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Shampoos, perfumes, deodorants, soaps and cosmetics, among others, may be contributing to girls entering puberty at earlier ages.

A new, long-running of mothers and children has found that chemicals used in聽personal care and household products could be causing early onset puberty.聽

Published in the journal , the study found that聽chemicals聽such as phthalates, parabens and phenols were all associated with earlier puberty in girls, although no similar association was observed in boys.

Some phthalates are used in scented products such as perfumes, deodorants, soaps, shampoo, nail polish and cosmetics; parabens are often used as preservatives in cosmetics and other personal care products; and phenols, which include triclosan and benzophenone-3, are used in soap, toothpaste, lipsticks, hairsprays, shampoos and skin lotion to increase the durability of the products.

Dr Kim Harley, Associate Professor in Public Health at the , Berkeley, USA, who led the study, said: 鈥淲e found evidence that some聽chemicals聽widely used in personal care products are associated with earlier puberty in girls. Specifically, we found that mothers who had higher levels of two聽chemicals聽in their bodies during pregnancy 鈥� diethyl phthalate, which is used in fragrance, and triclosan, which is an antibacterial agent in certain soaps and toothpaste 鈥� 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.

鈥淭his 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聽chemicals聽in the environment might be playing a role, and our findings support this idea.聽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.鈥�

Study methodology

Dr Harley and her colleagues analysed data from pregnant women who enrolled in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) study between 1999 and 2000. They followed 338 of their children from birth to adolescence. While the mothers were pregnant they were interviewed at around 14 and 27 weeks鈥� gestation and urine samples were taken in order to measure concentrations of phthalates, parabens and phenols. After birth, the researchers assessed pubertal development in the 179 girls and 159 boys at the age of nine and collected urine samples. Pubertal development was checked again every nine months between the ages of 9 and 13.

Over 90% of urine samples showed concentrations of all the聽chemicals聽tested for, apart from triclosan, which was detected in 73% of samples taken from the pregnant mothers and in 69% of samples taken from the nine-year-old children.

For every doubling in the concentrations of an indicator for phthalates called monoethyl phthalate (MEP) in the mothers鈥� urine, the development of pubic hair shifted 1.3 months earlier in girls. For every doubling of triclosan in the mothers鈥� urine, the timing of the girls鈥� first menstrual period shifted earlier by just under a month.

When the researchers looked at the urine samples taken from the children at the age of nine, they found that for every doubling in the concentrations of parabens, the timings of breast and pubic hair development and first menstrual period all shifted approximately one month earlier.

Findings and limitations

Dr Harley said: 鈥淲e already suspect that certain聽chemicals聽that are widely used in personal care products 鈥� like phthalates, parabens and triclosan 鈥� are endocrine disruptors. This means that they mimic, block or otherwise interfere with natural hormones in our bodies,聽such as oestrogen. In laboratory studies, these聽chemicals聽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.鈥�

She said a possible reason why the same association was not seen in boys was because different hormonal mechanisms are involved in boys鈥� puberty. The effects of the聽chemicals聽on oestrogen may be why girls are more affected.

The study was conducted in mainly Latino women, living in farm-working communities in California, USA; most had no high school diploma and lived below the US federal poverty threshold. When the researchers started the study 20 years ago, they were primarily interested in the effects of pesticides, which is why they chose this group of women. 鈥淏ut we always knew we would have the opportunity to examine other聽chemical聽exposures,鈥� Dr Harley explained.

One limitation of the study is that girls who start puberty early are more likely to start using personal care products, such as deodorants, which could be why parabens and phthalates showed in their urine. Exposure to other environmental聽chemicals, such as pesticides encountered during farm working, might also affect the results. A final limitation is that only one or two urine measurements were taken in the mothers and children, and regular measurements might have been better as indicators for phthalates, parabens and phenols only reflect exposure to them in the previous 24鈥�48 hours.

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

Most people are exposed to phthalates, parabens and phenols. A previous study, the National Health and Nutrition Examination Survey (NHANES) in the US, found that more than 96% of women taking part had detectable concentrations of these聽chemicals聽in their urine.

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