Is It Safe to Reheat Food in Plastic?

Storing your leftovers in plastic containers and popping them into the microwave the next day probably feels like second nature. It’s convenient and quick – a routine many Americans rely on. 

But have you ever wondered about the safety of this habit? As practical as plastic containers are, heating them may come with hidden risks. What exactly are these plastics made of, and what happens when they’re heated again and again? This blog discusses these pressing questions and provides safer alternatives to use at home.

We speak to Shripal Bhavsar, M.D., an oncologist at INTEGRIS Health Cancer Institute, to learn more. 

“Research has found that chemicals in certain plastics can leach into food when exposed to heat, raising concerns about long-term health,” Bhavsar says. “To reduce these risks, consider reheating food in safer alternatives like glass or ceramic containers.”

What are plastic containers made of?

Key points: Plastic containers are primarily made from polymers, which are long chains of molecules derived from petroleum or natural gas. To improve their strength, flexibility and durability, manufacturers often add chemicals like plasticizers, stabilizers and colorants to the base material.

Plastics are made from organic polymers, which are large molecules consisting of repeating subunits called monomers. 

• These monomers, often derived from petroleum or natural gas, are chemically bonded together to create a durable and versatile material.
• Plastics also contain various additives like plasticizers, stabilizers and colorants to enhance flexibility, durability and appearance.
• Common additives include bisphenol A (BPA) and phthalates, which are used to make plastics stronger or more flexible.

BPA is an industrial chemical used primarily to create clear, rigid plastics, such as polycarbonate plastics.

• Its main role is to improve the strength and longevity of plastic products. 

Phthalates are a group of chemicals added to plastics, particularly polyvinyl chloride (PVC), to increase flexibility, softness and elasticity. 

• You’ll often find phthalates in plastic wraps and food storage containers.

What happens when plastic is heated?

What to know: When you reheat food in plastic containers, there’s a risk of chemicals migrating from the plastic into your food, particularly when the plastic is exposed to high temperatures. 

The process of leaching occurs because heat weakens the chemical bonds of polymers and increases the mobility of additives within the material, allowing chemicals to break down and escape into food or liquids. 

• Repeated use, wear and tear, and high temperatures intensify this risk.
• Plastics labeled with recycling codes 3 (PVC), 6 (polystyrene) and 7 (a category that includes BPA-containing plastics) are more likely to release harmful substances under heat stress.
• By contrast, plastics labeled as BPA-free or made of inert materials like polyethylene or polypropylene are generally considered safer.

The danger arises when these chemicals migrate from the packaging due to heat, wear and tear and the contents of the food.

• High temperatures, such as those from microwaving or storing hot food in plastic containers, weaken the polymer structure of plastics.
• Old, scratched or damaged plastics are even more likely to leach chemicals, as the protective structure is degraded.
• Foods high in fat or acidic content are known to absorb these chemicals more readily when they come into contact with plastic packaging.

The temperature at which plastics begin to leach chemicals into food or liquids can vary depending on the type of plastic, its chemical composition, the food being heated and the condition of the plastic. 

• While there’s no “universal” temperature for all plastics, research indicates that chemical leaching typically occurs at temperatures above 100 F and increases progressively as the temperature rises.
• Mild heating (100 to 120 F) can result in low levels of leaching.
• Hotter temperatures used for boiling, microwaving or storing hot food (above 160 F) significantly increase the risk.
• Extended exposure to direct heat, such as in ovens or boiling liquids (212 F and above), poses the highest danger of chemical leaching.

What are the risks of plastics entering the body?

Why it matters: Chemicals in plastics act as endocrine disruptors, interfering with hormonal balance, which can lead to reproductive issues, including infertility and developmental problems in children. Prolonged exposure has also been linked to chronic inflammation, weakened immune response and increased risks of cancer, obesity and cardiovascular conditions. The risks are amplified by high temperatures, fatty or acidic foods and damaged or lower-quality plastics.

Hormonal disruption occurs when plastics interfere with the body’s natural balance.

• BPA imitates estrogen, leading to potential overproduction or suppression of normal hormone functions.
• Phthalates can suppress testosterone production, disrupting male reproductive health and fetal development during pregnancy.
• Long-term exposure is associated with developmental disruptions in children, early puberty, thyroid dysfunction and disorders of the adrenal and reproductive systems.

Reproductive health risks are associated with exposure to chemicals from plastics, particularly BPA and phthalates.

• There is a connection between BPA exposure and reduced egg quality in women or lowered sperm count and motility in men.
• Chronic exposure has been associated with an increased risk of miscarriage, preterm birth and developmental issues in fetuses.
• Phthalates, which disrupt testosterone metabolism, can lead to congenital disorders in male infants, particularly conditions affecting the genitalia.

Immune system responses are heightened by the presence of plastics in the body.

• When plastics infiltrate organs or tissues, it can provoke low-level inflammation, which over time may contribute to autoimmune conditions.

Gastrointestinal and organ damage can occur when plastics enter the digestive tract and accumulate in tissues or organs.

• Persistent microplastic exposure may weaken the intestinal lining, allowing toxins and pathogens to enter the bloodstream.
• Plastics have been found in the liver, kidneys and lymphatic system after high exposure.

Certain chemicals associated with plastics have been linked to cancer development.

• Styrene (from polystyrene plastics) has been classified as a possible human carcinogen with links to disturbances in cellular DNA functions.
• Phthalates and BPA can cause oxidative stress and inflammatory pathways, increasing the risk of cancers like breast, prostate and liver cancer.

Metabolic and cardiovascular concerns have emerged as a growing concern.

• BPA has been linked to insulin resistance and disrupted fat cell regulation, both of which contribute to obesity and type 2 diabetes risk.
• Long-term BPA exposure is linked to higher risks of high blood pressure and cardiovascular disorders through its impact on estrogen pathways and metabolism.

What about microwave-safe containers?

Key points: Microwave-safe containers are typically made of polyethylene or polypropylene, which are more stable under heat. However, the “microwave-safe” label only means the container won’t melt – it doesn’t guarantee that leaching won’t occur. Even these safer plastics can release chemicals under prolonged or high heat conditions.

The "microwave-safe" label commonly found on containers indicates it won’t physically break down, release harmful fumes or lose its structural integrity when exposed to microwave heat. 

• That said, this certification doesn't account for whether the plastic might leach chemicals into food during reheating.
• It simply confirms that the material has been tested to handle microwave temperatures without obvious damage.

Chemicals in microwave-safe containers can eventually leach into food.

• Repeated exposure to high temperatures during microwaving can break down the plastics.
• Microwave-safe plastics are designed to withstand heat, but over time, wear and tear from repeated use, washing and heating can degrade the material.
• Fatty or acidic foods can interact more with the plastic, accelerating the release of chemicals into the food.

What to use instead

• Avoid plastic products marked with recycling codes 3 (PVC) and 7 (polycarbonate, often containing BPA).
• Look for labels that state “BPA-free” or “phthalate-free,” but note that alternative chemicals may still present some risks.
• Limit use of single-use plastics and prioritize fresh or minimally packaged foods.

For more health and wellness content, visit the INTEGRIS Health For You blog.

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