A large laboratory study by the University of Cambridge in the UK has found that dozens of chemicals widely used in everyday life, often found in pesticides and industrial products may be damaging beneficial gut bacteria, raising concerns about unseen effects on human health.

The scientific-led study analysed 1,076 human-made chemicals and found 168 of them were harmful to bacteria that normally live in a healthy human gut. The findings were published this week in the journal Nature Microbiology.

Researchers tested the chemicals on 22 species of gut bacteria under laboratory conditions. Many of the substances that slowed or stopped bacterial growth are commonly encountered through food, drinking water and the environment. Until now, most were not believed to affect living organisms at all.

The study also found links between chemical exposure and antibiotic resistance. When gut bacteria were stressed by certain pollutants, some altered their behaviour to survive. In some cases, these changes also made the bacteria resistant to antibiotics such as ciprofloxacin, a widely used treatment for bacterial infections.

The chemicals identified as most harmful included pesticides such as herbicides and insecticides applied to crops, as well as industrial compounds used in flame retardants and plastics. According to the study, disruption of the gut microbiome – which contains an estimated 4,500 different types of bacteria – has previously been associated with digestive problems, obesity, weakened immune function and effects on mental health.

Researchers said current chemical safety testing typically does not consider impacts on the gut microbiome, because products are designed to target specific organisms or processes, such as insects or fungi.

University of Cambridge MRC Toxicology Unit Researcher, and the study’s first author Dr Indra Roux said: “We’ve found that many chemicals designed to act only on one type of target, say insects or fungi, also affect gut bacteria. We were surprised that some of these chemicals had such strong effects.

“For example, many industrial chemicals like flame retardants and plasticisers – that we are regularly in contact with – weren’t thought to affect living organisms at all, but they do.”

Using data from the experiments, the research team developed a machine-learning model designed to predict whether industrial chemicals – already in use or still in development – are likely to harm gut bacteria.

Senior author on the study, Professor Kiran Patil, 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, another researcher who was involved, 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.”

Researchers noted that significant gaps remain in understanding how environmental chemicals affect the gut microbiome in real-world conditions. While gut bacteria are likely exposed to many of the tested substances, the amounts that reach the digestive system are not yet clear.

“Now we’ve started discovering these interactions in a laboratory setting it’s important to start collecting more real-world chemical exposure data, to see if there are similar effects in our bodies,” Patil said.

Until more evidence is available, the researchers recommend simple measures to reduce exposure, including washing fruits and vegetables before consumption and avoiding the use of pesticides in home gardens.