Can microplastics from baby bottles interfere with milk protein digestion in infants?

What's actually in it

Most baby bottles sold today are made from polypropylene (PP), a plastic considered safer than polycarbonate because it doesn't contain BPA. But polypropylene isn't inert. Studies have shown it can shed tiny plastic particles, especially when heated or sterilized repeatedly.

These particles are called microplastics (visible under a microscope) and nanoplastics (too small to see). When a bottle is filled with warm formula or breast milk, these particles float into the liquid that your baby drinks.

What the research says

A 2025 study in Environ Pollut tested what happens when polypropylene micro- and nanoplastics mix with cow's milk proteins during digestion. The researchers used a model that mimics an infant's stomach conditions: low acid, specific enzymes, and gentle movement.

They found that the plastic particles changed how milk proteins broke down. Some proteins that should have been fully digested weren't. Others broke apart in unusual ways. The plastic particles appeared to bind to the proteins and shield them from digestive enzymes.

This matters because incomplete protein digestion in infants can lead to larger protein fragments entering the gut. These fragments may trigger immune responses or allergic reactions. Babies' guts are more permeable than adults', so these fragments can pass through more easily.

Glass baby bottles eliminate this source of microplastics entirely. If you use plastic bottles, avoid aggressive sterilization with boiling water, which increases particle shedding. Let formula cool before pouring it into a plastic bottle.