Microwave oven - friend or foe? - Building Biology
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Microwave oven – friend or foe?

Microwave oven – friend or foe?

Over the years, I have often been asked about my opinion on microwave ovens as a way to heat food. So here it is…

How do microwave ovens work?

Microwave ovens use radio/microwaves (frequency of 2,450 Megahertz) to make the water molecules in the food vibrate (>2 billion times per second). This movement produces friction which heats the food.

What are the health effects?

There are two issues here – the impact on the food, and the radiation emitted from the oven itself.

Impact on the Food

  1. Scalding and burning may occur as a result of overheating foods beyond their natural boiling point, removing hot items or created from hotspots in the food (eg jam donut which is luke warm on the outside and much hotter in the centre)
  2. Bacterial growth in the food as there maybe cold spots from uneven heating
  3. Microwaving food in plastic is strongly not recommended as all plastics impart chemicals (hormone disrupting chemicals such as phthalates and BPA, toluene, benzene, acrylamide…. ) and/or metals such as antimony (if PETE or number 1 plastics are used) into the food the hotter they become
  4. Many microwaveable packaged foods such as popcorn are lined with PFOA – a suspected carcinogen – which has been found in the blood of most adults tested (it is commonly used in non-stick cookware and water proofing applications)
  5. There is conflicting and limited evidence as to its impact on the ‘vitality’ of the food with much of the research emanating from the Russian investigations – the original document of which I cannot find. Allegedly heating meat may form d-Nitrosodiethanolamine (a known carcinogen), destabilise proteins in dairy products, form radiolytic compounds and create free radicals in root vegetables amongst a list of many other things most of which cannot be repeated in scientific studies. For more detail about this refer to Phillips and Wikianswers. On the other hand, the authorities cannot prove conclusively that microwaving food does not cause these effects, so as a mum and naturopath, I would err on the side of caution.
  6. Reduces the nutritional value of the food – loss of antioxidants. Interestingly a study conducted on broccoli concluded that all cooking treatments apart from steaming, caused significant losses of chlorophyll and vitamin C and significant decreases of total soluble proteins and soluble sugars (Yuan et al, 2009).
Many BPA-free plastics tested released chemicals into the food with greater oestrogenic activity than the BPA containing plastics (Yang et al, 2011)

Radiation emitted from the oven

The oven itself emits three types of electromagnetic fields: electric field (minimal), magnetic field (can be high from the digital clock and also where the transformer is located) and radio/microwaves. The electric and magnetic field (from the digital clock) will be present even when the microwave oven is not heating. The magnetic field will typically increase beyond 100mG when the microwave oven is in use (4mG is associated with a doubling in the incidence of childhood leukaemia) and will drop off to back ground levels within one metre (inverse square law).

Apart from the fact that the World Health Organisation has classified radio/microwaves and magnetic fields in 2011 and 2002 respectively as “possibly carcinogenic to humans”, the health effects arising from exposure to these frequencies are described in my book – Healthy Home Healthy Family. However, unlike the pulsing nature of the radio/microwaves used in the telecommunications industry (mobile phones and Wi-Fi), the microwave oven uses continuous wave fields so the biological effects are not likely to be as bad.

A common misconception is that the mesh in the door is designed to prevent the microwaves leaking. All microwave ovens (even new ones) I have tested, emit radiation to varying degrees through the viewing glass (door).  The Australian/New Zealand Standard for microwave ovens permits microwave leakage ‘at any point 50mm or more, to not exceed 50 watts per square metre’. This is 5 million times higher than the maximum level of 10 microwatts per square metre permitted by building biologists. This is likely to be much higher if the door seals are damaged or if the door is damaged in any way. So don’t stand in front of the oven when it is in use!


  • Heating plastics in a microwave oven imparts chemicals and in the case of PETE (number 1 plastics) metals into the food.
  • It is one of the most common causes of burns in children.
  • There is inconclusive evidence about its impact on the vitality and nutritional content of the food.
  • The oven emits radiation which may (if you stand within a metre of it) expose you to harmful forms of radiation.

My Conclusion

Microwave ovens are a great way to sterilize objects such as wet dishcloths/sponges (1 minute) and baby bottles, but should be avoided (or used very sparingly) as a way to heat food. A toaster oven is a better alternative.

If you intend to continue to use a microwave oven:

  1. Do not stand within 1 metre in front of it whilst it is heating as the radiation will drop off significantly within a short distance
  2. NEVER ever heat plastics or cling wrap as all plastics leach resins the hotter they get (even the microwaveable plastics). Instead use microwaveable glass (pyrex), ceramics/glass or ceramics
  3. Avoid ‘microwaveable packaged foods’; instead remove the packaging and place in microwaveable glass or ceramics instead
  4. Never use foil or any metal inside the microwave oven
  5. Never operate the oven when empty
  6. Ensure the door seals are in tact, the hinges are in good order and ensure  there is no damage to the door and that it fits securely
  7. Clean the oven with a damp microfibre cloth to which you have added a couple of drops of a mild dish liquid (do not use abrasive cleaning pads)
  8. Always follow the manufacturer’s guidelines


Phillips and Phillips. nd. Microwave oven and microwave cooking overview.

Yang, CZ et al. 2011. Most plastic products release estrogenic chemicals: a potential health problem that can be solved. Environmental Health Perspectives. 119(7): 989–996.