Hormones in milk will do that before make up. Earlier puberty is linked to cancer in sex organs (Breast, cervical, ovarian and womb). Women are meant to have very few menstrual cycles which should begin at 18 years and between pregnancies, a longer post-natal non reproductive period, alongside much longer breast feeding proffered a natural protection against these cancers. The desire for lots of babies, reduced or no breast feeding and girls having babies younger and younger means puberty is commencing at around 11 years..or even earlier. I read a really interesting paper on it once, women's bodies have evolved massively to meet societal requirements.