November 3, 2022 - 10:30am

The age at which a girl first starts her period can reveal a great deal about both her physical health and her social context. 

In Western countries, the average age at menarche fell from 16.5 years in 1840 to 13 in the 1990s. Most medical historians believe this to have been the result of improved nutrition and reduced impact of infectious disease in childhood. The richer societies became, the earlier girls began puberty.

But, peculiarly, since the turn of the century that relationship between affluence and age at menarche has gone into reverse. Now it is girls of lower socioeconomic status who get their periods first. 

A piece last week in the New Yorker, titled ‘Why More and More Girls Are Hitting Puberty Early’, attributed the rise in early menarche to several factors. Among these were rising obesity levels, less sleep triggered by increased technology use, and a spike in stress triggered by the Covid-19 pandemic. 

I’m sceptical of this last claim (as if the far more lethal pandemics of the past were free from stress!), but there is certainly good evidence that high calorie intake is associated with earlier menarche, along with a range of social factors. 

We have known since the 1980s, for instance, that girls in Western countries who grow up without a father at home begin puberty earlier. This link between fatherlessness and early sexual development is likely a result of the fact that, as one group of researchers puts it, “during human evolutionary history, when girls encountered familial conditions that were unfavourable for survival (e.g., insecure and unsupportive family relationships), it was adaptive to become reproductively mature earlier.” 

Perhaps unsurprisingly, given the political implications, the New Yorker piece does not mention this fatherlessness factor. And although there is a brief discussion of the possibility that “endocrine-disrupting chemicals found in food, plastics, and personal-care products” may be affecting girls’ (and boys’) sexual development, there is also no mention of the role that hormonal birth control might be playing in this story. 

Here is a scientific theory that you might be familiar with by way of Alex Jones. In 2010, the infamous shock jock announced that the US government was intentionally putting chemicals into the water supply with the goal of feminising American men. “It’s a chemical warfare operation,” Jones told his listeners, “I don’t like ’em putting chemicals in the water that TURN THE FREAKIN’ FROGS GAY!” 

His interpretation of the research may have been some way off, but there was a grain of truth in Jones’s theory. This was presumably sourced from some of the perfectly legitimate research indicating that male amphibians show physiological signs of feminisation when exposed to synthetic oestrogen. The oestrogen, in turn, is introduced to their environment via the urine of women using hormonal birth control. 

Although we know for sure that synthetic oestrogen is found in the urine of women using hormonal birth control, we don’t know exactly what effect its diluted presence in tap water might be having on human, rather than amphibian, health. Still, it is likely to be having some effect, including on sexual development, given that exposure to high levels of environmental oestrogen seems to be associated with early puberty in girls. 

Blaming hormonal birth control or fatherlessness for these mysterious and slightly alarming physiological changes is difficult to write about in a progressive publication like the New Yorker. But then, as so often, ‘the science’ — if pursued honestly — does not always produce politically palatable results.


Louise Perry is a freelance writer and campaigner against sexual violence.

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