Non-Microwave Safe Plastics

• According to the U.S. Department of Agriculture's Food Safety and Inspection Service, "plastic storage containers such as margarine tubs, take-out containers, whipped topping bowls, and other one-time use containers should not be used in microwave ovens." Additionally, the USDA advises not to use plastic storage bags and plastic grocery bags in the microwave or let plastic wrap touch foods during microwaving. These containers and plastic can warp or melt if used in the microwave and release harmful chemicals.
  
  

Non-Microwave Safe Plastics' Dangers

• Harmful chemicals in plastic, particularly bisphenol A, are most likely to migrate into food when exposed to high heat, according to the Preventive Medicine website. These chemicals may be carcinogenic, hormone-altering or cause allergic reactions. Additionally, studies have shown that bisphenol A has affected mice by causing chromosomal abnormalities, hormonal imbalances, spontaneous abortions, decreased sperm counts, impaired reproductive organs and changes in tissue that resemble early-stage breast cancer. The Food and Drug Administration and the National Toxicology Program agree that recent studies provide reason for some concern about the potential effects of bisphenol A "on the brain, behavior, and prostate gland of fetuses, infants and children."
  
  

Microwave-Safe Plastics

• The FDA requires that plastic manufacturers test containers for microwave approval and only containers that pass the test can display a "microwave-safe" icon, meaning that it is found safe for that purpose. However, according to the Harvard Medical School Family Health Guide, plastic containers that are not marked aren't necessarily unsafe, but rather, have not been determined by the FDA to be safe because it was not tested for use in the microwave.
  
  

Microwave Safety

• Recycling symbols on plastic, which indicate the type of plastic, are useful for determining which plastics to avoid in the microwave. Type 5 plastics are most commonly labeled "microwave safe." However, the best way to determine if plastic is microwave safe is if the plastic indicates that it is. If in doubt, use a glass or ceramic container instead. The USDA Food Safety and Inspection Service advises to "only use cookware that is specially manufactured for use in the microwave oven," and to never use brown paper bags, newspapers or aluminum foil in the microwave. Always follow instructions on containers for proper microwave use.