A friend of mine posted a link on Facebook to a Change.org petition to stop using styrofoam cups at Dunkin Donuts. Amongst their complaints was that styrofoam cups caused health issues for the staff and customers:
The effects are usually irritated skin, eyes, stomach effects, and common cold. If a worker is constantly having contact with Styrofoam, it can cause hopelessness, headaches, sleepiness, weakness, or effects on the kidney. Another shocking reason is that, drinks held in Styrofoam cups soak up a bit of something from the Styrofoam. Scientists found this out by weighing a brand new cup, then weighing the same cup after someone drank out of it. The cup was lighter!
The Wikipedia page for styrofoam warns that styrene is possibly carcinogenic.
However, the US Food and Drug Administraion (FDA) claim:
Polystyrene and rubber-modified polystyrene identified in this section may be safely used as components of articles intended for use in contact with food, subject to the provisions of this section.
Are styrofoam cups safe for handling and drinking from?