With all due respect to passionate parents who type in caps "NEVER HEAT MILK IN MICROWAVE" is there any verifiable scientific study on how bad it is to heat refrigerated milk for 15-20 seconds?

Or is it just an expression of fear against unknown?
On one of the forums I've read that microwave ovens emit "sound waves" that destroy "atomic structures" that lead me to believe that it could be just one another urban myth that was spread by the media.

Two main points against mircrowaving I've read:

  1. Microwaves destroy proteins and vitamins.
    Does it?
    Destroy into what?
    Would not proteins be destroyed in the stomach anyway?
    Would conventional heating destroy it as well?
    Why is destroying bad?
    Would it destroy bad things, too?

  2. Microwave heating is uneven and it could make a super hot spot that could burn the baby's mouth a bit.
    Is there a research of the risks?
    It does not create a super hot spot in my bowl of pasta if I mix it after heating for 2 minutes.
    I understand that fat in breastmilk is not homogenised and that fat can retain heat for long.
    What if I shake or swirl the bottle for 10 seconds?
    How long the hot spot could exist?

A few studies from the 90s I have found:
http://www.ncbi.nlm.nih.gov/pubmed/8889628 - says there are no effects on B1/E/acids if resulted average heat is not higher than 60 C
[same website link] - same, no difference in B1/B6 if compared to stove top heating
http://m.pediatrics.aappublications.org/content/89/4/667.short - E.coli bacteria grows faster in microwaved milk than controlled, i.e. antibacterial qualities are reduced

Is there anything else?
I would appreciate hearing your opinion on the matter but a link to a relevant research would be way more trustworthy.

  • 3
    Tangentially related, this Skeptics Question indicates that excessive shaking can break down components in breastmilk (and includes citations to back that up). – Acire May 12 '15 at 15:16
  • In future, please do not crosspost the same (or nearly identical) questions on multiple StackExchange sites, but pick the site that is best suited to answering your question. For those interested in the relevant research, an informative sampling is at the answer to the matching Skeptics question. – Acire May 17 '15 at 18:01
  • It's not about nutrition, it's about the danger of burns. – DanBeale May 17 '15 at 18:57
  • I did not find the second paper convincing at all. There appear to be multiple discrepancies in methodology and they have not compared microwave heating to non-microwave heating, despite claiming to have shown that microwave heating is problematic. – Sam Brightman Dec 9 '18 at 12:33

Not to necro post, but I did find a study which seems to directly answer this question: https://www.ncbi.nlm.nih.gov/pubmed/8889628

Short answer is that they found no significant impact on nutritional value as long as the final temperature of the milk stayed below 60 C (140F).

Considering our target temp is 37C (98.6F) it should be no problem if you are paying attention to the temp.

One might argue that you could still end up with small pockets of over heated milk, and my answer to that would be to simply heat the milk in small increments of maybe 10 sec where you swirl the bottle in between to distribute heat and check temp.

Aside from that just be sure to use a microwave safe bottle.

  • 1
    Hi, welcome to parenting.SE! And don't worry, late posting is no problem here - only the quality of the answer matters, and answers supported by references are always a good idea. – sleske Jan 31 '17 at 14:05
  • +1 - "...simply heat the milk in small increments of maybe 10 sec where you swirl the bottle in between to distribute heat and check temp." This is what I did. Nice to see an answer with backup source! – anongoodnurse Jan 31 '17 at 18:22

Well, NHS Choices says:

Don't use a microwave to heat up or defrost breast milk as it can cause hot spots, which can burn your baby's mouth.

The American Academy of Paediatrics says:

Do not use microwave ovens to heat bottles, because they do not heat them evenly. Uneven heating can scald your baby or damage the milk. Bottles can also explode if left in the microwave too long. Excessive heat can destroy important proteins and vitamins in the milk.

Western Australia Dept of Health says:

  • Microwave ovens should never be used to thaw or heat milk.
  • The major problem with microwave ovens is that they cause uneven heating. The temperature of the surface may be a lot hotter or cooler than the rest of the milk.

And the FDA says:

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.

So the issues seem to be:

  • the possibility of 'hotspots' due to uneven heating, combined with the easy-to-burn nature of a newborn's mouth/throat, and

  • the possibility of overcooking the milk and thereby making it less nutritious.

For the other possible factors you mention, I'm with you in suspecting they're basically nonsense, but I don't have any evidence. If you want some serious debunking then skeptics.stackexchange.com may be able to help.

  • 1
    Could someone explain the "hot spots" to me? Milk is a liquid... if you shake it a bit, shouldn't that solve the hot spot problem? – Layna May 12 '15 at 13:32
  • @Layna, I would certainly have thought that stirring would solve the problem, although you'd need a sterile object to stir it with. Maybe related somehow to the risk of superheating in a microwave? – A E May 12 '15 at 13:50
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    @Layna Have you ever been in a body of water (pool, river, lake, etc) and noticed how much warmer or colder a certain area was than the rest? I do believe shaking it up thoroughly would level out the temperature, but the risk there is that people wouldn't shake it up thoroughly, or that the drop they test is a good temperature, while a hot portion of liquid remains untested. There is also the issue of the microwave breaking down the bottle plastics, leeching hormones and chemicals into the milk. – Kurt E. Clothier May 13 '15 at 0:21
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    @Layna - parents are sleep deprived and sometimes forget to shake the bottle. Shaking the bottle adds air to the milk which is something you generally want to avoid. Everyone has thinner skin in their mouths. Babies have even thinner skin. That increases the risk of severe burns. A babies mouth can experience a fullthickness burn (3rd degree burn) requiring surgery under anaesthetic almost instantly if the liquid is hot enough. Multiple health agencies in different countries strongly recommend against heating milk in microwave ovens. – DanBeale May 17 '15 at 19:04
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    great response. +1 for pointing to skeptics. However, I will say I'm pretty confident that the concerns of the OP are non-issues; I just don't have the time to write a full skeptics-worthy answer to prove it. – dsollen Jul 15 '15 at 15:56

Recent studies recommend a heating temperature of no more than 37C (98.6F) as fat content, free fatty acid concentration, and total antioxidant capacity were significantly lower at higher temperatures. This study also recommended thawing in the refrigerator rather than microwave.

The trick is only heating it to normal body temperature (less is fine, too). You might invest in a food thermometer to test the temperature of heated breast milk until you figure out how long and at what level you should be using your particular microwave. In the study, they used a 30% setting, so that's a place to start.

As mentioned in other posts, hot spots can be reduced by allowing the milk to stand after warming.


Chan, J., Gill, G., & Chan, G. (2011). The effects of different thawing methods on the nutritional properties in human milk. Journal Of Neonatal -- Perinatal Medicine, 4(4), 341-346.


Microwave ovens should never be used to cook anything- except, possibly, for water-, due to a process called "structural isomerism" (among other reasons), which, at the very least, reduces or eliminates any health benefit of such components as amino acids/proteins/enzymes, and other compounds, and at worst, actually converts them into toxic substances. This is known to occur in infant formula as well as breast milk (http://www.greenhealthwatch.com/newsstories/newschildren/children-dont-microwave-babys-breastMilk.html). There are a list of substances in infant formula (ones that are healthy before they go in the microwave) that convert into neuro-, hepa-, and renal- toxic isomers of the respective compounds.

To directly answer your questions:

  1. Yes, microwaves destroy proteins, enzymes (proteins) and nutrients; and the more complex they are, the more susceptible they are to degradation. I am not up on my biochemistry, but I understand that proteins are essentially constructs built up from any number of branched and chained amino acids. They are extremely large and complex molecules, and the shape of the whole protein matters. When it is heated, this molecule begins to "flatten and unravel", rendering it unable to fulfill its purpose (whatever that may have been), and breaking it down into its individual components. This occurs with conventional cooking as well, but since microwaves cook materials by directly exciting the molecules (and water within foods), it happens very quickly and changes occur even with very short-duration (warming up) exposure. What it breaks down or converts into depends on what it was. Many complex molecules will break down into constituent parts, some amino acids will change shape into inert, or even highly toxic "isomers" (compounds with the same chemical formula, but with a different molecular shape). There is not a direct relationship to the time for which the food is exposed, as these reactions start immediately and occur very rapidly.
  2. Uneven heating is really easy to fix, and really easy to test, and I am skeptical that this is really even a problem, since convection currents will make short work of distributing heat in a fluid. I don't give my 3-year-old food right out of a pot or pan, why would a microwave be any different, and with an infant on top of that. Let it rest a couple minutes, thoroughly mix/swirl/(probably not shake), and test. If you are really worried about uneven heating (and assuming you believe everything else to this point is hogwash), try this.

Garlic anti-carcinogenic activity and microwaves
Microwaving broccoli
Protein unfolding

There are quite a few, but the actual studies are both harder to find than opinion, and a lot harder to digest due to the jargon, but it is worth the time to find and understand (at least at a basic or abstract level) if you are interested in the topic.

  • 1
    Downvote: greenheathwatch.com is a poor information source as it includes a number of articles which make claims that have been specifically disproved. – James Snell Jul 17 '15 at 11:36
  • Couldn't find a link to the actual study, so I settled on what I could find. Could you provide a (reputable) counter to the actual point/statement instead of attacking the source of (just one bit) of the information? – zugzwang Jul 17 '15 at 14:57
  • Alteration of proteins is a normal part of cooking: when you heat them up, they unfold, cross-link, break up, and undergo other alterations. There's nothing special about microwaves here, and in fact, it's generally a good thing: these changes make the proteins easier to digest. Isomerism is a real thing, and heating can sometimes cause chiral molecules to switch from one configuration to the other, but again, there's nothing special about microwaves. – Mark Jun 10 '17 at 19:36

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