Nuances of puberty, the actual trigger, influencing factors, secular and tempo changes, continue to plague us. Uncertainty, as in quantum physics, may continue. Niels Bohr concluded decades ago that what you see depends on how you look. In the robust Breast Cancer and the Environment Research Centers (BCERC) study in this issue of Pediatrics by Biro et al, onset of Tanner 2 breast development is the main end point. This article adds to studies providing the unsettling findings that the age of onset of breast development, in synch with, though not entirely explained by, the “obesity epidemic,” has continued to drop. It will inspire continued investigations of causes and implications for psychosocial public health. Remedies will follow.

The 1997 cross-sectional Pediatric Research in Office Settings (PROS) study on 17 000 US girls, followed by nationally representative data from the National Health and Nutrition Examination Survey III (NHANES), reported earlier...

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