Data shows girls worldwide are entering puberty younger than ever. While the average age for the first period was 16 or 17 in the 1840s, it is now around 12. Breast development often starts as early as 9 or 10 today.
References:
Willyard, C. (2026). Why are girls starting puberty so young? Nature, 649, 816-818.Marshall, W. A., & Tanner, J. M. (1969). Variations in pattern of pubertal changes in girls. Archives of Disease in Childhood, 44(235), 291-303.Herman-Giddens, M. E., et al. (1997). Secondary sexual characteristics and menses in young girls seen in office practice: A study from the Pediatric Research in Office Settings network. Pediatrics, 99(4), 505-512.Aksglaede, L., et al. (2009). Recent decline in age at breast development: The Copenhagen Puberty Study. Pediatrics, 123(5), e932-e939.Eckert-Lind, C., et al. (2020). Worldwide secular trends in age at pubertal onset assessed by breast development among girls: A systematic review and meta-analysis. JAMA Pediatrics, 174(4), e195881.
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