authors note that muscle tissue can comprise up to 50% of body tissue and, unlike the brain, has no defense against xenobiotics circulating in the blood, particularly since it has many blood vessels.
The researchers exposed myotubes to varying doses of transfluthrin. They found that the myotubes change shape and show a “dose-dependent increase in glucose consumption and uptake.”
The degradation of the myotube structures shows that the increased glucose utilization does not indicate improved muscle function.
They hypothesize that transfluthrin might enhance glucose storage as glycogen, or it might increase glucose breakdown. They find it does the latter, leading to increased lactate, which is known to damage mitochondria.
Further investigation of the mitochondria reveals that transfluthrin depolarizes the mitochondrial membrane, an important electrical component for mitochondrial energy production. The myotubes’ physical shape also changed. They shrink in both length and diameter.
Following up on earlier work establishing that reactive oxygen species and oxidative stress damage mitochondria, the researchers examine what oxidative stress does to myotubes.
Many xenobiotics introduce too many oxygen molecules into cells, causing oxidative stress when the oxygen attacks cellular components, particularly mitochondria.
The study authors find that transfluthrin exposure elevated the level of reactive oxygen species, and that glutathione, a key defense against oxidative stress, is reduced, indicating muscular atrophy.
Transfluthrin-exposed myotubes’ ability to maintain homeostasis by cleaning out damaged and aged proteins is also disrupted. In fact, those myotubes are too clean — have too few proteins — another indication of muscular atrophy.
The authors hypothesize that transfluthrin exerts its extremely harmful effects by increasing the demand for glucose because the cell does not store it as glycogen but instead breaks down glucose and disposes of it.
Glucose is necessary for the production of the energy-producing molecule adenosine triphosphate (ATP), which every form of life uses, and any interference with this process will produce disease.
The disease gradient goes both ways; also, metabolic diseases such as diabetes and obesity promote muscle degeneration, and disruption of muscles at the molecular level raises the risk of these chronic diseases.
Transfluthrin has received relatively little attention for its toxic effects compared to other pyrethroids, but exposure to this class of pesticides is ubiquitous, and if the diffusion-based products being developed commercially and militarily proliferate, more people will be exposed specifically to transfluthrin.
The EPA is not worried. According to its most recent human health assessment for transfluthrin, “After reviewing the extensive body of peer-reviewed literature on pyrethroids, the agency has no residual uncertainties regarding age-related sensitivity for women of child bearing age, as well as for all adult populations and children >6 years of age.”
The authors of the current study caution that their work is in vitro, meaning it needs to be expanded upon with further in vivo (in laboratory organisms) studies before firm conclusions can be drawn.
The rapidly expanding body of evidence from in vitro and in silico (computer) studies indicates that pesticides and xenobiotics have many common mechanisms of action at the cellular and molecular levels, leading to stresses implicated in a wide range of diseases.
This in vitro study introduces another route by which pesticides exert extreme harm, which must be further investigated.
The study adds to the body of science that illustrates the serious inadequacy of the regulatory review and risk assessment process that is used to allow widespread use of toxic pesticides.
In this spirit, plan now to join us for Beyond Pesticides’ 2026 National Forum, Advancing Science on Pesticides, Taking Action in Harmony with Nature, and Sustaining Life. The forum is organized to empower effective action and chart a path for a livable and sustainable future.
With groundbreaking scientists speaking on the pesticide threat to human health and ecosystems, we empower ourselves and our communities with the compelling reasons to act urgently.
The forum brings us into conversation with the science—made simple—that we need to use as a tool for advancing necessary change. The failure of decision-makers and policymakers to respond to the seriousness of the current pesticide-induced threats continues at our peril.
The science, if widely discussed and understood, provides the impetus to adopt sustainable practices that are available to us. You are part of the solution! See details and register here. It’s free.
You can directly reduce your risk by not using pyrethroid products indoors or outdoors. See Beyond Pesticides’ resource on synthetic pyrethroids in our Gateway on Pesticide Hazards and Safe Pest Management for more information on these chemicals’ numerous other health effects.
Originally published by Beyond Pesticides.
