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The Danger of Reheating: Foods That Can Actually Become Toxic

Foods That Can Actually Become Toxic When Reheated

If you’re someone who cooks a lot, it’s hard not to end up with leftovers. You may be feeding other people in addition to yourself, or you may just be cooking for yourself. Either way, it’s hard to predict how much food will be eaten. Besides, leftovers don’t seem like the worst outcome-after all, it’s one less meal to cook in the future, right? Wrong, actually. Certain foods should never be kept as leftovers, let alone reheated for a second meal.
The reasons why certain foods become toxic when reheated can vary. It could be that the food was stored improperly and once reheated it becomes inedible. It could be that the food has been stored too long and is past its expiration date, or it could be that you’re not reheating the food to the correct temperature. Whatever the reason, the food is no longer safe and should not be eaten.
Reheating potentially toxic foods isn’t something to take lightly. Sure, there are some myths about microwaves that aren’t worth your time. But there have been cases of illness, death, and even amputation from leftover food poisoning. It’s not worth the risk of reheating those Tupperware containers just for the convenience of a free meal. Avoid disaster by reading on: these are foods that can actually become toxic when reheated.


Eating leftover rice can be dangerous. Bacillus cereus, a bacteria that causes food poisoning, is the main cause of concern. According to the National Health Service (NHS), Bacillus cereus spores can be present on rice from the start, even on uncooked grains. These spores can also remain on cooked rice. However, if cooked rice is left at room temperature for too long, these spores begin to grow into bacteria. This is when the real risk of food poisoning begins.
You want to avoid eating this toxic rice as much as possible. According to the BC Centre for Disease Control, symptoms of food poisoning caused by Bacillus cereus include vomiting, nausea, diarrhea and abdominal pain.
There are several steps you can take to avoid getting sick from leftover rice. First, let your cooked rice cool quickly, ideally within 1 hour of cooking. This limits the amount of time the rice is in the “danger zone,” between 40 and 140 degrees Fahrenheit, according to the U.S. Department of Agriculture’s (USDA) Food Safety and Inspection Service. You can store refrigerated rice for 3-4 days. During storage, your leftover rice may become hard and dry, slimy, or smelly. These are signs that your cooked rice has gone bad. When reheating, make sure your rice reaches 165 degrees Fahrenheit. This can be done either in the microwave or in a pan (via Real Simple). You need to follow these food safety steps from start to finish because, as the University of Florida explains, proper reheating isn’t always enough to kill Bacillus cereus.


There are risks to reheating chicken. Most people are familiar with the bacteria found in raw chicken, such as Salmonella, Clostridium perfringens, and Campylobacter (via the Centers for Disease Control and Prevention). However, these bacteria can remain on chicken if the meat is improperly cooked or reheated. As the San Francisco Gate explains, you can get food poisoning from salmonella if your chicken doesn’t reach the proper temperature when it’s reheated.
Reheated chicken can expose you to foodborne illnesses with serious consequences. Salmonella can cause death, but rarely does. People most likely to suffer death or other serious salmonella symptoms are those in vulnerable groups, such as the elderly, children, pregnant people, and people with weakened immune systems (via Healthline). More common, less serious salmonella symptoms include stomach pain, headache, chills, fever, diarrhea, or nausea.
Fortunately, you can avoid these side effects by taking precautions when reheating your chicken. After cooking chicken to the proper temperature (165 degrees Fahrenheit), you should put it away within 1 hour, just like cooked rice. Once stored in the refrigerator, cooked chicken will keep for 3-4 days (via USDA). When it’s time to reheat, you need to bring the entire chicken back up to 165 degrees Fahrenheit. Some people think this can’t happen when you reheat chicken in the microwave. Others, like Healthline, say the safest way is to reheat your leftovers the same way they were first cooked. Using a meat thermometer can eliminate the guessing game.


Like rice, potatoes are a starchy food that should be handled with care when reheating. Both rice and potatoes are carbohydrate-rich foods that contain the bacteria Bacillus cereus, which causes food poisoning. If not properly stored or heated to the correct temperature, the bacteria on potatoes can multiply and cause foodborne illness.
To ensure the safety of reheated potatoes, it is important to follow proper food handling and storage practices. After cooking, allow potatoes to cool quickly within 1 hour and store in the refrigerator. Properly stored, cooked potatoes will keep for 3-4 days. During storage, watch for signs of spoilage, such as a slimy texture or unpleasant odor.
When reheating potatoes, make sure they reach a temperature of at least 165 degrees Fahrenheit. This can be achieved by using a microwave or a stovetop pan. It is important to heat the entire portion of potatoes thoroughly to eliminate any bacteria that may be present.
Also, when reheating potatoes, avoid leaving them at room temperature for long periods of time. Bacteria can multiply rapidly in the “danger zone” between 40-140 degrees Fahrenheit. To prevent bacterial growth, it is best to reheat potatoes promptly and consume them immediately after reheating.


Eggs are a common ingredient in many dishes, but reheating them can be risky. The main concern with reheating eggs is the potential growth of bacteria, such as salmonella. Eggs can be contaminated with salmonella on the shell or even inside the egg. If eggs are not cooked or reheated properly, these bacteria can grow and cause foodborne illness.
To safely reheat eggs, make sure they are cooked thoroughly. The internal temperature of reheated eggs should reach 165 degrees Fahrenheit to kill any bacteria present. Avoid reheating eggs in their shells, as this can cause uneven heating and increase the risk of bacterial growth. Instead, consider cooking or reheating eggs in a separate dish, such as scrambled eggs or an omelet.
If you have leftover eggs, refrigerate them immediately and consume them within a few days. If you are unsure about the freshness or safety of eggs, it is better to throw them out rather than risk foodborne illness.


Spinach is a nutritious leafy green vegetable, but it can become toxic when reheated under certain conditions. The concern with reheating spinach is the potential for the growth of nitrites, which can convert to harmful nitrosamines. Nitrosamines are known carcinogens and may increase the risk of cancer.
To minimize the risk of nitrosamine formation, it is recommended that spinach be consumed immediately after cooking and not reheated. If you have leftover cooked spinach, it is best to store it in the refrigerator and consume it cold or at room temperature within a day or two.
If you must reheat spinach, do so at a low temperature and for a short time to minimize the formation of nitrosamines. However, it is still advisable to use caution and consume reheated spinach in moderation.

Fish & Seafood

Seafood, such as fish and shellfish, can be delicate and prone to bacterial contamination. Improper reheating of seafood can lead to the growth of bacteria such as Vibrio parahaemolyticus or Clostridium botulinum, which can cause food poisoning.
When reheating seafood, it is important to ensure that it reaches an internal temperature of at least 145 degrees Fahrenheit. This temperature is necessary to kill any bacteria or parasites that may be present. Using a food thermometer is the most reliable way to determine if seafood has been reheated to a safe temperature.
To prevent bacterial growth, it is important to handle seafood properly from the time of purchase. Store seafood in the refrigerator or freezer immediately and follow the recommended storage times. If seafood has been at room temperature for more than two hours, it is best to throw it away rather than risk foodborne illness.

Bottom line

While reheating leftovers can be convenient, it is important to be aware of the potential risks associated with certain foods. Rice, chicken, potatoes, eggs, spinach, and seafood are among the foods that can become toxic when improperly reheated. By following proper food handling, storage, and reheating practices, you can minimize the risk of foodborne illness and ensure the safety of your meals. Remember to chill leftovers quickly, store them in the refrigerator, and reheat them to the proper temperature before eating. Your health and well-being are worth the extra care and attention when reheating leftovers.


Reheating certain foods can cause bacteria to grow and toxins to form, increasing the risk of foodborne illness.

Why can rice become toxic when reheated?

Rice can become toxic when reheated due to the presence of Bacillus cereus bacteria. If cooked rice is left at room temperature for too long, the bacteria can multiply and produce toxins that can cause food poisoning.

How do I safely reheat chicken?

To safely reheat chicken, make sure it reaches an internal temperature of at least 165 degrees Fahrenheit. Use a meat thermometer to check the temperature and avoid reheating in the microwave, as uneven heating can leave some parts undercooked.

Can I reheat eggs without risk of foodborne illness?

Yes, you can recook eggs, but it’s important to cook them thoroughly and make sure they reach an internal temperature of 165 degrees Fahrenheit. Avoid reheating eggs in the shell to prevent uneven heating and the risk of bacterial growth.

Why should I avoid reheating spinach?

Reheating spinach can lead to the formation of harmful nitrosamines, which are known to be carcinogenic. It’s best to consume cooked spinach immediately after cooking or store it in the refrigerator and consume it cold or at room temperature within a day or two.

How can I prevent the growth of bacteria when reheating seafood?

To prevent bacterial growth when reheating seafood, make sure it reaches an internal temperature of at least 145 degrees Fahrenheit. Handle and store seafood properly, and discard any seafood that has been at room temperature for more than two hours to avoid the risk of food poisoning.

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