Once styrene gets into your food or drink—and then into you—what does it do? Studies suggest that styrene mimics estrogen in the body and can therefore disrupt normal hormone functions, possibly contributing to thyroid problems, menstrual irregularities, and other hormone-related problems, as well as breast cancer and prostate cancer. The estrogenicity of styrene is thought to be comparable to that of Bisphenol A, another potent estrogen mimic from the world of plastics.
Long-term exposure to small quantities of styrene is also suspected of causing:
low platelet counts or hemoglobin values;
chromosomal and lymphatic abnormalities;
neurotoxic effects due to accumulation of styrene in the tissues of the brain, spinal cord, and peripheral nerves, resulting in fatigue, nervousness, difficulty sleeping, and other acute or chronic health problems associated with the nervous system.
Read the whole article here : http://www.grinningplanet.com/2005/11-01/styrofoam-cups-article.htm
And plastic is just as bad.