A new large-scale laboratory analysis has identified 168 human-made chemicals from herbicides to insecticides capable of damaging beneficial gut bacteria, raising concerns over their long-term impact on public health.
Conducted by researchers at the University of Cambridge, the study screened 1,076 chemical contaminants against 22 common gut bacterial species, many of which support digestion, immunity and metabolic balance.
The findings reveal that several everyday industrial chemicals — including herbicides, insecticides, flame retardants and plasticisers — can suppress bacterial growth and, in some cases, trigger bacterial resistance to antibiotics such as ciprofloxacin. Pesticides are already known to cause acute symptoms like poisoning, respiratory distress, and skin/eye irritation, as well as long-term effects such as cancer, neurological disorders, and reproductive issues
Scientists warn that if similar effects occur inside the human gut, common infections could become increasingly difficult to treat.
Importantly, most of the chemicals flagged in the study were not previously considered harmful to gut microbes, even though they are likely to enter the body through food, water and environmental exposure.
The gut microbiome, a complex ecosystem of nearly 4,500 bacterial species, plays a key role in maintaining human health.
Disturbances in this system have been linked to digestive disorders, obesity, weakened immunity and even mental health concerns. Yet standard chemical safety frameworks do not factor in microbial impacts, as many products are designed to target insects or fungi, not humans.
To bridge this gap, the team has also developed a machine-learning model capable of predicting whether existing or emerging industrial chemicals may harm gut bacteria — a step researchers say could help guide safer chemical design in the years ahead.
Dr. Indra Roux from Cambridge’s MRC Toxicology Unit said the results challenge long-held assumptions. “We were surprised that many industrial chemicals thought to be harmless still had strong effects on gut bacteria,” she noted, as per the study published in Nature Microbiology.
Professor Kiran Patil in the University of Cambridge’s MRC Toxicology Unit and senior author of the study said: “The real power of this large-scale study is that we now have the data to predict the effects of new chemicals, with the aim of moving to a future where new chemicals are safe by design.”
Dr Stephan Kamrad at the University of Cambridge’s MRC Toxicology Unit, who was also involved in the study, said: “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.”
Very little information is available about the direct effects of environmental chemicals on our gut microbiome, and in turn our health. The researchers say it’s likely our gut bacteria are regularly being exposed to the chemicals they tested, but the exact concentrations reaching the gut are unknown. Future studies monitoring our whole-body exposure will be needed to assess the risk.
In the meantime, the researchers suggest the best way to try and avoid exposure to chemical pollutants is to wash our fruit and vegetables before we eat them, and not to use pesticides in the garden.
