I was almost eaten alive by my wife after she found out I heated our baby's dinner in a microwave.

The concern is that microwave heating is uneven and it could make a super hot spot in breast milk or formula that could burn the baby's mouth.

I don't recommend it because it's not safe. A microwave oven heats unevenly, basically from the inside out, so it's possible that the formula could be very hot in the middle of the bottle but barely lukewarm on the outside where you can feel it.

Heating breast milk or infant formula in the microwave is not recommended. Studies have shown that microwaves heat baby's milk and food unevenly. This results in "hot spots" that can scald a baby's mouth and throat.

Does heating breastmilk in a microwave for 10-20 seconds makes the milk dangerously hot compared to conventional heating?

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    I've focussed the question on a single claim. If you want to ask about nutritionally loss, please ask another question. – Oddthinking May 13 '15 at 1:04
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    Microwaving anything can cause those "hot spots", but thermal equilibrium will quickly deal with this. I don't know if this link qualifies as a reliable source, but here is a short discussion what-if.xkcd.com/131/index.html – Avrham Aton May 13 '15 at 5:57
  • Let's assume it is true. Milk is a liquid, once you take the bottle out of the microwave oven, spin it, it mixes and evens out the heat all over. I believe this can only be possible with solid jar foods. I used to microwave my babies milk and nothing ever happened to her. – Ansari May 13 '15 at 6:00
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    @Ansari if you mix the milk after microwaving, and THEN verify the temperature is less than 37 degrees C, that would be safe (from a purely temperature perspective). However, the problem is some people only feel the outside of the bottle after microwaving and misjudge and the baby gets burned. If these happens even 1 in 10,000 times that's still many babies being injured. – DavePhD May 13 '15 at 12:29
up vote 19 down vote accepted

There are local hot spots if you don't mix the milk after microwaving.

Babies really do get burned by microwaved milk; there is an actual danger the medical community is trying to prevent when giving advice not to microwave milk.

The danger is due to a combination of hot spots within the milk and the container being cooler than the milk itself. If someone just feels the outside of the container they may misapprehend the temperature of the milk, resulting in the baby being burned.

Microwave heating of infant formula: a dilemma resolved Pediatrics (1992) vol. 90 pages 412-415.

Microwave heating of infant formula is a common practice despite concerns of infant scalding....Topmost portions reached a mean temperature of 44.7 +/- 1.7 degrees C and 43.0 +/- 2.4 degrees C for all types of 240-mL and 120-mL bottles, respectively. Topmost temperatures were significantly hotter than temperatures reached at other sites. Routine mixing resulted in formula temperatures which could safely be fed to infants (35.4 +/- 0.3 degrees C and 33.9 +/- 0.2 degrees C for 240-mL and 120-mL bottles, respectively).

Risk factors for microwave scald injuries in infants. Journal of Pediatrics (1984) vol. 105 page 864-867.

An infant sustained second- and third-degree scald burns of the oropharynx from drinking formula heated in a microwave oven. The circumstances leading to the scald injuries were recreated. Factors contributing to the injury included the volume of formula, the initial temperature of the formula, and the temperature gradient between the liquid core and the bottle surface after microwave heating.

Burns associated with the use of microwave ovens. Journal of Microwave Power and Electromagnetic Energy (1992) vol. 27, pages 160-163.

burns can result from the ingestion of microwave heated food because consumers may overlook the differential temperature gradients within foods and between the food and the container.

Other related articles are:

Burns by ingestion of milk warmed-up in a microwave oven Archives of French Pediatrics 1988 vol. 45 page 439.

Aerodigestive tract burn from ingestion of microwaved food. Case Reports of Emergency Medicine (2013) article 781809.

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    The first study you quoted seems to come to the opposite conclusion, that hotspots occur, but that "Routine mixing resulted in formula temperatures which could safely be fed to infants". – Sean Duggan May 13 '15 at 14:31
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    @SeanDuggan I don't see how that's an opposite conclusion. Obviously if you mix the milk after microwaving it will all be one temperature, and if you verify that it is 37 degrees C or less you won't burn the baby. However, not everyone does that every time, and babies get burned, so it is reasonable for the medical community to advise not to microwave. People are in a rush, drunk, high, arguing and trying to take care of babies at the same time and babies get hurt because they feel the ouside of the container and it doesn't seem like the baby would get burned. – DavePhD May 13 '15 at 14:40
  • My point of view is that you state "don't microwave breastmilk" and then quote a study which says "there are hotspots, but routine mixing eliminates them". Your current edit retains that. Thank you. I understand that, from your point of view, you were quoting the study just to establish that microwaving causes hotspots, but it niggled at me that you were selectively quoting a dissenting opinion on whether microwaving formula was safe to support your opinion that it's unsafe. – Sean Duggan May 13 '15 at 14:45
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    @SeanDuggan The question asked whether hot spots occur and can be dangerous, the answer is yes. Whether it is possible to alleviate the risk posed by these hot spots is irrelevant to the question. – March Ho May 13 '15 at 17:38
  • @MarchHo: That is correct that only the first part of the summary is directly applicable. However, cutting off the summary as it is implies that the authors of the study were saying that microwaving milk is unsafe whereas their actual conclusion was that it was safe with a minor precaution. – Sean Duggan May 13 '15 at 18:23

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