More than 3,600 chemicals approved for food contact in packaging, kitchenware or food processing equipment have been found in humans, new peer-reviewed research has found, highlighting a little-regulated exposure risk to toxic substances.

The chemicals have been found in human blood, hair or breast milk. Among them are compounds known to be highly toxic, like PFAS, bisphenol, metals, phthalates and volatile organic compounds. Many are linked to cancer, hormone disruption and other serious health issues.

But many others are substances for which there are very limited public toxicological profiles, such as synthetic antioxidants used as preservatives and oligomers that stabilize ink on packaging. The study’s authors say the knowledge gaps highlight the need for further scrutiny of food contact chemicals.

“What is certainly of concern is that we have a strong link that shows some hazardous chemicals … migrate from packaging into food, so there is a contribution to exposure from packaging,” said Birgit Geueke, a study co-author with the Food Packaging Forum, a Zurich-based non-profit that advocates for stronger regulations.

The study identified about 14,000 chemicals approved for food contact, and checked databases and scientific literature for evidence of human accumulation on each. Humans are exposed to many of the chemicals in other scenarios, so the research does not mean to suggest that food packaging is solely responsible.

Among the worst offenders is plastic, a material that is largely unregulated and can contain thousands of chemicals. Silicone and coatings on metal cans can also contain toxic or understudied compounds, Geueke said. Many paper and cardboard products were until recently treated with PFAS and can contain a layer of plastic.

Several factors can cause chemicals to leach into food at higher rates, like higher temperatures, fat content and acidity. The ratio of packaging to product also matters – foods in smaller containers can be much more contaminated.

Many chemicals in the US are approved with limited scrutiny under the US Food and Drug Administration’s “generally regarded as safe” rule, which allows chemicals to be used for food contact with very little agency scrutiny. US law also does not require the FDA to consider new science after a chemical is approved for food contact.

That has been a problem with chemicals like PFAS or titanium dioxide that were on the market for decades before being removed or further studied. Though the European Union has in place stricter regulations for some chemicals, like PFAS, “there is still a lot of room for improvement”, Geueke said.

Consumers can protect themselves by buying foods in glass jars, which typically have very few chemicals. Some researchers who work in the field say they bring their own glass containers to restaurants in case they want to pack leftovers. Geueke said removing food from plastic containers bought at a store or from carryout containers and placing them in glass jars at home reduces the amount of time chemicals have to transfer from packaging.

“But you cannot completely avoid [the chemicals],” Geueke said, adding that the solution was stronger regulation.