Age of first menarche has long been seen as a girl's start to puberty, but breast development may be a better fit.
It’s no secret that girls are entering puberty earlier and earlier, but a new study suggests that it’s happening as rapidly as 3 months earlier with each decade of women.1
How the onset of puberty for women is gauged can be debated, with many studies focusing on a woman’s recall of her age at her first period (menarche) as a benchmark. New literature, however, turns the focus to breast development as the most reliable tool for measuring progress through puberty in girls.
Katherine Kutney, MD, a pediatric endocrinologist at Rainbow Babies and Children’s Hospital in Cleveland, Ohio, said that, like in boys, physical indicators are a better way to diagnose the onset of puberty in the clinical setting.
For both boys and girls, the puberty process is triggered by the activation of the hypothalamic-pituitary-gonadal (HPG) axis. For boys, this causes testicular growth, which is the first clinical sign that a male has entered central puberty. For girls, although first menstruation might traditionally have been considered to be a sign that puberty has begun, it actually begins with thelarche, or breast development.
Tanner staging, also known as the Sexual Maturity Rating (SMR) scale, is the standard system for measuring progress through puberty, Kutney said. For boys, this scale assigns stages to signify progress through puberty based on pubic hair and genitalia development. For girls, the scale uses measurements of breast tissue and public hair development.
Pubic hair development, a process called adrenarche, can occur at the same time as thelarche, but it doesn’t always. This process, which is triggered with the release of female sex hormones, spurs the growth of pubic and axillary hair, the development of adult body odors, and acne.
Tanner Staging for Females2
Breast development scale
Earlier onset of puberty in girls has been noted for some time, but the 2020 study suggests that it has progressed to such a point that guidelines may need to be adjusted to redefine precocious, or “early,” puberty designations. Kutney said the average onset of puberty for girls is around age 10 years, but it can occur in as young as 8 years of age for girls from African American and Hispanic ethnicities. The upper age limit for puberty onset in girls is age 12 years, she added.
1. Eckert-Lind C, Busch AS, Petersen JH, et al. Worldwide secular trends in age at pubertal onset assessed by breast development among girls: a systematic review and meta-analysis. JAMA Pediatr. 2020;174(4):e195881. doi:10.1001/jamapediatrics.2019.5881
2. Emmanuel M, Bokor BR. Tanner stages. StatPearls Publishing. 2021.