Microwave ovens have been a part of many American households since the mid-1970s and most users quickly learned to keep aluminum foil and metal utensils out of this appliance. The burst of sparks was an easy clue, and the ensuing fire and ruined microwave were the final answers.
Cooking fires are the leading cause of reported house fires. According to a 2020 report from the National Fire Protection Association (NFPA), between 2014 and 2018, firefighters responded to an annual average of 172,900 home structure fires started by cooking activities. The NFPA says these fires caused an annual average of:
- 550 civilian deaths
- 4,820 reported civilian fire injuries
- More than $1 billion in direct property damage per year
For the preservation of your microwave and the health of your family, here are 13 things (in addition to metal) that should never be placed in the microwave.
Styrofoam Cups and Containers
While polystyrene foam or Styrofoam containers do a good job in protecting foods in the refrigerator, they aren't made for the microwave. Transfer the food to a microwave-safe container before heating.
Paper Bags and Takeout Containers
Unless the paper bag is developed for use in the microwave, like popcorn bags, it is not safe to use for reheating. Brown paper lunch bags and printed paper takeout containers can release toxins into foods and can easily catch fire if the food becomes too hot. And don't forget that those paper Chinese food containers often have a thin metal wire handle that can create sparks and flames to ruin your microwave.
Lightweight Plastic Bags and Containers
Keep grocery bags and any other lightweight plastic bags out of the microwave. They will melt! The same rule should be followed for margarine, yogurt, and cottage cheese tubs that are meant only for cold storage and one-time use. It may seem earth-friendly to reuse them, but it's not worth the risk of the chemicals released into your food during heating or a fire caused by the container melting.
Many plastic containers contain bisphenol A or BPA, a chemical that has been linked to numerous health issues from cancer to diabetes. Heating the plastic releases the BPA into the food. Take the time to check that any plastic storage container is labeled as microwave-safe before hitting those buttons.
If your coffee needs to be warmed up, use a glass or porcelain mug to heat it in the microwave before you pour it into a travel mug. Most mugs, cups, and bottles are made of plastic or stainless steel. You know that metal is a no-no for the microwave, and it will prevent the beverage from being heated. Plastic mugs may not be safe and can even separate and ruin the insulation that keeps the beverage hot.
Vintage Plates and Cups
If you have some vintage Fiestaware or any dish-ware that is more than 40 years old, don't use them in the microwave. The glaze could contain lead or other components that could leach into food when heated to high temperatures. Any gold or silver-gilded dishes should also be avoided.
Unless you like cleaning the microwave, make sure that every container is covered. A vented microwave cover will make your life much easier.
Fabrics and Clothes
This may seem out of place, but there are "hacks" floating around the internet that you can dry fabrics in the microwave. Never put any type of linens or clothing in the microwave. Your damp shoes will never be the same.
Whether there is the potential for explosion, eye-burning fumes, or unsafe temperatures, there are some foods that should not be prepared in the microwave.
- Hot Peppers: Unless you like the effects of pepper spray, avoid placing chili peppers in the microwave. The heat releases the capsaicin in the peppers and causes it to vaporize, burning your eyes, nose, and lungs.
- Eggs in the Shell: As the egg heats, all that steam has nowhere to go in the shell until it builds to the point where the egg explodes—even if you place it in a dish with water.
- Whole Fruits: Placing grapes, whole peaches, apples, or pears in a microwave can cause an explosion when the steam builds up inside the skin or create a serious burn when you try to open the steaming hot fruit.
- Frozen Meats: One of the benefits of the microwave is the quick, intense heat to thaw and cook frozen foods. One of the foods that should be monitored carefully is frozen meat. Because the meat is usually thick—especially ground beef—it is difficult to ensure that the center is fully-cooked. This can result in over-cooked areas while some spots are still raw.
- Frozen Breast Milk: Breast milk should be thawed in the refrigerator instead of the microwave. Uneven heating is dangerous and can burn the baby's throat.
Nothing at All
Finally, never turn on the microwave when it is empty. When the microwaves have no destination like liquids or food, they bounce off each other and are reabsorbed into the microwave, which can cause it to explode and start a potentially deadly fire.
Cooking Fires Public Education. National Fire Protection Association.
Home Cooking Fires, News & Research. National Fire Protection Association.
Kitchen Safety: Some Recycled Containers Are Not Food Safe. University of Illinois College of Agriculture, Consumer & Environmental Sciences.
Provvisiero DP, Pivonello C, Muscogiuri G, et al. Influence of Bisphenol A on Type 2 Diabetes Mellitus. Int J Environ Res Public Health. 2016;13(10):989. doi:10.3390/ijerph13100989
Heating Human Milk. La Leche League International.