The convenience of microwaving food in plastic containers is a common practice, but this habit requires careful attention to safety. When a plastic container is labeled “microwave safe,” it means the material has been tested and certified by regulatory bodies like the Food and Drug Administration (FDA) to withstand microwave energy without melting, warping, or degrading under normal use. Choosing the correct container is not simply a matter of preventing a mess; it is a fundamental health and safety concern for consumers. Using a container not intended for heating can lead to the release of chemical additives from the plastic directly into the food.
Decoding Microwave-Safe Labels and Symbols
Consumers have a straightforward way to determine a container’s suitability by examining the manufacturer’s labeling. The most reliable indicator is a specific symbol found on the bottom or side of the plastic item. This icon typically features a microwave oven graphic or a set of three wavy lines, which represent the microwave energy. If this symbol is present, the manufacturer has designed and tested the product for microwave use.
The plastic Resin Identification Codes (RICs), the numbers 1 through 7 inside a chasing-arrows triangle, identify the plastic polymer type primarily for recycling purposes. While these codes are helpful for sorting, they do not automatically guarantee a container is safe for heating. Therefore, the microwave-safe icon should always be considered the definitive confirmation, regardless of the RIC number.
The Chemical Risks of Heating Unsafe Plastics
When plastics not specifically formulated for heat are exposed to microwave energy, the primary risk involves the migration of chemical additives into the food. The heat causes the polymer chains within the plastic structure to break down and become less stable. This destabilization increases the rate at which various non-polymerized chemical components, such as plasticizers and stabilizers, can leach out.
Two of the most well-known substances of concern are Bisphenol A (BPA) and phthalates. BPA is often used to make hard, clear plastics, while phthalates are added to make plastics more flexible and durable. Both BPA and phthalates are known as endocrine-disrupting chemicals. These endocrine disruptors can interfere with the body’s hormonal systems, which regulate processes such as development, metabolism, and reproduction. The risk of chemical migration is significantly higher when plastic is heated, as elevated temperatures accelerate the breakdown and release of these chemicals.
Specific Resin Codes and Their Microwave Suitability
The Resin Identification Codes (RICs) offer general guidance on a plastic’s material composition, with some types being inherently more heat-tolerant than others. Polypropylene, identified by the number 5 (PP), is generally considered the most suitable plastic for microwave containers. This material has a high melting point, often able to withstand temperatures up to approximately 230°F (110°C), making it resistant to deformation during typical reheating.
High-Density Polyethylene, code number 2 (HDPE), is sometimes used in microwave-safe products, but consumers should still verify the presence of the microwave icon. Other plastic types should be avoided unless they are a specialized, explicitly labeled variant. For instance, Polyethylene Terephthalate, code number 1 (PET), used in many clear beverage bottles, is not microwave-safe and may melt. However, one variation, Crystalline PET (CPET), is opaque and engineered for high-temperature applications, often found in pre-packaged microwavable meal trays. Polystyrene, code number 6 (PS), commonly found in foam cups and takeout containers, and Polyvinyl Chloride, code number 3 (PVC), should not be microwaved, as they can easily melt and leach chemicals. Plastics marked with code number 7, categorized as “Other,” are a mix of resins and should be avoided unless they carry the official microwave-safe symbol.
Practical Guidelines for Safe Microwaving of Plastics
Even when using plastic containers labeled as microwave-safe, certain practices are necessary to maintain safety and container integrity. Foods high in fat or sugar, such as oils, meats, and sauces, can reach temperatures significantly higher than the boiling point of water. These extreme temperatures can exceed the plastic’s tolerance, potentially causing the material to warp or melt, which increases the possibility of chemical migration.
It is important to ensure that the container is vented by either removing the lid or lifting one edge before heating. This allows steam to escape, preventing pressure buildup that could damage the container or cause the contents to splatter. Additionally, consumers should avoid microwaving plastic containers that show signs of wear, such as cloudiness, scratches, or deep stains. Degradation from repeated use, washing, or abrasion can compromise the plastic’s surface and increase the potential for chemical release. If using plastic wrap, only use products specifically labeled for microwave use, and ensure the film does not touch the food. Furthermore, single-use plastics, like yogurt tubs or margarine containers, are generally not designed to withstand repeated heating cycles and should not be reused for microwaving.