Is it Safe to Warm Human Milk? How Warm Does it Need to Be Before Mixing in Gelmix?

Properly stored human milk maintains many of its unique qualities and continues to be a preferred alternative when freshly expressed milk is not an option. Warming stored breast milk to body temperature is accepted and even encouraged for some neonatal digestive systems, however most experts agree that to preserve the unique bioactive attributes of human milk, ideally it should not be warmed more than 104°F (40°C). In cases where mother’s own milk is not available, donor human milk is often heat treated over 140°F to make it safe for consumption.

Heat treatment of human milk has been studied largely due to the necessity to pasteurize donor human milk. While macronutrient value of human milk is not significantly affected, high heat does impact bioactive properties of breast milk. Despite the impact pasteurization has on some of the bioactive properties of donor milk, it is still considered an acceptable and even preferred alternative when mother’s own milk is not available. Warming to 110-120°F has less of an impact on the bioactive properties than pasteurization, and most of the beneficial properties of human milk are still present even after warming up to 120°F.

In order for Gelmix Infant Thickener to effectively thicken, the milk needs to be at least body temperature, around 98.6°F. While Gelmix does thicken freshly expressed milk at body temperature, various factors, like the temperature of the room and time it takes to express, can result in a cooler liquid when mixed. If thickening is recommended to reduce spit-ups, the milk does not need to be fully thickened before swallowing, and Gelmix will still be effective when mixed with freshly expressed milk. 

However, if thickening is recommended as a diet modification for an infant with dysphagia, the milk needs to be thickened BEFORE swallowing. Using freshly expressed milk may be too cool, and it is critical that the milk be properly warmed before mixing in Gelmix to achieve desired thickness. Gelmix thickens liquids BEST between 96-104°F. Mixing at this temperature achieves a thicker consistency and requires less product to thicken up than if lower temperatures are used. 

The IDDSI flow test is a practical measure of flow rate with internationally accepted categorization. Due to the impact temperature can have on flow rates, we recommend utilizing this simple tool to confirm the recommended flow is being achieved before serving in these critical settings. Always flow test at serving temperature.


Bransburg-Zabary, S., Virozub, A., & Mimouni, F. B. (2015). Human milk warming temperatures using a simulation of currently available storage and warming methods. PLoS One, 10(6), e0128806.

Lawrence, R. M. (2022). Host-resistance factors and immunologic significance of human milk. In Breastfeeding (pp. 145-192). Elsevier.

Meng, F., Uniacke-Lowe, T., Ryan, A. C., & Kelly, A. L. (2021). The composition and physico-chemical properties of human milk: A review. Trends in Food Science & Technology, 112, 608-621.

Ng, V., Bogaardt, H., Tzannes, G., Collins, S., & Docking, K. (2021). Thickened Formulas Used for Infants with Dysphagia: Influence of Time and Temperature. Dysphagia, 1-10.

Quigley, M., Embleton, N. D., & McGuire, W. (2019). Formula versus donor breast milk for feeding preterm or low birth weight infants. Cochrane Database of systematic reviews, (7). 

Uygur, O., Yalaz, M., Can, N., Koroglu, O. A., & Kultursay, N. (2019). Preterm infants may better tolerate feeds at temperatures closer to freshly expressed breast milk: A randomized controlled trial. Breastfeeding Medicine, 14(3), 154-158.

Updated 05/08/2023