Girls who are exposed before birth to chemicals commonly found in cosmetics, soaps, shampoos and other personal care products may begin puberty at an earlier age, according to a study published this week in the journal Human Reproduction.
Specifically, the study found that the daughters of mothers who had higher levels of certain chemicals — particularly diethyl phthalate and triclosan — during pregnancy tended to experience puberty at a younger age. No similar association was observed in boys, however.
This finding supports growing evidence that everyday chemicals can disrupt hormones in the body in ways that can have an impact on when children experience puberty.
In recent decades, the onset of puberty has been occurring at progressively younger ages in girls (and possibly boys). This trend is troubling, for entering puberty at an earlier age has been linked to depression and risk-taking behaviors, as well as to a slightly increased increased risk of breast and ovarian cancer in girls and testicular cancer in boys.
Where the data came from
For the study, researchers at the University of California, Berkeley, used data from 388 children (179 girls and 159 boys) whose families were participating in the ongoing Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) study. Begun two decades ago to look at the impact of pesticide exposure on children’s development, the CHAMACOS study has since been expanded to focus on the effects of other chemicals as well.
The children’s mothers, who had been recruited into the study in 1999 and 2000, provided two urine samples during pregnancy. Those samples were tested for three type of chemicals: phthalates, which are often found in cosmetics, nail polish and some scented products like perfumes, soaps, deodorants and shampoos; parabens, which are used as preservatives in cosmetics; and phenols, including triclosan, which was added to soaps and body washes as an anti-bacterial ingredient until 2017, when the U.S. Food and Drug Administration (FDA) banned its use in such products because it was shown to be ineffective and possibly unsafe. Triclosan can still be found, however, in some cosmetics and toothpastes.
When the study’s children were 9 years old, their urine was tested for the chemicals as well. They were also weighed and then examined to see if they had met any of the developmental milestones marking different stages of puberty, such as pubic hair growth and, in girls, breast development and first menstrual period. The examinations were repeated every nine months until the children were 13.
Ninety percent of the urine samples of both mothers and children showed signs of all three types of chemicals — except for triclosan, which was present in 73 percent of the mothers’ samples and 69 percent of the children’s.
The girls in the study started their periods at 11.7 years, on average.
The researchers found strong associations between the levels of chemicals in the urine samples and early puberty. Each doubling of the concentrations of diethyl phthalate or triclosan in the mothers’ urine meant, for example, that their daughters developed pubic hair and started their menstrual periods about a month earlier, on average.
Girls with higher levels of methyl paraben in their urine at age 9 were also more likely to reach those puberty milestones early.
No association was found between the concentrations in the mothers’ urine and early puberty in boys, although boys who had higher levels of propyl paraben in their urine at age 9 tended to experience earlier growth of their penis and testes.
The study was observational, so it doesn’t prove that chemicals in personal care products cause early puberty. As the study’s authors point out, it could be that girls who reach puberty at a younger age are more likely to start using makeup, nail polish, deodorants and other such products earlier, too.
Also, the urine samples were taken and tested only three times (twice during pregnancy and once in childhood). The results of those tests may or may not have represented the children’s true exposure to the chemicals.
And, although the researchers did adjust their findings for the child’s weight (heavier girls tend to enter puberty earlier), other factors not accounted for in the study may also explain why some of the children experienced puberty at earlier ages.
Still, the findings can’t be dismissed, particularly since animal research has repeatedly shown that exposure to some of the same chemicals examined in this study can act as hormone-disruptors and induce early puberty.
“While more research is needed, people should be aware that there are chemicals in personal care products that may be disrupting the hormones in our bodies,” said Kim Harley, an associated adjunct professor at the UC-Berkeley’s School of Public Health, in a released statement.
“There has been increasing awareness of chemicals in personal care products and consumer demand for products with lower levels of chemicals,” she added. “Resources like the Environmental Work Group’s Skin Deep database or the Think Dirty App can help savvy consumers reduce their exposure.”
FMI: You’ll find the study on Human Reproduction’s website.