Dozens of widely used chemicals could be toxic to gut bacteria, potentially affecting human health, according to a new study by UK scientists. Researchers tested more than 1,000 chemicals in the laboratory and identified 168 that appeared to prevent healthy gut bacteria from growing, raising concerns about their impact on the gut microbiome.
The gut microbiome consists of thousands of bacterial species and other microorganisms that live in the digestive tract. Scientists have linked it to numerous health outcomes, including cancer, heart disease, type 2 diabetes, insomnia, and complications during pregnancy such as preterm birth.
In the study, researchers tested 1,076 chemical contaminants—including pesticides, herbicides, industrial chemicals, and so-called “forever chemicals” like per- and polyfluoroalkyl substances (PFAS)—on 22 species of gut bacteria. Many of the harmful chemicals, including flame retardants and plasticisers used in everyday products, were not previously known to affect living organisms, the team said.
“We were surprised that some of these chemicals had such strong effects,” said Indra Roux, a researcher at the University of Cambridge and one of the study’s authors. “Many industrial chemicals that we are regularly in contact with weren’t thought to affect living organisms at all, but they do.”
The chemicals can enter the human body through food, water, and other environmental exposures. While the precise level of real-world exposure remains unclear, the researchers noted that environmental pollutants have been linked to changes in the gut microbiome that may contribute to obesity and insulin resistance.
Laboratory tests also revealed that some bacteria altered their functions to survive chemical exposure, which in some cases led to increased resistance to antibiotics. If similar effects occur in humans, this could make infections harder to treat and worsen the growing public health problem of antimicrobial resistance (AMR).
Traditionally, chemical safety assessments focus on the chemicals’ intended targets—such as how effectively a pesticide kills pests—without considering their potential impact on the human gut. “Safety assessments of new chemicals for human use must ensure they are also safe for our gut bacteria, which could be exposed to the chemicals through our food and water,” said Stephan Kamrad, another author from the University of Cambridge.
The study, published in Nature Microbiology, calls for more real-world data to determine whether laboratory findings translate to effects on human gut health. Meanwhile, researchers advise people to reduce exposure where possible, for example by washing fruits and vegetables thoroughly and avoiding the use of pesticides at home.
The findings add to growing evidence that everyday chemical exposures may have unintended consequences on human health, highlighting the need for more comprehensive safety testing that considers the gut microbiome.
