Saturday, April 1, 2023

Is it safe to microwave food in plastic containers?

Styrofoam is safe for microwaving. Bisphenols and phthalates are not. Follow many common–sense do's and don'ts when using plastics in microwave ovens.

Executive Summary

Many plastic containers come with ‘microwave safe’ tag. But how safe are they for microwaving foods in them?

Plastics cannot release dioxins into foods because they don’t contain any.

Bisphenols are used for making hard plastics. Bisphenol A is not safe for warming foods. Neither is the newer Bisphenol S. Phthalates are used for making soft and flexible plastics. They can leach into foods, too. Bisphenols and phthalates mimic human hormones, leading to reduced fertility, cancer, obesity, and growth retardation.

Styrofoam or thermocol is safe for microwaving.

The procedure, used in certification for the ‘microwave–safe’ tag, will tell you when and why not to blindly use such containers for microwaving.

The article gives guidelines about the right ways to use various types of plastic containers in microwave ovens.

One modern day activity has no parallel in our history: Microwaving food in plastic containers.

Is it safe to microwave food in plastic containers? Yes and No. Yes, if you understand how potential harm can be caused. No, otherwise. This is even more important in developing countries, where safety rules are more lax than in developed countries.

Problems with food grade plastics


There are pseudo–scientific messages circulating around the internet, which claim that plastics release dioxins into food on heating.

Dioxins are cancer–causing and hence, should be avoided. However, plastics do not contain any dioxins. So, they cannot release any into the food stored in them.

Dioxins are created only when plastics are burned. So, as long as you do not burn any food in the plastic containers, there is no fear of dioxin contamination, and concomitant cancers.

So, avoid flambéing foods in plastic containers. Of course, the real flambéing procedure involves very little burning time.

Also, do not barbecue food, while it is in a plastic container. Once again, one really cannot do any barbecuing that way. But these are the only possible ways you can get dioxins into your foods.


There are certain synthetic chemicals that are used in the making of various types of plastics. Two of the common ones that can come in contact with our foods are Bisphenols and Phthalates.


Bisphenols are used in making hard plastics, such as polycarbonate plastics and epoxy resins. The rigid plastic containers and bottles used for storing food and beverages are made with polycarbonate plastics. Epoxy resins are used to line the inside of metal food cans and bottle tops.

Bisphenol A (BPA) is the most commonly used bisphenol. It was used earlier in making the hard plastic containers. However, after an outcry about its side effects, the manufacturers started using Bisphenol S, instead of Bisphenol A, for use in plastic bottles. Unfortunately, the toxicity profile of Bisphenol S is similar to that of BPA. Additionally, the linings of metal cans are still done using BPA.

If foods or drinks kept in such containers are heated in a microwave, some BPA or Bisphenol S can leach into the food.


Phthalates are used to make soft and flexible plastics. However, if foods are microwaved inside such plastic wrappings, there is a chance of phthalates leaching into foods.

Problems with plasticizers

Both, bisphenols and phthalates, mimic the action of human hormones. So their presence in the food may falsely trigger the body to act as if certain hormone was released in it. Such products are called Endocrine Disruptors, and cause hormonal problems.

The Endocrine Society recently released a statement saying that endocrine disruptors are a cause of obesity, diabetes, problems with male and female reproduction, thyroid problems, breast and prostate cancers, and neurological problems.

Bisphenols reduce fertility, and lead to some kinds of cancerous growth. They have been associated with growth retardation in fetuses and conversion of normal cells into fat cells, leading to obesity. They also affect the working of the pancreas.

Phthalates cause inflammation and insulin resistance (that can lead to diabetes), and retard male fetal reproductive development.

Thermocol (styrofoam)

Thermocol (styrofoam) containers and cups are safe for using inside the microwaves.

Microwave–safe plastics certification

Many plastic containers carry a label saying ‘microwave–safe’. However, before using such containers for heating food in microwave ovens, it is important to note the procedure used for getting that label.

The certification label for ‘microwave–safe’ use is given by the Food and Drug Administration (FDA), USA. The FDA decides on the standards and specifications, and asks container manufacturers to perform certain tests. Before approval, it reviews the test data.

The tests measure the leaching of chemicals from plastic into food at temperatures that the plastic encounters during ordinary use. The tests estimate the ratio of plastic surface area to food, how long the container is likely to be in the microwave, how often a person is likely to use the container, and how hot the food can get during microwaving. The tests also measure the leaching for different kinds of foods, such as fats, edible acids, etc.

The reference standards include the per kg leached amount that causes harm to laboratory animals over the product’s lifetime. The ‘microwave–safe’ products can leach a maximum allowable amount of 100 to 1000 times less than this number.

Note the phrases in bold above. As you can see, these are assumptions about normal, regular, estimated, likely, and lifetime usages. If you use your container beyond these normal situations, your container may not be safe for microwaving.

Thus, ‘microwave–safe’ does not mean blanket safety for microwave use. Use discretion and common sense.

Actionable Tips

  1. Don’t keep food wrapped inside plastic cling–wrap films when heating in a microwave oven.

    Remove foods from wrapping films and place on microwave–safe plates before heating them.

  2. Be more careful when heating meats and cheese.

    Don’t use plastic containers to heat fatty substances.

  3. Don’t store hot beverages in plastic storage jars and mineral water bottles.

    Do not put these containers and bottles in microwave ovens.

  4. Styrofoam or thermocol is safe for microwave use.

    Cups of styrofoam can be used for warming coffee, tea, or cup noodles.

  5. Avoid BPA– or BPS–plastic containers for heating.

    Bisphenol–A and Bisphenol–S, both can leach into foods, when heated.

  6. Use glass or ceramic containers for heating.

    Use common sense and discretion. Err on the side of caution, when you are not sure.

  7. Do not reuse single–use food containers.

    Take–out food containers are to be discarded after a single use.

  8. Replace plastic containers often.

    Don’t use containers for more than 2–3 months.

  9. Avoid rough scouring substances, when scrubbing or washing plastic containers.

    Use liquid dishwashing liquids.

Here is an article on this website about: Various food–grade chemicals and how they affect children. Some of these are used in plastics that come in contact with our foods.

First published on: 22nd September, 2017

Image credit: Lisa Fotios from Pexels


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