Most of the focus on insecticides' health hazards has been on neurological systems. But a new study in Toxicology, by authors at the Skeletal Muscle Lab at the Institute of Integrated and Honors Studies in Kurukshetra University, India, finds that a widely used synthetic pyrethroid insecticide used for indoor and outdoor household pests damages muscles.

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.)