Why Are Girls Hitting Puberty Younger and Younger?

In 1860, the average age for puberty onset in girls was 16.6 years old. In the 1980s, the average age hovered around 12.5. But, about 20 years later in the early 2000s, that average age dropped to 10.5 years old. There’s a combination of possibilities that play into answering the question of why girls are hitting puberty younger and younger which has left pediatricians, endocrinologists, and lab researchers puzzled for decades.

What Is Puberty? 

Scientists have defined puberty as the developmental stage from childhood to adulthood in which the body undergoes a series of physiological changes triggered by an increase in sex hormones. Common signs of puberty in girls are breast development, changes in body odor, underarm and pubic hair growth, acne, and the beginning of menstruation. However, doctors normally use breast development as the marker of the start of puberty. Historically, most girls begin puberty between ages 8 and 13, but that age has dropped in recent decades. A rare condition called precocious puberty is diagnosed in girls who begin puberty before 8 years old. According to the Mayo Clinic in the early 2000s, there are less than 200,000 cases in the United States annually, however, that number is growing as the average age of puberty is plummeting. 

Originally, when researchers began digging into this question, they only found evidence of early puberty onset in girls in the United States, forcing them to believe that environmental factors were responsible for abnormally early puberty. Doctors around the world were calling this the “U.S. puberty boom.” However, about two decades later, girls in Denmark were suddenly following the same trend. A 2009 study performed in Copenhagen illustrated that breast development was beginning on average at age 10, rather than age 11, and girls were getting their periods about four months earlier than before. Italy, Turkey, India, and many other countries followed suit – making the puberty boom a global health issue.

Possible Causes

Obesity

The obesity theory has been used to explain the early onset of puberty since the 1970s. Scientists determined that not only did breast development begin at a younger age for the sampled overweight girls, but they also started menstruating earlier than their counterparts with lower BMIs. More specifically, scientists have blamed leptin, a hormone responsible for regulating appetite, sexual development, and reproduction, for the mass early onset of puberty. Because our fat cells create leptin, the more fat an individual has, the more leptin their body produces. While researchers don’t believe leptin can trigger puberty on its own, they did discover that in mice, a certain amount of leptin must be present in the body in order for puberty to begin. Studies have also shown that physical inactivity, often a byproduct of obesity, lowers melatonin levels in the brain and can cause premature puberty in girls. 

Exposure to Chemicals

After the 2009 study uncovering the puberty boom in Denmark, scientists began to doubt that obesity was the sole cause of early puberty. This is because the BMIs of Danish girls remained the same between the 1990s and 2009 studies. Researchers then pointed to endocrine-disrupting chemicals like phthalates as a possible explanation. The girls with the earliest periods also happened to have the highest amounts of phthalates in their urine. 

The girls with the earliest periods also had the highest amounts of phthalates in their urine. 

Endocrine disruptors encompass a collection of chemicals like phthalates, BPA, PFAS, dioxins, and more, which are commonly found in plastics, fertilizers, cosmetics, packaging, soy products, furniture, electrical equipment, and even some pharmaceutical products. Endocrine disruptors like these either mimic real hormones and trick our bodies into thinking hormone levels have changed, or they block hormone receptors, inhibiting hormonal processes from functioning properly. Any type of hormone disruption can be linked to early puberty, as well as a host of other health problems.

Lifestyle and Mental Health

Scientists are still working to pinpoint the exact role of emotional and mental health on puberty. The transition from childhood to adulthood is already an emotional one, and as a girl’s hormone levels rise, so does her moodiness. However, there have been correlations found between emotional trauma and early puberty. One study found that girls who were victims of sexual abuse at a young age entered puberty earlier than their peers. According to New York Times research, girls whose mothers are predisposed to mood disorders are more likely to begin puberty younger, and girls who do not live with their biological fathers were also at risk for early puberty. These discoveries lead researchers to believe that mental health, trauma, and stress can also play a role in the onset of puberty.

Further, some research claims that nutrition and diet can impact puberty. Scientists have found that girls who eat a nutrient-lacking diet and girls who consume increased amounts of animal products have been found to enter puberty at a younger age. This evidence is closely intertwined with the chemical theory, as processed foods often have endocrine-disrupting chemicals in them. Premature puberty studies that were conducted throughout the pandemic show that increasingly sedentary lifestyles, stressors of Covid-19, and the use of electronic devices could have triggered the GnRH pulsatile secretion, which leads to early puberty onset. All of this information makes a strong case for lifestyle factors playing a major role in the age that a girl begins puberty.

Genetics and Racial Factors

Of course, there are countless genetic factors that play a large role in when a girl begins puberty. Scientists have discovered that African American and Hispanic girls are predisposed to reaching puberty at a younger age – some even begin puberty at age 6 or 7. Some suggest that this could be because of their genetic composition or the possibility that these racial groups are subjected to more emotional trauma, nutrient-lacking diet, and chemical exposure than their white counterparts. Still, some scientists claim that in up to 90% of girls, the cause of premature puberty is unknown.

In up to 90% of girls, the cause of premature puberty is unknown.

Health Implications of Early Puberty

In researching the causes of abnormally early puberty, doctors have dug into the possible effects as well. Premature puberty is associated with increased risks of breast and ovarian cancer, obesity, adult-onset diabetes, thyroid disorders, abnormal brain structure, stunted growth, and other physical health conditions. It’s possible that it’s also linked to increased mental health disorders like depression and substance abuse. 

However, just because a girl begins puberty before age 8 does not mean that her health is doomed for the rest of her adult life. It’s important to note that early puberty onset only slightly increases the risk for the previously mentioned health problems. Some doctors believe that precocious puberty is more damaging to the parents’ stress levels than to the child’s actual health. However, children with precocious puberty disorder may undergo brain scans to monitor hormone and neurological activity, or they may be prescribed medication for delaying sexual development. 

Closing Thoughts

There’s no single cause for the early puberty trend in girls around the world. Instead, researchers point to several factors that could impact puberty onset such as the obesity, endocrine-disrupting chemical exposure, lifestyle, and genetics theories that were discussed. While there are health implications for early puberty, there are also medications and treatments to help stop premature puberty if needed. Further, many girls diagnosed with precocious puberty end up as completely normal and healthy adults. 

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