Bisphenol A is a building block to several polymers and polymer additives. Bisphenol A has become controversial because it is an endocrine disruptor which mimics estrogen and therefore could induce hormonal responses.
Bisphenol A has been known to leach from the plastic lining of canned foods as well as polycarbonate plastics. Studies by the CDC found bisphenol A in the urine of 95% of adults sampled in 1988-1994 and in 93% of children and adults tested in 2003-04. Almost all exposure is through diet, and infants fed with liquid formula are among the most exposed.
There are seven classes of plastics used in packaging applications. Type 7 is the catch-all "other" class, some of which are made from bisphenol A monomer. When these plastics are exposed to hot liquids, bisphenol A leaches out 55 times faster than it does under normal conditions, at up to 32 ng/hour. Type 3 (PVC) can also contain bisphenol A. Types 1 (PET), 2 (HDPE), 4 (LDPE), 5 (polypropylene), and 6 (polystyrene) do not use bisphenol A during polymerization or package forming, and will not leach bisphenol A into food or beverages.