Why are girls starting puberty so early and what can parents do to support them? 

The age at which girls first begin to develop breasts is dropping. We ask experts why this is happening and what parents can do to support their children
Why are girls starting puberty so early and what can parents do to support them? 

Early puberty is a reality for many families. Picture: iStock 

She’s lining up her dolls, ready to play her favourite game. This morning you showed her how to use a sanitary pad. Not quite 11, your daughter has just got her first period. You weren’t expecting it so early.

Many girls are hitting puberty earlier than their counterparts of just a few generations ago. The first sign of puberty in girls is breast-budding – or thelarche, to use the medical term – and the age at which it starts has dropped worldwide by almost three months per decade from 1977 to 2013.

This is according to a systematic review of a plethora of studies conducted across the decades since the 1970s (exa.mn/Puberty-Worldwide-Trends).

In the 1990s, in North Carolina, Marcia Herman-Giddens began analysing data on the level of sexual maturation in three to 12-year-old girls, collected from more than 200 clinicians in paediatric practices across the US. Her 1997 study with the American Academy of Pediatrics created waves in the medical community because it found the average age of breast-budding was earlier than expected – 8.8 years for black girls and 9.9 for white. The discovery was highly controversial at a time when medics believed the average age of puberty for girls was 11-plus years.

Here, the Growing Up in Ireland, National Longitudinal Study of Children (Social-Emotional and Behavioural Outcomes in Early Adolescence) 2021, asked more than 3,300 13-year-olds if they had experienced their first period – and if so, at what age. Menstruation typically starts two to two and a half years after breast development begins.

The study’s author, Professor Elizabeth Nixon, associate professor in psychology at TCD, found that 72% of the 13-year-olds had already had their first period. Among the girls who had started, the average age of menstruation-onset was 12 years and three months.


                            Professor Elizabeth Nixon, associate professor in psychology, TCD. 
Professor Elizabeth Nixon, associate professor in psychology, TCD. 

“The study categorised girls as to whether they were on time, late starters or had started earlier, relative to everybody who’d had a period. The youngest age of onset was eight years and seven months. Out of the sample of 3,329 girls, about one-third were early starters,” says Nixon.

Precocious puberty 

Dr Declan Cody, consultant in paediatric endocrinology at Children’s Health Ireland (CHI), Crumlin, says the onset of puberty can be described in one of four ways: delayed, normal, early or precocious. “If a girl shows breast development under age eight it is termed precocious puberty,” he says, adding that it is usually girls – rather than boys – who present with this.

Dr Cody typically sees 10 to 15 new cases of precocious puberty a year, with referrals from girls aged three to seven years from anywhere in Ireland. “We do a hormonal evaluation. We also do a brain MRI to ensure there’s no abnormality predisposing the child to precocious puberty. In most cases, there isn’t.”

Medical treatment for precocious puberty is hormonal blockers – an injection given every three months by the family GP. This stops signals from the pituitary stimulating the girl’s ovaries. In this way, it prevents puberty advancing until the child reaches an appropriate age.

“We block precocious puberty for two reasons,” says Dr Cody. “If breast development begins at five or six years, the girl would have a period around age eight, which is very young and socially very challenging for the girl herself, the family and the school.”

The other reason has to do with growth potential, which is limited once menstruation starts. “If girls start puberty earlier than age eight, they lose out on that period of childhood growth. They could lose a significant amount of centimetres in stature.”

But, precocious puberty aside, it still remains that a substantial proportion of girls are experiencing pubertal-onset significantly earlier than many of their peers. Various reasons have been put forward for why this might be. It has been partly attributed to excess body fat accumulation (exa.mn/Puberty-Body-Fat).

In one study, conducted over decades, of almost 1,200 girls in Louisiana, obesity in childhood was linked to earlier onset of periods. Published in 2003, the study found a girl had twice the chance of having a period before age 12 “for each standard deviation above the average childhood weight”.

But obesity is not always an underlying factor – many early starters are not overweight. Anders Juul, professor of Growth and Reproduction at Rigshospitalet, a specialised hospital in Denmark, reported in 2009 a ‘recent decline in age at breast development’, after evaluating almost 1,000 school-aged girls. The Copenhagen Puberty Study found the average age for acquiring glandular breast tissue had dropped to 9.8 years by 2006 – a year sooner than in a 1991 cohort of girls they’d studied. However, BMI was not found to be relevant – BMI wasn’t any different in the 2006 group to the 1990s cohort.

Psychologists have also suggested that the timing of puberty could be influenced by psychosocial stressors. American child psychologist Jay Belsky first proposed this in 1991. Using data from a longitudinal study of 16-year-old girls, he concluded that family conflict and father absence in childhood predicted earlier age of menstruation-onset.

In the Annual Review of Psychology (2019), Bruce Ellis, a professor in the Department of Psychology at the University of Utah, pointed to “a substantial body of literature” that indicates early exposures to childhood adversities tend to predict earlier pubertal development in females. The stressors include socioeconomic adversity, child maltreatment, lack of family warmth and supportiveness, heightened parent–child conflict and father absence. (See: exa.mn/Puberty-Stress)

Endocrine-disrupting chemicals

In recent decades, concern has also grown that endocrine-disrupting chemicals (EDCs) could be playing a role in earlier pubertal onset. A 2018-published study from University of California, Berkeley, found prenatal exposure to chemicals in personal care products may speed puberty in girls (exa.mn/Puberty-Prenatal-Exposure).  Researchers followed 338 children from before birth to adolescence. They found that the daughters of mothers who had higher levels of chemicals, including diethyl phthalate, in their bodies during pregnancy experienced puberty at younger ages. Diethyl phthalate is often used in fragrances and cosmetics. 

However, in a review article published this April, Professor Juul and a team of researchers analysed 23 studies that looked at EDCs and their effect on puberty. Their conclusion: evidence is “too scarce to firmly confirm EDC exposure as a risk factor for changes in age of pubertal onset in the general child population”.

So the jury may be out on what definitively is causing earlier puberty – but it’s very clear that experiencing puberty significantly sooner than peers has consequences. Elizabeth Nixon, in the Growing Up in Ireland study, compared outcomes for early-starters with those who were on-time or late-maturers. She found being an early maturer was associated with higher depressed mood and anxiety, as well as antisocial behaviour.

“I also found early-maturing girls were more likely to have had an alcoholic drink in the past year than the other two groups. They were also more likely to have smoked.”


The early starter is very likely not developmentally ready – socially, cognitively and emotionally – for the biological leap her body is making. “If a girl is biologically mature but still behind cognitively and socially, there’s a mismatch across the different spheres. The girl isn’t ready in the other domains to cope with the advance in the physiological side,” says Nixon.

But the picture isn’t quite so simple, and nothing is set in stone for the early starter. Because when Nixon controlled for – and included in her analysis – the quality of the early starter’s relationships with her parents and peer group, she found the influence of pubertal status dropped.

“The key driver for these children’s wellbeing is not being early or late maturers. The key driver is the relationships within their context. If the girl is protected by positive relationships, the elevated risk of being an early maturer decreases.”

Nixon cautions however that having older friends can negatively impact an early starter. Such young girls were more likely to show greater antisocial behaviour, higher levels of smoking/drinking/drug use and greater depressed mood. “If a girl looks physically more mature and grown-up, she might start associating with a 15 or 16-year-old peer group, who are experimenting with boys, trying alcohol and smoking. And these older teens might have expectations of her that she isn’t ready for. Not being able to cope emotionally with these experiences can lead to anxiety and depression.”

Shock of early puberty 

Dr Claire Crowe, a senior paediatric clinical psychologist and member of the Psychological Society of Ireland.
Dr Claire Crowe, a senior paediatric clinical psychologist and member of the Psychological Society of Ireland.

Dr Claire Crowe, a senior paediatric clinical psychologist and member of the Psychological Society of Ireland, points out that adolescence, no matter when it starts, is hard for children to negotiate. “Part of the negotiation is to be in line with your peers. So a child who goes into puberty earlier has it harder – there’s already something setting them apart.”

Crowe, who works with the paediatric endocrinology team at CHI, Tallaght, says early puberty is a normal part of development for some girls, but it can be a shock for parents who mightn’t have expected it so soon – they can feel suddenly launched into their child’s adolescent phase. “I recall one mother saying she never thought she’d have to explain to her daughter about periods before telling her about Santa.”

Pointing out that parents recognise the value of childhood and want their child to experience it for as long as possible, Crowe says: “We really want our child to maximise that young, innocent, prolonged childhood. Early puberty can feel like there are new expectations and demands on the child.”

But it’s important to remember, she says, that puberty is still a process. “Physically, changes are happening but everything doesn’t come at once. We can still maintain that childhood experience for the child. Just because puberty has started doesn’t mean they have to stop playing with their younger toys.”

Early puberty is a reality for many families. What’s important is to be aware, says Nixon. “Puberty is often underway long before the event of menstruation. If your nine-year-old has become a bit withdrawn or volatile, do consider they may have entered puberty.”

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