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Around this time, the University of Missouri’s vom Saal, a garrulous biologist who previously worked as a bush pilot in Kenya, began studying the effects of synthetic estrogens on fetal mouse development. The first substance he tested was BPA, a chemical used in clear, hard plastics, particularly the variety known as polycarbonate, to make them more flexible and durable. (It’s also found in everyday items, from dental sealants and hospital blood bags to cash register receipts and the lining of tin cans.) Naturally occurring estrogens bind with proteins in the blood, limiting the amount that reaches estrogen receptors. But vom Saal found this wasn’t true of BPA, which bypassed the body’s natural barrier system and burrowed deep into the cells of laboratory mice.
Puberty is considered precocious ( precocious puberty ) if secondary sex characteristics occur before the age of 8 in girls and 9 years in boys.   Increased growth is often the first change in precocious puberty, followed by breast development and growth of pubic hair. However, thelarche , adrenarche , and linear growth [ clarification needed ] can occur simultaneously and although uncommon, menarche can be the first sign.  Precocious puberty can be classified into central (gonadotropin-dependent) precocious puberty or peripheral (gonadotropin-independent) puberty.   Peripheral precocious puberty has been linked to exposure to exogenous estrogenic compounds.