Aluminum foil is an all-purpose kitchen product with nearly countless uses. Folded into a decorative swan, it keeps restaurant leftovers safe. It ensures that tender vegetables are protected from burning on the grill or the campfire. And it makes cleanup a breeze when roasting dinner on a sheet pan.

While there are many great ways to use aluminum foil in the kitchen, it could actually create challenges—particularly when airflow is critical—and could even be a food safety concern if used improperly.

“Aluminum foil is one of the most widely used items in American kitchens. It’s convenient, versatile and easy to grab when you’re cooking, baking or storing leftovers,” said Dr. Darin Detwiler, a professor at Northeastern University’s College of Professional Studies and a food safety advocate and educator. “But there are certain situations where using foil can actually pose risks to your health and food safety.”

While aluminum foil is convenient and easy to use, there are several situations where it’s not the right tool for the job. Here are some ways you should never use aluminum foil because of food safety concerns, general safety or even culinary quality.

1. Avoid Using Foil with Acidic Foods

Acidic foods—like tomatoes, vinegar or citrus—can corrode or discolor aluminum. That means if you are marinating chicken breasts in lemon juice and oil, use a glass or ceramic storage container instead of aluminum foil. According to Detwiler, acidic ingredients can cause a chemical reaction that could not only produce a metallic taste but also release aluminum into the food. There is actually a fairly high likelihood of this reaction occurring, and the health risks could lead to gastric irritation or long-term neurological concerns, Detwiler explains.

2. Don’t Store Leftovers in Foil Long-Term

While wrapping room-temperature leftovers (like steamed ears of corn) in foil is generally safe, you should not use aluminum for longer-term storage. “Aluminum foil is not airtight,” Detwiler says. “Wrapping leftovers in foil allows air and bacteria to enter, which increases the risk of spoilage and foodborne illness.” Of course, if the food is acidic, you also run the risk of aluminum leaching into the food over time. Instead, use an airtight glass or ceramic container for longer-term storage. 

3. Skip the Foil When Baking

Aluminum is a high conductor of heat, so if you use an aluminum foil–lined baking sheet to make cookies or other baked goods, there’s a good chance the bottoms will brown or even burn. If you use regular gauge foil, it could also tear easily and lead to sticking. If your baked goods happen to be acidic, like lemon drop cookies, they could taste metallic. Instead, opt for a reusable silicone baking mat or parchment paper for more even heat distribution.

4. Never Microwave Foil

You should never put metal in a microwave, as it could produce sparks or fires. Since aluminum foil is metal, avoid wrapping your russet potatoes in aluminum foil (as you might when baking them) before microwaving them—just use paper towels instead. When covering plates or bowls, reach for parchment paper or microwave-safe covers to prevent splatters or spills. 

5. Avoid Using Foil at Very High Temperatures

One of the biggest selling points of aluminum foil is that it can withstand high temperatures. However, cooking at a very high temperature for too long, whether in the oven or on the grill, can lead to the foil breaking down, especially when it’s in direct contact with food or exposed to open flame. Detwiler explaines, “This can cause aluminum to migrate into your food, a process where small amounts of the metal dissolve into what you’re eating.” 

Reynolds Wrap actually makes foil for the grill, which is heavier-duty than its everyday foil. The company says, “Reynolds Wrap Grill Foil is designed to take the high heat of the grill as well as the low temperatures of the freezer. It is safe at any temperature ranging from -40° F to 650° F.”

The potential for the foil to degrade or break down occurs more frequently above 400° F and when the foil itself comes into contact with foods that are acidic or especially salty, says Detwiler. “Although occasional use may not cause harm in healthy individuals, repeated exposure can lead to a gradual buildup of aluminum in the body, especially for people with reduced kidney function,” he adds. 

6. Don’t Line an Oven or Grill with Foil

While not a food safety concern, lining the bottom of a grill or oven with a layer of aluminum foil can be a big problem. The foil may not stand up to the high heat, and it could actually scratch your oven. In addition, it could damage heating elements or interfere with the open flames of a gas oven. 

A layer of foil on the bottom of the oven could block airflow and make for very uneven heating. Grease could build up on the foil and ignite a fire. These same concerns are true for a grill; airflow is critical for grilling, so it’s best to save the foil for quick-cooking grilled vegetable packets.

The Bottom Line

There is no doubt that aluminum foil is convenient, but it was never meant to be the Swiss Army knife of kitchen tools, according to Detwiler. There are a number of everyday uses that “carry hidden risks that can add up over time,” he said. “By understanding where those risks lie and choosing safer alternatives, home cooks can protect their health and food quality without sacrificing convenience.”

Aluminum is not just found in foil; it’s also in some baking powders and medications. Small amounts are typically excreted by the body, but overexposure could pose health risks—especially in those with kidney problems, warned Detwiler. In almost all cases, opting for glass containers, parchment paper or silicone mats may be a healthier and safer choice.

One final note: Aluminum foil is recyclable, and in some circumstances it’s reusable. However, do not reuse it if it comes in contact with raw meat or seafood, as it could carry foodborne diseases. When you are ready to dispose of it, clean it well, ball it up, and find a local recycle program that accepts aluminum foil.