Human Milk Warming and Best Practice Improvements

Jenny Murray, BSN, RN / April 2018


“I’m just going to warm this milk really quick.”

I’m here to tell you you’re not “just warming milk.” Milk warming is a process that is so simple, and yet so profound in the Neonatal Intensive Care Unit (NICU).

Think about what we are doing when we properly warm human milk. Think about the benefits the baby will reap based on proper warming. Proper warming helps preserve valuable human milk properties, which in turn decreases many risks to NICU infants.

The “old” way

I, myself, used cup and water as a NICU nurse. I thought about the harmful effects that “too hot” water had on human milk, but I was also concerned about burning myself with water from the hot water spigots (we’ve all done it or known someone who has!).

Thankfully, there is equipment and research that supports safely warming human milk. More research is still needed, but we do know that the way human milk is warmed in the NICU matters, and varies GREATLY!

Human milk is a balance

Let’s start by remembering that human milk is a fresh, living nourishment containing many antioxidant, antibacterial, prebiotic, probiotic and immune-boosting properties, in addition to proteins, essential fats, enzymes, and hormones; many of them are uniquely human-coded. We know that proper heating can preserve these essential components. Fats are the main energy source of human milk, comprising 45-55% of the total calories.¹

Best practices

One research study showed that there was up to a 40-degree difference in water bath temperatures.  When one nurse says it feels “good,” the next nurse might say is too hot or cold. “Testing” water bath temperatures by touch is very subjective, and therefore unreliable.

There are also well documented risks associated with using water to warm milk in the hospital setting.

So how should we warm?

Let’s discuss two important components of warming human milk:

  1. Ensure the essential components remain intact throughout the warming process

How hot is too hot? How cold is too cold?

We know that human milk is a complex, bioactive living fluid that is vulnerable to temperature changes. When warmed properly, important components – including Secretory IgA, lactoferrin, lysozyme, white blood cells, and probiotic bacteria – remain intact. However, when human milk is overheated – for example, to 144 degrees Fahrenheit – immune proteins are decreased while beneficial bacteria and white blood cells are destroyed. Studies have shown that the higher the temperature and longer the exposure to heat, the greater the destruction of the beneficial properties of human milk.²

Conserving calories in order to deliver a higher fat content to a sick, preterm neonate is imperative. We know that one of the biggest challenges in the NICU is growing our babies. With that said, warming milk to body temperature will not only help with feeding tolerance, but will help an infant to conserve the calories they would otherwise burn by having to heat the milk themselves.³  The Human Milk Bank Association of North America (HMBANA) recommends warming milk to body temperature.⁴

  1. Ensure we do not subject valuable human milk to contamination that could otherwise be eliminated

There are a variety of options to warm milk.

Keep in mind our focus is on the neonate in a hospital setting.  These patients have odds stacked against them from the very beginning.

The CDC recommends removing all contaminated water or fluid environmental reservoirs (e.g., in equipment or solutions) wherever possible.⁵  For 40 years, hospital tap water has been identified as a potential source of nosocomial infections from bacteria and other contaminants. Water systems are well recognized as potential reservoirs for healthcare-associated infections.⁶  As recently as 2009, 23 strains of Pseudomonas aeruginosa were found in the water supply of a children’s hospital in the US.⁷

Implementing a waterless warming system that safely heats to preserve essential components of human milk eliminates the possibility of contamination that can be detrimental to the most vulnerable patients.

Going forward

Next time you warm a human milk feed, think about the difference you are making in what you provide. Has it been warmed within parameters that safely preserve the essential components? Is it being provided warmed whether by bottle or gavage feeding? Has the risk of contamination been minimized by eliminating the use of water to warm?

These questions can help your team move forward to an improved milk warming process.

After all, it’s not just human milk – it’s medicine for the sick, preterm babies you care for.


Learn more about waterless milk warming with the Medela Waterless Milk Warmer and the Medela Guardian Warmer.



  1. Bransburg-Zabary S, Virozub A, Mimouni FB (2015) Human Milk Warming Temperatures Using a Simulation of Currently Available Storage and Warming Methods. PLoS ONE 10(6): e0128806.
  2. Czank C, Prime DK, Hartmann B, Simmer K, and Harmann PE. Retention of the immunological proteins of pasteurized human milk in relation to pasteurizer design and practice.  Pediatric Research (2009), 66(4):374-379.
  3. onzales I, Duryea EJ, Vasquez E, Geraghty N. Effect of enteral feeding temperature on feeding tolerance in preterm infants.  Neonatal Network. (1995), 14:39-43
  4. Jones F (2011) Best Practice for Expressing, Storing and Handling Human Milk in Hospitals, Homes, and Child Care Settings. Human Milk Bank Association of North America; 3 edition
  5. Guidelines for environmental infection control in health-care facilities.  In:  (HICPAC) HICPAC, ed.: MMWR; 2003: 1-42
  6. Rhodes J. Best Practices for Warming Human Milk in a Hospital Setting.  The Journal of Perinatology-Neonatology.  (2012), 25(3):7-9
  7. Jefferies J.M.C., Cooper T., Yam T., Clarke S.C.  Pseudomonas aeruginosa outbreaks in the neonatal intensive care unit – a systematic review of risk factors and environmental sources.  Journal of Medical Microbiology. (2012), 61:1052–1061


About the Author

Jenny Murray, BSN, RN, began her career 18 years ago as a neonatal nurse in neonatal intensive care. She has since served in a variety of nursing leadership roles within the NICU. Her experience in those roles has driven her love for education and research, especially educating and supporting clinicians in the advancing, innovative world of neonatology. Jenny currently works as a Clinical NICU Specialist for Medela LLC.