Bisphenol A (BPA) is a ubiquitous compound in plastic and is a key building block of the material. It is routinely used to line cans, to prevent corrosion and contamination. More than 2.3 billion pounds of it are manufactured in the U.S. annually.
The dangers of BPA are controversial; studies have shown that exposure to it promotes breast cancer cell growth (and other ill effects), but its use prevails because it is cheap, lightweight, durable and offers other hard-to-match features, and its adverse effects in humans are not yet proven. It has been found in more than 90 percent of human urine samples; we face low-level but very regular exposure to it, and those considered to be at highest risk are babies.
BPA leaches out of plastic 55 times faster when exposed to heat, so if used, it should never be microwaved, used to store hot liquids or foods, or washed in hot water (by hand or in dishwashers). (Source: Scientific American, Photo: Flickr)