Are Microwaves Safe? | Debunking Molecular Myths

Microwave ovens are a convenience dream, making meals in minutes and keeping washing up to a minimum. But how do microwaves cook our food? This mystery has led some to question ‘’Are microwaves safe?’’.

As one of the most significant cooking inventions of the 20th century, microwaves turned cooking dinner from an hour or two of slaving over a stove into simply putting food in a box, setting the timer and waiting for that notorious ping! But despite being a common sight in kitchens since the 1970s, conflicting opinions and an abundance of misinformation still surround the microwave oven today. This is partly because many of us who own a microwave don’t know how it actually cooks our food - so here are 5 of your biggest questions about microwaves, answered. 

1. How do microwaves work?

Physicist Percy Spencer accidentally discovered microwave cooking in 1945, when the chocolate bar in his pocket melted whilst working with a microwave-emitting radar.¹  Since then, microwave ovens have revolutionised easy home cooking - but how do they work? 

A good place to begin is with their name. Microwaves are a family of electromagnetic waves, part of the electromagnetic spectrum. This spectrum includes other familiar names like X-rays, radio waves and visible light. Each type of wave in this spectrum varies in how much energy it has, ranging from very low frequency, low energy radio waves to extremely high frequency, high energy (and highly dangerous) gamma rays.² Microwaves are fairly low-energy (and therefore fairly safe) electromagnetic waves, but they still contain enough energy to heat up and cook our food.

When microwaves come into contact with the water molecules in our food, they make those water molecules vibrate. These vibrations generate energy, which in turn generates heat, and it is this heat that cooks our food.³ Microwave ovens create a concentrated and targeted blast of microwaves, causing the water molecules locked inside food to vibrate incredibly fast and quickly heat up, cooking your dinner in minutes.

2. Does microwaving food destroy nutrients? 

Yes and no. Many people worry that microwave ovens damage our food, destroying its nutrients during the cooking process. Sadly, nutrients are lost in all forms of cooking: whether over a stove or in the microwave, heating food up breaks down some molecules and lowers the nutritional value of our food.⁴ It’s an inescapable trade-off for killing any harmful microbes lurking in your food that could make you sick. 

However, the faster you heat up your food, the less time there is for nutrients to break down - meaning microwaves may actually have the advantage over traditional cooking when preserving the nutrients in our food.⁵ Take broccoli, which contains the beneficial sulphur-containing compound glucosinolate, as an example: when boiling broccoli, a lot of this beneficial glucosinolate is lost to the surrounding water, but much less is lost when cooking broccoli in the microwave due to the shorter cooking time.⁵

Read more about how cooking changes the nutrients in our food.

3. Do microwaves cook your food all the way through?

Not always. Microwave ovens bombard your food with microwaves, which then bounce all around inside until they are absorbed by your food. However, this happens randomly and unevenly, so you’ll usually find a spinning fan and a rotating dish inside microwaves to distribute this energy more consistently and ensure your food cooks as evenly as possible. 

Despite these adjustments, microwaves can still only penetrate food as far as 1-1.5cms,⁶ as their energy runs out quickly once they start interacting with the water molecules in food. This usually isn’t a problem, since the middle of whatever you’re cooking gets heated up through conduction instead, but it’s worth being careful. For example, cooking meat in a microwave can be risky as it won’t necessarily cook evenly all the way through: even while the outside is burning, the middle parts might actually be underdone.

Tip: Be careful when cooking ‘sealed’ foods with a high water content (like eggs and potatoes) in a microwave oven. Microwave energy turns water into steam, and if that steam becomes trapped inside the food, the pressure will rapidly build until it is released by an explosion⁷ - much to the dismay of both your microwave and your lunch. Always pierce the skin of your potatoes a few times before cooking to prevent this!

4. Do plastic containers “leak” into microwaved food?

It depends on the plastic. If plastic becomes hot enough to break down, it can leach harmful chemicals (such as the plasticisers bisphenol-A (BPA) and phthalate, which can mimic hormones in your body) into your food, affecting your health.⁸ So, when putting plastic in the microwave, caution is your friend.

Luckily, plastic is not a single, homogenous substance, and some plastics (such as the plastic trays from supermarket ready-meals) are made specifically with microwaves in mind. As long as you check that the plastic container you use is microwave-safe (and these days, most are), you should be fine.

Plastic wrap is actually also safe to use in the microwave, so long as it doesn’t touch the food itself in the cooking process; if it does, the heat coming off your food could cause it to melt. This precaution, that plastic wrap shouldn’t touch food during cooking, is officially recommended in the US and Ireland by their national food agencies, and EU law instructs that so long as the plastic wrap in question isn’t specifically marked as not safe, it is OK to use in the microwave.⁹ These different details between countries just show how much can vary when it comes to plastic and your food.

5. Are microwaves dangerous (or ‘radioactive’)?

No. One of the biggest misconceptions surrounding microwaves is that their energy is radioactive. This often leads to the misconception that microwave ovens are dangerous. It is true that all frequencies on the electromagnetic spectrum are a form of radiation, but just because something is classed as radiation doesn’t mean it is radioactive. 

Radioactivity refers specifically to things that produce very high energy radiation, known as ionising radiation. Ionising radiation is a wave that has enough energy to remove an electron from (or ‘ionise’) an atom.¹⁰ This destabilises atomic structures and, most importantly for humans, can damage DNA and cause cancer, radiation burns and other nasty conditions. 

Luckily, only high-frequency waves (such as X-rays, gamma rays and some ultraviolet waves²) are ionising. Low-frequency waves, such as microwaves, are not. In this respect, microwaves are harmless. In fact, due to their low energy when not confined to a small space, microwaves in the air are significantly safer than the ultraviolet light hitting your skin on a sunny day! 

If you were exposed to microwaves in large quantities, they would cause burns, but microwave ovens are carefully designed and regulated to ensure that all the microwave energy they produce is contained within the ovens themselves. So you shouldn’t use your microwave oven if it’s broken or has been modified, but otherwise, there is no reason to worry about your health when cooking food using microwaves.

Cooking with microwaves: quick, easy and safe

There we have it: five key myths about the microwave oven dispelled for you. After all these years, microwaves are still a quick, convenient and - most importantly - safe way to cook food.