Recently, there was a widely forwarded email warning regarding the dangers of microwaving food in plastic due to risk of cancer. I followed up with snopes.com and found out the following information, released officially from Johns Hopkins University:

The email that circulated claimed that dioxins found in plastic containers are released when heated, causing them to seep into food and water. Dioxins are highly cancerous and are considered possibly the most dangerous to mankind. They include chlorinated molecules of dibenzo-p-dioxin and chlorinated dibenzofurans. Some polychlorinated biphenyls (PCBs) are considered as dioxin-like compounds. They are produced inadvertently during the bleaching of pulp and manufacturing of pesticides. That's the bad news.

The good news is that there are no dioxins in plastics. There are compounds called phthalates that are sometimes added to plastics to make them flexible and less brittle. Phthalates are environmental contaminants that can exhibit hormone-like behavior by acting as endocrine disruptors. If you heat up plastics, you could increase the leaching of phthalates from the containers into water and food.

And yes, heating food in plastics does cause ingredients of the plastic to seep into the food. Have you ever noticed that packages for some straws or beverage cups are labelled "Not For Hot Drinks"? The heat will definitely extract chemicals from the plastic. It is best to heat food in inert containers, such as glass, ceramic or pyrex.

Don't worry about freezing things in plastic; cold temperatures do not facillitate the release of chemicals.

For more information visit www.snopes.com.