Styrofoam is made by a combination of air and polystyrene. The two are molded into cells and pressed together. The main component of styrofoam is the chemical styrene. Polystyrene itself is non-toxic to our bodies; but it can cause an inflammatory response when enclosed within us. Depolymerization can occur at higher temperatures; when this happens chain scission may occur and monomers can be released. Polymers, at low temperatures are highly preferred in most cases, but at higher temperatures you may approach the ceiling temperature.
The ceiling temperature is where polymerization and depolymerization are at equilibrium with each other. Styrofoam is not FDA-approved inherently but can be manufactured in such a way so that it is. Styrofoam with a high ceiling temperature is better used and much less dangerous. The average microwave cannot reach a temperature high enough to hit the ceiling temperature. The ceiling temperature of polystyrene is three hundred ninety-five degrees celsius. The polymer would already have began charring at this temperature; in other words, you would need to make the polystyrene very very hot in order to release such monomers.
Short term exposure to the chemical styrene can cause stomachaches or irritation/inflammation of your eyes and nose. If you are exposed to this chemical at high temperatures for a longer period of time you may experience headaches, fatigue, depression, hearing loss, nervous system disfunction, or other symptoms. The temperature at which styrofoam is dangerous to be around is much higher than the maximum temperature that a microwave can reach. Certain forms of polystyrene will react differently at different temperatures but I would say do not place styrofoam in a microwave just to be safe. Unless it is written that the styrofoam has been tested and is microwave safe, just use a different material to heat up your food.
Sources:
http://theboard.byu.edu/questions/213/
http://www.reddit.com/r/askscience/comments/1bjzxo/can_you_microwave_styrofoam_is_it_safe_to_eat/
I actually had a really long debate with myself yesterday about whether or not to keep my sandwich in the styrofoam box or not. I thought it was not a good idea because the box did not say microwave safe. Luckily, I was reasonable yesterday and put it on a plate instead. I never knew that it could cause a very dangerous chemical.
I have always been told to not put styrofoam in the microwave because it can cause cancer. I researched this topic and found that styrofoam is a type of plastic and it should not be used when microwaving food because some of the toxic ingredients in styrofoam can get into your food. I found an article from Harvard and it mentions that some styrofoam is okay to microwave, but it is important to read the label too see what it says about what is and is not safe. http://www.health.harvard.edu/healthbeat/HEALTHbeat_081606.htm
I always knew that putting styrofoam in the microwave could be dangerous, as well as certain types of plastic. Since coming to college though I learned that not everyone was taught this lesson. I wonder if there has been a study done on the long term affects of small amounts of styrofoam consumption and if it can lead to health problems further down the road. We know there is a connection between plastic and carcinogens but I wonder if the same will be found for this as well. I think a study done on this topic would be extremely beneficial especially since dumb college students are still heating up food on Styrofoam plates.