Can polypropylene microplastics in infant formula or bottles worsen milk allergies in babies?

What's actually in it

Most plastic baby bottles and formula packaging are made from polypropylene (PP), one of the most common plastics. Studies have documented that preparing formula in polypropylene bottles, especially with hot water, releases millions to billions of microplastic particles per liter. Infants on formula drink these particles daily.

The immune system in infancy is learning to distinguish between harmless food proteins and actual threats. Cow's milk allergy happens when the immune system misidentifies milk proteins as dangerous and mounts an allergic (Th2) response. Anything that skews the immune system toward Th2 during this learning period makes food allergy more likely.

What the research says

A 2026 study in J Agric Food Chem used a murine model of cow's milk allergy and added oral polypropylene microplastic exposure on top of milk antigen exposure. Animals with microplastic exposure had significantly worse allergic responses to milk proteins than those without. The mechanism: PP microplastics pushed dendritic cells (immune teacher cells) and T cells toward a Th2 allergic profile.

The Th2 skewing effect means microplastics are specifically promoting the type of immune response that causes food allergies. For infants already at risk for allergy (with a family history, or with eczema), this immune tilting from microplastics adds to the risk.

For formula-fed infants, using glass bottles eliminates polypropylene microplastic release entirely. If plastic bottles are used, preparing formula with water at room temperature rather than hot water reduces (but doesn't eliminate) microplastic release. Stainless steel baby bottles are another alternative that avoids plastic entirely.