- The urban legend research site Snopes.com traces the origins of the scare over microwaving and freezing plastics to a brief health spot aired on a Hawaii news broadcast in 2002. In this broadcast, a medical director claimed that combining heat with high-fat foods can draw out dioxins, highly toxic chemicals that can cause cancer, liver damage, reproductive problems and skin disorders. In 2004, the claim expanded to include freezing water in plastic bottles, another practice said to release carcinogenic dioxins.
- When materials are heated, they can release chemicals from the material. These products can leach into food and pose a health hazard. However, Rolf Halden, Ph.D., of the Johns Hopkins Bloomberg School of Public Health points out that plastics do not contain dioxins. The American Chemistry Council adds that the temperature required to extract dioxins even if they were present -- 700 degrees F -- isn't reached in a microwave.
Microwaves can pose health risks, however, if you use them to reheat food in plastic containers or wrappers not intended for use in the microwave. Plastics can melt under high heat and contaminate the food. - When using a microwave to cook or reheat food, always use only containers and wraps marked as safe for use in the microwave. These products are specially formulated to withstand high heat without breaking down and releasing chemicals into the food. Contrary to popular belief, recycling symbols do not communicate a plastic's microwave safety. Containers such as butter or yogurt containers, designed for cold storage, can melt and should never be used in the microwave. Even when using a microwave-safe plastic wrap, do not allow it to come in contact with the food, as the high heat of the food can cause the wrap to melt.
- Although you should use caution when microwaving plastics, the same isn't true of freezing plastic bottles. According to Halden, in addition to beverage bottles containing no dioxins, the process of freezing the plastic makes it less likely that harmful chemicals will leach into your beverage. The Johns Hopkins Bloomberg School of Public Health, often cited as the source of the plastic bottle scare, states unequivocally on their website, "Freezing water does not cause the release of chemicals from plastic bottles."
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