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Microplastics in Baby Bottles: How to Sterilize Safely
A landmark study found that heating formula in polypropylene bottles exposes babies to millions of microplastics daily. Here is what you need to know.
R
By Renee, R3 Founder
Environmental Toxins Analyst
Updated June 2026
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The quick answer
A 2020 study from Trinity College revealed that standard polypropylene (PP) plastic baby bottles shed millions of microplastic particles per liter when exposed to hot water during standard sterilization or formula preparation. To prevent your baby from ingesting these plastics, you must either switch to glass bottles or prepare/cool the formula in a separate glass container before transferring it to the plastic bottle.
In this guide:Switch to Glass BottlesUse Medical Grade Silicone
Editor's note. This deep dive isolates the mechanical forces (heat and vigorous shaking) that cause polypropylene degradation.
01
The Trinity College Study Explained
The 2020 Trinity College study, published in Nature Food, simulated standard WHO guidelines for sterilizing baby bottles and preparing formula, and the results were shocking. Using hot water (158°F / 70°C) inside standard polypropylene bottles caused the plastic to shed millions of microplastic particles per liter.
The Trinity College researchers calculated that the average bottle-fed infant is ingesting over 1.5 million microplastic particles every single day. The hotter the water, the more plastics were shed. Shaking the bottle to mix the formula acted as a mechanical abrasive, drastically increasing the particle count.
The 2020 Trinity College study found that hot water at 158°F (70°C) in standard polypropylene baby bottles sheds enough microplastics that the average bottle-fed infant ingests over 1.5 million particles per day.
In short
- Polypropylene (PP) bottles shed heavily under heat.
- Average infant ingests 1.5M particles daily.
- Shaking hot bottles acts as an abrasive, worsening shedding.
02
How to Feed Safely
Glass bottles are the only foolproof way to eliminate the microplastic shedding that the 2020 Trinity College study documented in polypropylene bottles exposed to 158°F (70°C) water.
However, if daycare requires plastic, or your baby stubbornly prefers a specific plastic bottle, you can dramatically reduce microplastic exposure by changing your preparation method:
1. Boil water in a stainless steel kettle. 2. Pour the water into a glass jar or glass measuring cup. 3. Mix the formula powder into the glass container and shake/stir vigorously. 4. Let the formula completely cool to room temperature. 5. Only once it is cool, transfer it to the plastic baby bottle to feed.
By ensuring the plastic is never exposed to heat or aggressive shaking, you limit the polymer degradation.
Preparing formula in a glass container and transferring it to the plastic bottle only after it cools keeps polypropylene away from the heat and shaking that drive microplastic shedding.
In short
- Glass is the only 100% solution.
- Never shake hot water in a plastic bottle.
- Prepare formula in glass, then transfer when cool.
The bottom line
Never heat plastic, and never put hot liquid into plastic. Standard sterilization routines involving boiling water in plastic bottles are inadvertently creating massive microplastic exposure events.
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Cited research
Frequently asked questions
Common questions about toxicology: plastics, answered by our research team.
QWhat are the health impacts of ingesting microplastics?
The long-term health effects of microplastic ingestion in human infants are still under intense scientific investigation. However, microplastics are known to act as vectors, carrying heavy metals and endocrine-disrupting chemicals with them as they pass into the bloodstream and organs.
QAre silicone bottles safe from microplastics?
Silicone bottles do not shed microplastics, because silicone is a synthetic rubber made primarily from silica (sand), not a petroleum-based plastic. However, at extreme temperatures, some lower-grade silicones can leach siloxanes, so look for medical-grade or platinum-cured silicone.