Why are girls going through puberty earlier?

Global medical studies reveal that girls aged younger than 11 are starting puberty early, The Stack takes a look at why

By Hannah Connolly

7 March 2023

he medical community is divided as to what is causing the spike in early puberty among girls. Factors including blue light exposure, the use of hand sanitiser and obesity have all been cited. Medical professionals across the world are working to understand the root cause.

A recent study, carried out by a team of researchers in Seoul, South Korea in August 2022 revealed that the number of girls starting their periods before the age of eight had more than doubled since 2016, to 166,645 girls by 2021. In Germany, as reported in the New Scientist, a group of researchers carried out a representative study in one clinic. The findings showed that from 2015 to 2019, the number of girls referred for precocious puberty (PP), or early onset (as it is sometimes referred to as), had remained a constant at around ten cases a year. Then Covid-19 hit, and by 2020 that figure had more than doubled, and by 2021, it had risen to 30 total cases.

Elsewhere in Europe, reports paint a similar picture. An Italian group of researchers, who also published their findings across the past 12 months charted early onset within a group of 490 girls. Splitting them into two groups, those starting puberty early before the pandemic and those diagnosed during the pandemic. During the pandemic 338 girls were diagnosed with early onset PP. This was against just 152 girls diagnosed during the same time frame before the pandemic, representing a 122 per cent rise.

The studies (commissioned separately) examine the phenomena of precocious puberty, a medical term ascribed to a child who enters puberty before the average age. In girls this typically means the development of glandular breast tissue, known as thelerache, before the age of eight. According to the NHS, puberty tends to start between the ages of eight and 13, with the average age being 11. Puberty can include developing breast tissue and starting periods.

A second study in Turkey, examining the onset of Idiopathic CPP (the development of secondary sex characterises associated with puberty like body hair) found a similar pattern. Experts discovered a 46 per cent rise in girls presenting with Idiopathic CPP (the development of secondary sex characteristics associated with puberty like body hair) in 2020 against the previous two years.

The age at which girls reach puberty has been getting younger since the 1970s. In fact for every decade a three month drop in onset age has been observed according to the collective analysis of data from 30 different studies.

‘If you think about a girl having her first period, aged eight or nine in year four, that is quite a burden psychologically’

“There very much is a well-observed trend across the whole developed world, both in Europe and the US, and also in several Asian countries and Australia towards an earlier onset of puberty. That has been observed for several decades,” says Wellcome Trust clinical research career development fellow, senior lecturer at Queen Mary University and honorary consultant in paediatric endocrinology, Dr Sasha Howard. “I think what has got our attention, recently, is a real noticed increase post-covid and that has got quite a lot of interest from the research community as to why that change has happened.”

This means that girls are likely to begin puberty five years younger than their counterparts 10 years ago — the reason why has divided the medical community. “There are a lot of different explanations as to why there has been this long-term trend in the earlier tim- ing of puberty onset,” adds Dr Howard.

“We know that particularly a woman’s reproductive capacity is closely linked to how healthy she is, in terms of nutrition, and if you are underweight you will have a later timing of puberty and so the converse is also true.”

Some experts maintain that early onset can be caused by rising numbers of obesity - exacerbated by the pandemic lockdowns, others believe that exposure to certain chemicals - such as those found in some hand sanitisers are to blame. Rising stress levels among young girls have also been cited as a cause, and the NHS website cites that neurological problems or problems with ovaries or thyroid glands, or genetic disorders are proven causes of early onset. Though it also says: “early puberty mostly affects girls and often has no obvious cause”.


The National Childhood Measurement Programme recorded that obesity levels amongst reception age children had risen from 9.9 per cent to 14.4 per cent. The increase largely owing to stay at home orders and international lockdowns which lead to the closure of sports facilities and schools in the UK during 2020-21.

Combined analysis of studies pulled from medical journal PubMed, online medical resource Web of Science and medical research content platform EMBASE shows that childhood obesity was associated with significantly higher risks of early puberty largely for girls. The combined findings, which involved more than 13,338 girls, were released by Frontiers in Paediatrics.

One of the studies conducted by the Department of Human Development and Family Studies at the Pennsylvania State University assessed girls’ weight at the ages of five, seven and nine, and tracked against the development of breast tissue. The findings revealed that the girls with higher percent of body fat at age five and seven were more likely to be classified with earlier onset at nine than those with lower percentages of body fat.

In 2021, in the UK, researchers found that leptin, a hormone related by fat cells that limit hunger, has an impact on the part of the brain that regulates sexual development and could be a factor in the decreasing age of onset.

Chemical exposure

Another widely posited cause of early onset puberty is the exposure to chemicals. “There are studies that suggest it’s not all about weight, there are probably other factors that are leading to earlier timing of puberty and there has been quite a lot of interest in things that we describe as endocrine disrupting chemicals. So, pesticides and fertiliser, and all of the different plastics that we are exposed to,” says Dr Howard.

Diethyl phthalate, commonly found in perfumes and cosmetics, and only part banned in the EU in 2018, was linked by researchers at the University of California in 2018 to early puberty. Largely due to the chemicals disrupting the body’s hormonal oestrogen balance. The study tracked 338 girls from birth to adolescence as well as during the 14th to 27th week in utero, and revealed that children whose mothers who had been exposed to triclosan (a chemical found in hand sanitiser, handwashes and toothpaste) hit early puberty.

The presence of the chemical was measured in the mothers urine and suggested that daughters of those exposed to the highest levels went on to begin their periods four months earlier, on average, to the other girls included in the study.

In the wake of the pandemic, a study at the Jehangir Hospital in India, suggested that the indiscriminate use of sanitisers and the stress impact of the lockdowns could also be connected to the rise in early onset.

Revealing that referrals to the hospital for early onset had surged 3.6 times during the years of the pandemic. Dr Howard, however argues that tracking endocrine disrupting chemicals against puberty onset can prove problematic at a research level: “they are quite difficult to study because we are all exposed to lots of different endocrine disrupting chemicals throughout our life. It is quite difficult to hone down on which ones are important, and what the sort of reasonable or problematic dose might be.”

Blue light exposure

Another theory is that early puberty is caused by excessive exposure to blue light from mobile phones and computers - the use of which increased significantly among children during the pandemic. A study, conducted in Ankara, Turkey, and Presented at the 2022 60th Annual European Society for Paediatric Endocrinology meeting said that rodent groups exposed to the blue light had the early onset of puberty. In this study, Dr Aylin Kilinç Uğurlu and colleagues in Ankara, Turkey, used a rat model to investigate the effects of blue light exposure on reproductive hormone levels and the time of puberty onset. Female rats were divided into three groups of six and exposed to either a normal light cycle, six hours or 12 hours of blue light. The first signs of puberty occurred significantly earlier in both groups exposed to blue light, and the longer the duration of exposure, the earlier the onset of puberty. Rats exposed to blue light also had reduced melatonin levels and elevated levels of specific reproductive hormones (oestradiol and luteinising hormone), as well as physical changes in their ovarian tissue, all consistent with puberty onset. At the 12 hours exposure, rats also showed some signs of cell damage and inflammation in their ovaries.

In response to the study the UK Society of Endocrinology said: “According to an animal study, presented at the 60th Annual European Society for Paediatric Endocrinology meeting, higher levels of exposure to blue light may increase the risk of earlier puberty onset. The research suggests that blue light exposure from mobile device use may be a risk factor for earlier puberty onset in children and should be further investigated.”

During the pandemic, screen time increased significantly across all age groups globally, with the biggest increase seen in primary school children at 83 minutes more a day according to Anglia Ruskin University, which led the global study.

In 2015, a study by the UK Clinical Research Collaboration (UKCRC) using collected data, revealed that less than 2.5 per cent of publicly funded research in the UK is dedicated only to female reproductive health.

Dr Howard acknowledges funding into women’s health research is often overlooked: “I think it can be quite dismissed, and not that much attention given, but I think it is obviously very important for the patients themselves and the families. It can have quite a significant impact. If you think about a girl having her first period, aged eight or nine in year four, that is quite a burden psychologically.”

“Overall, there are very strong associations between, early puberty and really significant cardiovascular disorders, endocrine cancers, type two diabetes,” Dr Howard adds. “If we are looking after the health of our population, we also need to be paying attention to these things. That is not saying that every girl that has early puberty will have diabetes or hypertension high blood pressure, not at all but, in general as a population these things do make us more unhealthy and we do need to address obesity and weight in children, screen time, level of psychosocial stress that something like a lock down or pandemic will apply on children.”

Though the medical community remains fractured in their consensus of cause, Dr Howard says important work is being done by researchers to make waves in the diagnosis and treatment of early onset puberty.

“I think one of the really exciting things is that we are in this era of genomic discovery, understanding genes that govern when children go into puberty. We know that puberty hormones turn on, but we don’t really know how they know to turn on at the right time? Where we have made really quite exciting leaps forward in the last five to ten years, is in finding families where they have a change in one gene that has really changed their timing of puberty - so the whole family has really early timing of puberty. Then we can do a lot of in-depth molecular studies and work out what that gene does in the brain to turn puberty on. The treatments we have used haven’t really changed for quite a few years now, the way that we diagnose hasn’t really changed, but actually the future is there could be a lot more genetic diagnosis early on, and that we can be much more targeted in our approach to children and really understanding what the underlying problems are that have led them to have an early puberty and therefore treat them in a much more targeted way”.

The Short Stack

Global medical studies reveal that girls aged younger than 11 are starting puberty early The Stack takes a look at why

By Hannah Connolly

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