These days, if you go out to buy baby bottles, sippy cups, and other plastic products you might read a label that says "BPA-Free". Bisphenol A (BPA) was a substance commonly found in plastic bottles until studies came out showing that BPA, which mimics estrogen, was linked to health problems like altered brain and organ development, increased risk of breast cancer, infertility, heart problems, ADHD, and many others. After this knowledge came to light there was a backlash against BPA, with bills banning BPA products, retailers pulling BPA products of shelves, and manufacturers shifting towards making BPA-free products, all to reduce the health risk that BPA posed.
In an article by Mariah Blake of Mother Jones, however, it seems that BPA-free products are actually more dangerous than BPA products. According to the article, a study done by George Bittner, a professor of neurobiology at the University of Austin, Texas showed that almost all plastic products released synthetic estrogen, and that some of the BPA-free products released synthetic estrogen compounds that were more potent than BPA. It seems that when companies switched to BPA-free options, they were not required to test the new products for toxic compounds or synthetic hormones. Under US law, chemicals are deemed safe unless they are proven otherwise. Because they did not need to test the compounds in the BPA-free products, companies released BPA free plastic products that were supposed to be safer but in reality, posed a more significant health risk.
Alternative materials that are also available for baby bottles or other drinking containers include glass and stainless steel.
For a KQED radio discussion between Mariah Blake and other scientists go here.