It appears that girls are experiencing puberty at a younger age than they did in the past.
Starting in the 90’s, researchers began documenting that girls were starting to develop breasts around the age of 10, which was more than a year earlier than had been recorded in the previous medical literature. The same study noted that black girls were starting puberty even earlier, at around age 9 on average.
That study wasn’t a one-off. Researchers began monitoring the trend over the following decades in countries around the world, and that body of research points to a worldwide trend. In many countries, the puberty age for girls appears to have decreased by about three months each decade since the 70s. The same trend has been seen in boys, but less dramatic.
Early puberty in girls is associated with an increased risk of anxiety, depression, substance abuse, and other issues compared to those who reach puberty later. It’s also been linked to some cancers if they start menstruating earlier than others.
A definitive answer as to why this is happening is hard to pin down, but researchers have identified three factors that are likely contributing to the issue: body weight, stress, and exposure to certain chemicals.
Obesity is a main factor, and that’s been shown in various studies. One theory is that fat cells are known to produce a variety of hormones, some of which may trigger body processes that stimulate the onset of puberty. Fat cells aren’t inherently bad, and this is part of a normal healthy developmental process, however, it may be an issue when girls accumulate high levels of body fat at an early age, but researchers believe that can’t be the full explanation because plenty of girls start puberty early who are not overweight.
Another possibility could be chemicals. A 2009 study of almost 1,000 young girls in Copenhagen discovered that the average age of breast tissue attainment was much earlier in the group of girls from 2006 compared to 1991. The 2006 cohort were starting puberty more than a year earlier than their 1991 counterparts.
The doctor behind that study hypothesized that chemicals could be part of the change. He said that the girls with the earliest development of breasts in the study also had the highest level of phthalates in their urine. Phthalates are found in a lot of plastics and in some hair products, and they have long been on researchers’ radar as possibly harmful.
Phthalates are part of a wider group of chemicals known as “endocrine disruptors,” which can also impact hormones. Although various studies have looked at this, they’ve had a hard time drawing a definitive link between specific chemicals and early puberty.
There is some preliminary evidence that girls who experience sexual abuse early in life may be at increased risk for earlier puberty, but it’s hard to establish a causal link.
Researchers have also identified a few other interesting correlations. For example, it’s more common for a girl to have early puberty if her mom has a history of mood disorders, or if she doesn’t live with her biological father. Again, it’s hard to establish causality, but sustained stress may be the common factor.
One very interesting study that implicates stress is an Italian study published in February. It looked at the number of kids who presented with suspected precocious puberty at five pediatric endocrinology offices in Italy in 2020, compared to 2019. The study found that only 140 girls presented with precocious puberty symptoms in 2019, compared to 328 in 2020, meaning the number of girls presenting with these symptoms more than doubled in 2020. The researchers also established a link between confirmed precocious puberty in girls and a sedentary lifestyle as well as greater use of electronic devices.