A long-term study of mothers and children has revealed that chemicals found in common household products may be causing girls to enter puberty at younger ages. Phthalates, parabens, and phenols were all linked to earlier puberty in girls, with no significant effect found in boys.
Scented products such as perfumes, deodorants, and soaps often contain phthalates, while parabens are used as preservatives in some cosmetics and other personal care products. Phenols, such as triclosan and benzophenone-3, are used in many products like soap, toothpaste, and skin lotion to increase their shelf life.
Study lead author Dr. Kim Harley is an associate professor of Public Health at the University of California, Berkeley.
“We found evidence that some chemicals widely used in personal care products are associated with earlier puberty in girls,” said Dr. Harley. “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.”
“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.”
The research team analyzed data from pregnant women who participated in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) study between 1999-2000.
The pregnant mothers were interviewed at around 14 and 27 weeks, and urine samples were used to measure concentrations of phthalates, parabens, and phenols. The researchers followed up on the pubertal development of their children, including 179 girls and 159 boys, every nine months between the ages of 9 and 13.
Urine testing revealed that 90 percent of the samples had concentrations of all the chemicals that the experts tested for except for triclosan, which was found in up to 73 percent of the samples.
Every time phthalates doubled in concentration within the mother’s urine, the development of pubic hair advanced by 1.3 months in the girls. In addition, for every doubling of triclosan in the mother’s urine, the girls had their first menstrual period just under a month sooner.
The urine samples taken from the children at the age of nine showed that for every doubling in the level of parabens, the timing of breast development, pubic hair, and first menstrual period all advanced by around one month.
“We already suspect that certain chemicals that are widely used in personal care products – like phthalates, parabens and triclosan – are endocrine disruptors,” said Dr. Harley. “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. 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.”
According to Dr. Harley, one possible explanation for why the same link was not found in boys is that different hormonal reactions trigger puberty in boys.
“This is still an active area of research and more studies are needed,” said Dr. Harley. “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.”
The study is published in the journal Human Reproduction.