Chemicals found in household products such as deodorants, shampoo and perfumes have been linked to early puberty in girls, a new study suggests.
Experts found that chemicals in some personal care products were associated with girls starting puberty earlier than their peers.
However, the research found no association between chemicals and the start of puberty in boys.
Researchers studied 388 children in California who were taking part in a long-term study.
Pregnant women were enrolled to the study between 1999 and 2000.
The authors examined the levels of chemicals in the mothers during pregnancy and children when they were nine years old.
The study, which examined 179 girls and 159 boys, then tracked the onset of puberty.
The study, published in the journal Human Reproduction, examined chemical levels including phthalates, parabens and phenols.
Certain phthalates are used in some 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 can be used in soap, toothpaste, lipsticks, hairsprays, shampoos and skin lotions.
Dr Kim Harley, associate professor in public health at the University of California, who led the study, 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.
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.