Heating Baby Bottles Releases Microplastics Into the Milk

Heating a baby's plastic bottle releases millions of micro- and nanoplastics into the milk. A 2025 study found that sterilizing and warming polypropylene bottles significantly increases the concentration of microplastics in the milk or formula inside.

What the Research Found

Published in a peer-reviewed study (2025), researchers looked at how micro- and nanoplastics (MNP) from polypropylene baby bottles affect the digestion of cow's milk protein. They found that heating promotes the generation and migration of MNP into the liquid.

The particles don't just sit there. They bind to the proteins in the milk and alter how those proteins digest in the infant's gut. This is a mechanism by which plastic particles could affect infant nutrition and gut health, beyond just being a foreign material that the body has to deal with.

Polypropylene Is the Standard

Most plastic baby bottles are made from polypropylene (PP), labeled with the recycling symbol "5." PP is marketed as heat-stable. But "heat-stable" doesn't mean "no microplastics released." Under the heat of sterilization (100°C in boiling water), PP sheds particles. Every sterilization cycle makes the bottle shed more.

Glass baby bottles release zero microplastics when heated. Stainless steel bottles with no plastic lining do the same. These materials have been used safely for generations without needing to shed particles. Browse non-toxic baby products for glass and stainless baby bottles.

Also see glass food storage for safer alternatives.

Source: Polypropylene micro- and nanoplastics affect the digestion of cow's milk protein (2025).