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Microwave safe plastics - How safe are they?

Imagine it’s a cosy Sunday and you are waking up late after a well-deserved sleep-in. You don’t feel like cooking and you remember that you still have plenty of leftovers from ordering in on Saturday night. Feeling relieved that you only have to heat up the food, you pull out the take-out boxes of food from your refrigerator and you are ready to toss it in your microwave, thinking to yourself, “Thank God for technology!”. But the responsible adult in you pops up asking you to check if the plastic takeout box is safe to use in the microwave oven. So, you examine the box to check for any signs or labels which indicate the box can be used in a microwave oven. You spot one of the icons in image 1 on your takeout box. And you go back to feeling assured that you can enjoy a safe hot meal. Now here is the golden question - are plastics safe for microwave use and are ‘microwave safe’ plastics actually safe for health?


Image 1: Labels indicating microwave-safe containers

Plastics are supposedly a wonder material known for their strength and toughness, durability and flexibility and consequently, its unique ability to hold liquid. While plastics are usually considered poor conductors of heat and electricity, they are not absolutely immune to them. Plastics, when exposed to high temperatures for a long period, can be altered in form, shape, etc. But that’s not the only concern. When exposed to heat for a prolonged period, even if it’s sunlight, plastics undergo thermal degradation wherein the chemical bonds are broken down. Even if it’s not visible to our naked eyes, there is a lot going on!

When heat breaks down the chemical bonds in any plastic product, the chemicals and additives used to make plastics 'wondrous’ are released, thereby leaching into the substance you have stored in your plastic container. This is exceptionally dangerous as these chemicals are hazardous to health. Despite the lack of transparency in what kind of chemicals or group of chemicals are employed in the manufacturing of polymers and plastic products, UNEP’s studies show that there are more than 13000 chemicals associated with plastics and plastic production. Out of these 13000, there is sufficient data only for 7000 chemicals, and of these 7000 chemicals, about  50% have been identified as chemicals of concern - meaning hazardous to human health and the environment. This is why many experts repeatedly advise to not use plastics to store hot food or even drink water from a  plastic bottle left  in a hot car. When PET bottles in cars are exposed to sunlight, the UV radiation breaks down the chemical bonds in it,  leaching  a variety of chemicals into the water, making it dangerous for consumption.

Now that we are familiar with the affairs of plastics and heat, one might wonder that it is ‘regular plastics’ that may not be equipped to withstand heat and therefore  not safe to use in a microwave oven. But what about plastics which are labelled as ‘microwave-safe’? They should be able to withstand heat and therefore be safe for consumption, right? Well, right and wrong! Right that microwave-safe plastics can withstand heat and wrong that they are safe for consumption. While this is the answer in a nutshell, a slice of science could help us understand the facts better.

How does a microwave work? Inside a microwave oven, a device called magnetron produces microwaves, which are a form of electromagnetic radiation. The microwaves bouncing off the metal interiors of the oven cause the water molecules in your food to vibrate. This vibration of water molecules causes friction between them and produces heat as a result. This is how you get a hot meal in under 30 seconds. A label which indicates that a plastic product is ‘microwave-safe’ only means that the plastic product will retain its original shape and form and can withstand the temperature enough to not melt. But the ‘microwave safe’ icon has nothing to do with whether or not it is safe for human health, as the leaching of chemicals continues to happen even when you use a ‘microwave safe’ plastic in the oven. 

To make plastics viable for a wide range of applications, many chemical additives are used in making a product. Two of the most common chemicals added to many plastic products are Bisphenol A, aka, BPA and Phthalates. BPA is added to make plastics harder and phthalates are added to make it flexible and durable. BPA and phthalates are well known to be endocrine disrupting chemicals and have been associated with a plethora of health impacts such as infertility, thyroid diseases, cancer, early puberty, neurobehavioral disorders, metabolic dysfunction, etc. Earlier, in the 1960s BPA was used commonly in food packaging and other consumer goods including baby bottles. In consideration of the furore over hazardous health impacts of BPA, governments gradually banned BPA in some products. 

Most food delivery or takeout boxes are type no. 5 (PP) aka polypropylene. PP plastics are usually claimed to be ‘microwave safe’ but we know by now that ‘microwave safe’ simply means it's safe for the plastic box so that it can withstand the heat without  melting. PP plastics are also advertised as safe for microwave use because they are BPA free. However, BPA free plastics are still dangerous as they contain alternatives such as bisphenol S or bisphenol F, which also leach hazardous chemicals. Also, BPA free plastics can still contain phthalates which are also endocrine disrupting chemicals, as mentioned above. 

There could arise a misconception that using a lid to cover your food in a microwave oven could protect the integrity of the container and mitigate the leachate damage to some extent. However, if the microwaves have heated your food, they have certainly heated the plastic too. Refraining from using plastic containers irrespective of their labelling (microwave-safe or not) and switching to glass or ceramic containers is a much safer option.  It is also important to not use plastic film to cover the food in the microwave oven when you’re using a glass or ceramic container, as the condensation underneath the plastic film or lid could result in chemical leachate directly dripping into your food. So, (for the love of health!), next time you need to microwave something, please bear in mind that when a plastic container claims to be microwave-safe, it’s safe for the container but not for your health.

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