Can old plastic water bottles cause fatty liver disease?

What's actually in it

Plastic water bottles are made from PET (polyethylene terephthalate). When these bottles sit in warm places like car trunks, garages, or sunny windowsills, the plastic ages faster. Aged PET breaks apart into microplastics that shed into your water.

These aged microplastics aren't the same as fresh ones. Heat and UV light change their surface chemistry, making them more reactive and potentially more harmful once they get inside your body.

What the research says

A 2026 study in Environ Sci Technol tested what happens when you ingest microplastics from heat-aged PET bottles. The researchers found that aged PET microplastics caused fatty liver disease (hepatic steatosis) in animals.

The damage worked through the gut-liver axis. Aged microplastics first disrupted the gut lining, letting bacterial toxins leak into the bloodstream. Those toxins traveled straight to the liver, where they triggered fat accumulation and inflammation.

Fresh microplastics from new bottles caused less damage than aged ones. The thermal aging process created new surface chemicals on the plastic that made them more toxic to gut and liver cells.

The study suggests that reusing old plastic bottles, or drinking from bottles that have been stored in hot conditions, may be riskier than using fresh ones. But the safest option is to skip single-use plastic bottles entirely.