Can plastic water bottles and milk cartons shed microplastics into your drinks?

What's actually in it

Plastic water bottles are typically made from PET (polyethylene terephthalate), while milk often comes in HDPE (high-density polyethylene) jugs or multilayer cartons with plastic linings. Both types of packaging can shed tiny plastic fragments into the liquid inside. These fragments are microplastics, particles smaller than 5 millimeters that you can't see or taste.

The shedding happens slowly during normal storage and speeds up with heat, sunlight, or physical stress like squeezing the bottle. The longer a drink sits in its plastic container, the more particles accumulate.

What the research says

A 2025 study in Environ Monit Assess tested drinking water bottles and milk packaging to identify and count the microplastics inside. The researchers used microscopy and spectroscopy to determine what types of plastic the particles were made from.

They found microplastics in every sample tested. The particles matched the packaging material itself: PET fragments in water bottles, polyethylene fragments in milk containers. This confirms the packaging is the direct source, not some outside contamination.

Water bottles that had been stored longer or exposed to warmer conditions had higher microplastic counts. Milk packaging showed similar patterns. The particle sizes ranged from large enough to see under a microscope down to near-nanoscale, which is small enough to potentially cross the gut barrier.

Glass bottles, stainless steel water bottles, and cartons with minimal plastic lining are lower-risk alternatives. If you buy plastic bottles, store them in a cool, dark place and don't reuse single-use bottles.