Home Improvement Skills & Specialties Electrical Appliances

15 Things You Should Never Put in the Microwave, From Styrofoam to Travel Mugs

Here's what isn't safe to heat up in the microwave, and why.

Plastic container and microwave

 BRETT STEVENS/ Cultura/ Getty Images

How many of us have wondered, "Can you microwave Styrofoam cups and containers?" Most of us learned to keep items such as aluminum foil and metal utensils out of this appliance when we saw the sparks but there are plenty of other items to keep out of the microwave, as well. For the preservation of your microwave and more importantly the health of your family, here are 15 things (in addition to metal that can't go in the microwave) that should never be placed in the microwave.

  • 01 of 15

    Styrofoam Cups and Containers

    Styrofoam containers piled up.

    Supersmario / Getty Images

    While polystyrene foam or Styrofoam containers do a good job of protecting foods in the refrigerator, most foam containers are not made for the microwave. Microwaving this type of foam can cause the carcinogenic substance styrene to seep into your food. The high heat can cause the container to break, dispersing hot food that can cause burns and acrid smells. Transfer the food to a microwave-safe container before heating.

  • 02 of 15

    Paper Bags and Takeout Containers

    Supply of cardboard takeout containers.

    olga_prava / Getty Images

    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. If you're confused or questioning whether the container you have is microwave-safe, don't put it in the microwave.

  • 03 of 15

    Lightweight Plastic Bags and Containers

    Plastic food containers
    Store leftover beans tightly covered in the fridge. photo (c) jmalov / Getty Images

    Keep grocery bags and any other lightweight plastic bags out of the microwave because they can 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.

  • 04 of 15

    Travel Mugs

    simply-recipes-best-travel-coffee-mugs

    Getty Images

    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 travel 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.

    Continue to 5 of 15 below
  • 05 of 15

    Vintage Plates and Cups

    Vintage plates with silver teaspoons
    segray / Getty Images

    If you have some vintage Fiestaware or any dishware 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.

  • 06 of 15

    Uncovered Containers

    A plastic no-splatter lid sits atop a bowl of heated soup inside of a microwave.

    The Spruce / Allison Wignall

    Unless you like cleaning the microwave, make sure that every container is covered. A vented microwave cover will make your life much easier. For example, if you put any type of container with any type of sauce (such as tomato) in the microwave without a cover, you can be sure the contents will explode in the microwave from becoming rapidly overheated.

  • 07 of 15

    Fabrics and Clothes

    Reading clothing care labels before washing

    The Spruce / Sarah Lee

    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—let them safely air dry.

  • 08 of 15

    Hot Peppers

    hot peppers at various stages of ripening

    The Spruce / Adrienne Legault  

    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.

    Continue to 9 of 15 below
  • 09 of 15

    Egg in a Shell

    Egg Carton
    Egg Carton

    Justin Sullivan / Getty Images

    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. If you're making an egg in a mug recipe, you've hopefully cracked the egg out of its shell and beat it a bit, so it's safer to microwave without making much of a mess or explosion.

  • 10 of 15

    Whole Fruits

    how-to-store-grapes-GettyImages-1159851222

    Larisa Davydova / Getty Images

    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 scald when you try to open the steaming hot fruit.

  • 11 of 15

    Frozen Meats

    frozen meat on white dish

    nataliaspb / Getty Images

    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.

  • 12 of 15

    Frozen Breast Milk

    Bags of frozen breast milk

    Cara Dolan / Stocksy

    Breast milk should be thawed in the refrigerator instead of the microwave. Uneven heating is dangerous and can scald the baby's throat.

    Continue to 13 of 15 below
  • 13 of 15

    Nothing at All

    open microwave

    Basak Gurbuz Derman / Getty Images

    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.

  • 14 of 15

    Leafy Greens

    A bowl of raw spinach beside a bowl of raw kale

    Anthony Boulton / Getty Images

    Leafy greens such as kale, raw carrots, and fresh spinach, and sometimes processed meats such as hot dogs, can cause sparking and arcing in the microwave while cooking. The likely reason is metallic trace minerals in the food are reacting to the microwaves. The food may not heat up evenly, but more importantly, arcing can damage your microwave oven. If you see arcing (sparking), stop the oven, and remove the item immediately to avoid damage to your microwave.

  • 15 of 15

    Cup of Water

    ceramic mug in microwave

    miguelangelortega / Getty Images

    Boiling a cup of water in the microwave seems quick and easy. But, if you overdo it, the cup and the water can be extremely hot, causing scalding and minor burns, or it could explode (rare) while in the microwave. Though it can take a minute or so longer, it's safest to boil water the old-fashioned way in a pot or kettle on the stove.

    Warning

    Can you put glass in the microwave? To be on the safe side, only put glass in your microwave if it is labeled as "microwavable safe." If it has that label, it is designed to withstand the high temperatures of a microwave oven. Other types of glass may shatter if microwaved.

The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Styrene. United States Department of Health and Human Services.

  2. Use only microwave safe containers when cooking and reheating foods. Michigan State University.

  3. Pérez-Bermejo M, Mas-Pérez I, Murillo-Llorente MT. The Role of the Bisphenol A in Diabetes and Obesity. Biomedicines. 2021 Jun 10;9(6):666. doi: 10.3390/biomedicines9060666. PMID: 34200822; PMCID: PMC8230545.

  4. Lead Contamination of Food. Extonet, Oregon State University.

  5. Fattori V, Hohmann MS, Rossaneis AC, Pinho-Ribeiro FA, Verri WA. Capsaicin: Current Understanding of Its Mechanisms and Therapy of Pain and Other Pre-Clinical and Clinical Uses. Molecules. 2016 Jun 28;21(7):844. doi: 10.3390/molecules21070844. PMID: 27367653; PMCID: PMC6273101.

  6. Heating Human Milk. La Leche League International.

  7. Cooking With Microwave Ovens: What is Arcing? USDA Food Safety and Inspection Service.

  8. Risk of Burns from Eruptions of Hot Water Overheated in Microwave Ovens. U.S. Food and Drug Administration.