A long-running study of mothers and children has found that chemicals widely used in shampoo, deodorant, nail polish and cosmetics are linked to early onset puberty in girls, which could heighten their health risks later in life.
The study found chemicals such as phthalates, parabens and phenols were all associated with earlier puberty in girls – some by bringing on earlier growth of pubic hair, others by causing an earlier start to menstruation.
There was no similar association observed in boys.
University of California public health associate professor Dr Kim Harley led the study, and suspects the chemicals are acting as endocrine disruptors – meaning they mimic, block or otherwise interfere with natural hormones.
In laboratory studies, the chemicals have been shown to cause earlier puberty in rats, but there were very few studies in humans.
The chemicals and where they’re found
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.
One of the first studies in utero
In a prepared statement, Dr Harley said: “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.”
Specifically, Dr Harley and her team found 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,” she said.
Dr Harley said the findings were significant because the age at which puberty starts in girls has been getting earlier in the past few decades – and 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 a lifespan.
“One hypothesis is that chemicals in the environment might be playing a role, and our findings support this idea,” she said.
Study tackles theory
Dr Harley and her colleagues analysed data from pregnant women who enrolled in the Centre for the Health Assessment of Mothers and Children of Salinas study between 1999-2000. They followed 338 of their children from birth to adolescence.
While the mothers were pregnant they were interviewed at 14 and 27 weeks’ 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 nine and 13.
More than 90 per cent of urine samples showed concentrations of all the chemicals, apart from triclosan, which was detected in 73 per cent samples taken from the pregnant mothers and in 69 per cent of samples taken from the nine-year-old children.
More of the chemicals, earlier the onset
For every doubling in the concentrations of an indicator for phthalates called monoethyl phthalate 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 just less than a month.
When the researchers looked at the urine samples taken from the children at age nine, they found 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.
Dr Harley said a possible reason why the association was not seen in boys was because different hormonal mechanisms are involved in boys’ puberty.
The effects of the chemicals on oestrogen may be why girls are more affected.
The study was conducted in mainly Latino women, living in farm-working communities in California, US. Most had no high school diploma and lived below the federal poverty threshold.
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 chemicals, such as pesticides encountered during farm working, might also have affected the results.