Over time, the chemical bond connecting the BPA building blocks deteriorates, releasing BPA molecules. The quantity released is typically very low, but the plastics are so widespread—they're in baby bottles, water bottles, metal food cans, food storage containers—that people are regularly exposed. In a 2003-2004 study by the U.S. Centers for Disease Control, nearly 93 percent of the people tested, age six and above, had detectable bisphenol A in their urine; females had slightly higher levels than males.