Do styrofoam cups cause health issues?

Question

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?

Answer 1

If you follow the IARC link in the Wikipedia article, you'll find this evaluation:

5.5 Evaluation

There is limited evidence in humans for the carcinogenicity of styrene.

There is limited evidence in experimental animals for the carcinogenicity of styrene.

Also, in the Wikipedia article itself, it states the styrene has been identified as a "possible human carcinogen" (emphasis mine).

My impression, having looked through the IARC report but not any of the studies it refers to, is that the data is rather inconclusive. For example, from the IARC report:

The numbers of cases were quite small in these studies, and most of the larger cohort studies have not yielded similar findings.

and

The increased risks for lymphatic and haematopoietic neoplasms observed in some of the studies are generally small, statistically unstable and often based on subgroup analyses. These findings are not very robust and the possibility that the observations are the results of chance, bias or confounding by other occupational exposures cannot be ruled out. [emphasis mine]

Given that there have been a number of studies related to the carcinogenicity of styrene but none have conclusively shown that it is carcinogenic, styrene is at worst only slightly carcinogenic. That means that at worst your risk of developing cancer will only go up with very heavy exposure to it, and even then your risk probably isn't going up very much.