Plastic breast milk storage bags release microplastics into stored milk, according to recent research, and heat exposure can double the contamination levels. A 2025 study published in Food Control tested plastic baby bottles and breast milk storage bags and found that both release microplastics into breast milk. The research also revealed that heating milk increased microplastic exposure two-fold, raising concerns about how families store and prepare pumped milk for their infants.

What Are Microplastics and Why Should Parents Care?

Microplastics are tiny particles of plastic that break down from larger plastic items over time. They've become ubiquitous in modern life, infiltrating everything from cosmetics and fabrics to food packaging and household dust. Once released, these particles can enter the human body through various routes. Research has documented microplastics in the lungs, heart, liver, spleen, brain, kidneys, and small intestine.

A 2024 study in the Journal of Clinical Medicine found microplastics in approximately 39% of the 59 breast milk samples tested. Beyond the particles themselves, plastic products also contain chemical additives like phthalates and Bisphenol A (BPA), which are used to make plastic flexible and durable. According to pediatrician and founder of Ahimsa, a plastic-free feeding products company, these chemicals pose a distinct concern from the microplastics themselves.

"Neither of them is good because these are synthetic things that should not be circulating in the human body," explained Dr. Manasa Mantravadi, board-certified pediatrician and founder of Ahimsa.

Dr. Manasa Mantravadi, Board-Certified Pediatrician and Founder of Ahimsa

The American Academy of Pediatrics (AAP) acknowledges possible harmful effects from plastic chemicals, including endocrine disruption (interference with hormone systems), increased obesity risk, and negative effects on brain development. However, the AAP also notes that breastfeeding remains beneficial despite these concerns, as low concentrations of BPA have been found in breast milk.

How Does Heat and Storage Affect Microplastic Release?

The 2025 Food Control study revealed that storage conditions significantly impact microplastic exposure. Heat was the most dramatic factor, increasing microplastic levels two-fold compared to room-temperature storage. The research also found that during months when babies had higher nutritional requirements, microplastic levels in stored milk increased, suggesting infants face variable exposure depending on feeding patterns and storage methods.

Dr. Carol Duh-Leong, a pediatrician and assistant professor at NYU Grossman School of Medicine who researches breast milk storage practices, emphasized the importance of understanding real-world conditions. She noted that scientists are actively studying how plastic containers shed microplastics, particularly when exposed to heat, repeated use, and mechanical stress. However, she stressed that more research specifically focused on infants is urgently needed.

"Now that scientists are actively studying how plastic containers may shed microplastics, particularly with heat, repeated use, and mechanical stress, it is particularly important to anchor these experiments in real-world conditions," stated Dr. Carol Duh-Leong, pediatrician and assistant professor at NYU Grossman School of Medicine.

Dr. Carol Duh-Leong, Pediatrician and Assistant Professor at NYU Grossman School of Medicine

Ways to Reduce Microplastic Exposure When Storing Breast Milk

While the presence of microplastics in breast milk storage is concerning, experts emphasize that feeding your baby remains the priority. Dr. Mantravadi acknowledges the significant effort required to care for an infant and recommends practical steps to minimize exposure without adding stress to an already demanding routine.

• Avoid heating milk in plastic containers: Never warm breast milk directly in a plastic bag or bottle. Research shows that heat significantly increases microplastic release. Instead, thaw milk in the refrigerator and transfer it to a glass or stainless steel container for warming.
• Minimize agitation of stored milk: Avoid vigorously shaking breast milk storage bags. Increased friction between the milk and plastic surfaces can increase microplastic exposure. Gently swirling the bag is a safer alternative.
• Hand wash plastic storage containers with warm water: High-heat dishwasher cycles can degrade plastic and increase microplastic release. Use warm water and soap to clean pump parts and plastic milk storage containers instead.
• Store milk in glass or stainless steel when possible: If accessible and feasible for your family, storing pumped milk in glass or stainless steel containers eliminates the microplastic exposure from plastic storage entirely.

Dr. Mantravadi reminds parents that perfection is not the goal. "The most important part is that you are doing the best for your baby in the moment, with the knowledge that you have," she said. Small changes can accumulate over time, and until policy and industry standards catch up with the science, families should focus on manageable adjustments.

Is Breastfeeding Still Worth It Despite Microplastic Exposure?

Despite the presence of microplastics in breast milk, experts unanimously affirm that breastfeeding remains beneficial. Amy Spangler, a registered nurse and International Board Certified Lactation Consultant, emphasized that any amount of breastfeeding for any duration still provides significant health benefits to infants.

"Sadly, microplastics are already present in the milk of most mothers, and while the use of plastic storage bags only adds to the infant's exposure, the important message from my perspective is that any amount of breastfeeding for any amount of time is still beneficial," noted Amy Spangler, registered nurse and International Board Certified Lactation Consultant.

Amy Spangler, Registered Nurse and International Board Certified Lactation Consultant

It's worth noting that microplastics are not unique to breast milk. Infant formula also contains microplastics, meaning that regardless of how a family chooses to feed their child, microplastic exposure is largely unavoidable in today's environment. The key takeaway is that feeding your baby, whether through breastfeeding or formula, remains the priority. Worrying excessively about microplastics can create unnecessary stress for parents who are already managing demanding feeding schedules and pump maintenance routines.

As research continues to evolve, families can take comfort in knowing that small, practical adjustments to storage and heating practices can meaningfully reduce microplastic exposure without requiring major lifestyle changes. The goal is not perfection, but rather informed, manageable steps that fit within the realities of modern parenthood.