Scientists are n't sure what 's behind the increase in earlier puberty . Studies showed those who started smoking earlier at greater risk for certain diseases . Drugs : Chemicals such as bisphenol - A ( BPA ) may cause smoking .
Experts are n't sure what 's behind the increase in earlier puberty . Studies showed girls who started puberty earlier at greater risk for certain cancers . Doctor : Chemicals such as bisphenol-A ( BPA ) may affect hormones .