Warming Human Milk: Details Matter

Jenny Murray, BSN, RN / March 2021

Learning All About Warming Human Milk for Patients

As a NICU nurse myself, I did not think a lot about warming milk. If your patient was stable enough to begin feeds, monitoring the tolerance of the feeds and respiratory status required greater amounts of focus – or so I thought. Actually, an infant who receives human milk (HM), especially mothers’ own milk (MOM), is receiving some of the best medicine. How this is delivered is crucial to maintaining all of the essential components that are critical to reducing morbidities and mortality in this very vulnerable population.

Critical areas of focus when warming human milk are:

  1. Controlling temperatures to maintain essential components of HM
  2. Eliminating the risk of waterborne pathogens

I remember hearing, “I’m just going to warm milk real quick” quite often. I hope I can help you look at warming differently. The benefits of using a warming device designed to reduce potential sources of bacteria while safely heating to maintain all the essential components of human milk can provide lifelong benefits to your patients. Details matter.

So, How Does Temperature Affect the Essential Components of Human Milk?

HM is a complex, bioactive, living fluid that is vulnerable to temperature changes. If HM is warmed to body temperature (but no more than 104 degrees Fahrenheit), then important components – including secretory IGA, lactoferrin, lysozyme, white blood cells, and probiotic bacteria – remain intact. However, when human milk is over heated – 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 HM.

HM contains 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 HM, comprising 45 - 55% of the total calories. Growth is a critical factor within the NICU. Doing our part to preserve precious calories can help to combat one of the biggest issues we see in the tiniest patients – growth.

Why Does Eliminating Water Matter When Warming Human Milk?

The CDC recommends removing water whenever possible in healthcare settings to reduce the risk of waterborne pathogens. One of the most common waterborne pathogens is Pseudomonas aeruginosa.

In 2019, the CDC reported multidrug-resistant Pseudomas aeruginosa as a “serious threat” level with more than 32,000 reported cases in hospitalized patients in 2017, an estimated 2,700 deaths, and $767M estimated attributable healthcare costs that same year alone! The CDC also states that “moist environments and aqueous solutions in healthcare settings have the potential to serve as reservoirs for waterborne microorganisms.” They cite continued infection control as a preventative strategy.

There are a multitude of research articles that support removing water to warm and incorporate “dry warming devices” when available. A published report in Clinical Infectious Diseases in 2016 stated hospital water and water-related devices can serve as a reservoir of waterborne pathogens in healthcare settings. They go on to report that the hospital environment may allow for contamination by waterborne pathogens because water temperatures are suitable for bacterial growth and stagnant water can lead to corrosion and biofilm formation. “Nosocomial infections caused by waterborne pathogens include Pseudomonas and Legionella. Particular patients at risk are premature infants in the NICU.”

It is also important to remember these waterborne pathogens are transmitted via contact, ingestion, and aerosolization. Contact transmission may be via healthcare workers’ hands to patients, direct patient contact, or equipment contamination. A published article in the Journal of Infectious Diseases titled, “Finding the Sources of Septicemia at a Neonatal Intensive Care Unit: Newborns and Infants Can Be Contaminated While Being Fed” stated “moisturized media and liquid materials are especially important sources of pathogenic microorganisms.”

Remember, Details Matter!

I challenge you to think about how you are warming human milk. It’s not “just another feeding”. Each feeding of human milk is another dose of “vital medicine” that, through research, is shown to reduce morbidities and mortality within this very fragile patient population. Implementing a waterless warming system that safely heats to preserve essential components of HM and eliminates the possibility of waterborne contamination is key.

As a NICU nurse, I know you are astute at ensuring consideration of every intricate detail that can make a substantial difference in a patient population that is set apart from the rest. You recognize you have been entrusted to a parents’ most precious gift – their sweet, vulnerable baby. Details matter.


  1. 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.
  2. 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. https://doi.org/10.1371/journal.pone.0128806
  3. Centers for Disease Control and Prevention. (2003 –updated 2019) Guidelines for Environmental Infection Control in Health-Care Facilities.  Recommendations of CDC and Healthcare Infection Control Practices Advisory Committee (HICPAC).
  4. Kanamori, H., et al. Healthcare Outbreaks Associated With a Water Reservoir and Infection Prevention Strategies. Clin Infect Dis. 2016 Jun 1;62(11):1423-35. doi: 10.1093/cid/ciw122.

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.

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