A study has found chemicals in personal care products could be potentially associated with earlier onset of puberty in girls

A cohort study has looked into the potential impact that chemicals found in personal care products – such as perfumes, deodorants, soaps, shampoos and makeup – may have on hormones and puberty development.

Researchers enrolled pregnant women from California in 1999-2000 and measured concentrations of three phthalate metabolites, two parabens and four phenols in urine collected during their pregnancy.

They also measured the same chemicals in the women’s children when they reached nine years of age.

Pubertal timing was assessed among 179 girls and 159 boys every nine months between ages nine and 13.

With girls, earlier onset of pubic hair development was associated with higher prenatal urinary monoethyl phthalate (MEP) concentrations, and earlier first menstrual bleeding with associated with higher prenatal triclosan and phenol concentrations.

For every doubling in the concentrations of an indicator for MEP in the mothers’ urine, the development of pubic hair shifted 1.3 months earlier in girls.

For every doubling of triclosan in the mothers’ urine, the timing of the girls’ first menstrual period shifted earlier by nearly a month.

Researchers also observed earlier breast development, public hair development and first menstrual bleeding associated with higher methyl paraben concentrations in the girls at nine years old, and earlier first menstrual bleeding was also associated with higher propyl paraben at this age.

For every doubling in the concentrations of parabens at nine years old, the timings of breast and pubic hair development and first menstrual period all shifted approximately one month earlier.

In boys, the researchers observed no associations with prenatal urinary biomarker concentrations, and only one association of earlier genital development with propyl paraben at nine years old.

Lead author Dr Kim Harley, Associate Professor in Public Health at the University of California, Berkeley, US, said: “We found evidence that some chemicals widely used in personal care products are associated with earlier puberty in girls.”

“Specifically, we found that mothers who had higher levels of two chemicals in their bodies during pregnancy – diethyl phthalate, which is used in fragrance, and triclosan, which is an antibacterial agent in certain soaps and toothpaste – had daughters who entered puberty earlier.

“We also found that girls with higher levels of parabens in their bodies at the age of nine entered puberty earlier,” said Dr Harley.

“This is important because we know that the age at which puberty starts in girls has been getting earlier in the last few decades; one hypothesis is that chemicals in the environment might be playing a role, and our findings support this idea.

“Earlier puberty in girls increases their risk of mental health problems and risk-taking behaviour as teenagers and increases their risk of breast and ovarian cancer over the long-term, so this is an important issue to address.”

Dr Harley said the effects of the chemicals on oestrogen may explain why girls were more affected than boys.

“We already suspect that certain chemicals that are widely used in personal care products – like phthalates, parabens and triclosan – are endocrine disruptors. This means that they mimic, block or otherwise interfere with natural hormones in our bodies, such as oestrogen. In laboratory studies, these chemicals have been shown to cause earlier puberty in rats, but there are very few studies in humans,” said Dr Harley.

“Additionally, we know that endocrine-disrupting effects are particularly important during specific critical windows of development, such as in the womb or during puberty. This study is important because it is one of the first studies to look at human exposure in the womb and because it gives us a chance to examine exposures both in the womb and at puberty.”

However the authors point out that as the chemicals they looked at are quickly metabolised, one to two urinary measurements per developmental point may not accurately reflect usual exposure.

The results may also reflect reverse causality, they say, i.e. that children going through puberty early may be more likely to use personal care products.

Finally, the study population was limited to Latino children of low socioeconomic status living in a farmworker community, and therefore may not be widely generalisable.

More studies are needed, added Dr Harley.

The study was published in the journal Human Reproduction.