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Early life exposure to certain endocrine disrupting chemicals (EDCs) commonly found in cosmetics and other household products was linked to early puberty in girls, but less so in boys, researchers reported.

In a longitudinal cohort study of Hispanic participants, both prenatal and peripubertal exposure to parabens, phthalates, and other EDCs found in makeup and soaps were linked to early development in young girls, written by Kim Harley, PhD, of University of California Berkeley, and colleagues, in .

The researchers found a twofold increase in mothers' urine biomarker concentrations for certain chemicals during pregnancy, which was associated with a significantly earlier average onset of pubarche (first appearance of pubic hair) and menarche (first menstruation) in girls, although wasn't tied to thelarche (first onset of breast development) (P<0.05 for all):

• Monoethyl phthalate: 1.3 month earlier pubarche (95% CI -2.5 to -0.1)
• Triclosan: 0.7 month earlier menarche (95% CI -1.2 to -0.2)
• 2,4-dichlorophenol: 0.8 month earlier menarche (95% CI -1.6 to 0.0)

However, elevated exposure to propyl paraben at age 9 was the only biomarker tied with a significantly early onset of gonadarche in boys (average 1.0 month earlier, 95% CI -1.8 to -0.1 months). None of the other environmental chemicals were tied to an earlier gonadarche or pubarche in boys.

The authors cautioned that study limitations included the fact that the children were all Latinos living in a farming community. Also, reverse causality was a possibility as children who experience early puberty may be more likely to use personal care products, they noted.

"We already suspect that certain chemicals that are widely used in personal care products -- like phthalates, parabens, and triclosan -- are endocrine disruptors," said Harley in a statement, explaining that these chemicals "mimic, block, or otherwise interfere with natural hormones in our bodies, such as estrogen."

"In laboratory studies, these chemicals have been shown to cause earlier puberty in rats, but there are very few studies in humans. 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," she stated.

Harley also noted that these chemicals are widely used in everyday products, with phthalates commonly used in fragrances and triclosan frequently appearing in soaps and toothpaste due to it's antibacterial properties.

Exposure to these chemicals outside the womb was also associated with early puberty in girls. Specifically, a twofold increase in urine concentrations for propyl paraben and 2,5-dichlorophenol at the age of 9 was associated with an 0.8 month (95% CI -1.6 to -0.1) and 1 month (95% CI 0.1-1.9) earlier onset of pubarche.

As for methyl paraben exposure in childhood, this was linked to a significantly earlier onset of thelarche, pubarche, and menarche:

• 1.1 month earlier thelarche (95% CI -2.1 to 0.0)
• 1.5 month earlier pubarche (95% CI -2.5 to -0.4)
• 0.9 month earlier menarche (95% CI -1.6 to -0.1)

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

The analysis included 338 children and their mothers residing in California, almost all of whom were Latina. During 1999 and 2000, urine samples of the pregnant mothers were analyzed for three phthalate metabolites, methyl paraben, and propyl paraben, as well as four phenols. At age 9, peripubertal urine samples were collected from the children to assess phenol and paraben levels. Phthalate levels weren't assessed in children due to budget constraints and a limitation of the findings. The children were followed up every 9 months during the ages of 9 and 13 to assess Tanner staging of development.

"This is still an active area of research and more studies are needed. However, we are concerned about evidence that some widely-used chemical in the products that we put on our bodies every day may be having an impact on hormonal and reproductive development," Harley concluded.

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