"Chemicals found in perfume, hand creams and body lotion may make girls go through puberty months early," reports the Mail Online.
Researchers in California looked at levels of chemicals commonly found in personal care and household products, in pregnant women and then in their children at age 9. The children were assessed regularly for milestones of puberty (such as development of breasts, pubic hair and testes, and menstrual periods) from age 9 to 13. Girls who'd been exposed to higher levels of chemicals in the womb or at age 9 reached some milestones up to 2 months earlier.
Earlier puberty has been linked to a slightly raised chance of breast and ovarian cancer in girls, and testicular cancer in boys.
Chemicals involved were: diethyl phthalate, triclosan, methyl paraben and propyl paraben, and 2 products formed by the breakdown of triclosan. Phthalates are found in some scented products such as perfumes, shampoos and deodorants, while parabens are used as preservatives in some cosmetics, and triclosan is an antibacterial agent used in some hand soaps and toothpaste.
The study does not prove that the chemicals were the cause, however. The associations between chemicals at age 9 and earlier puberty could be because children who reach puberty earlier may be more likely to use personal care products and cosmetics.
There are treatments available that can "pause" puberty and sexual development. Their use is typically only recommended if it is thought that early puberty could lead to emotional or physical problems which could then cause significant distress.
Where did the story come from?
The researchers who carried out the study were from the University of California, Kaiser Permanente health insurance company and the National Center for Environmental Health, all in the US. It was funded by the National Institute of Environmental Health Sciences and the US Environmental Protection Agency and published in the peer-reviewed medical journal Human Reproduction.
Most of the UK media reported the study in an accurate and balanced way, making it clear that the researchers had not proven that the chemicals studied brought on puberty earlier.
What kind of research was this?
This was a cohort study which tracked children from before birth until age 13. Cohort studies are good ways to spot patterns and links between factors, such as between exposure to chemicals and development of puberty. However, they can't prove that one factor causes another, and other factors could also be at work.
What did the research involve?
Researchers recruited pregnant women from an agricultural area of California, during 1999 to 2000. Women gave 2 urine samples which were tested for a range of chemicals. They were also interviewed about their age, education, ethnic background, household income and body mass index (BMI) before pregnancy. Researchers began studying their children at age 9, when 338 children gave urine samples and were weighed and measured, then examined to see if they had met puberty milestones such as pubic hair growth, and in girls, breast development. The examinations were repeated every 18 months until the children were 13. There were 179 girls and 159 boys in the study.
The researchers looked to see if the age of reaching puberty milestones was linked to the mother's level of chemicals during pregnancy, or the child's level of chemicals aged 9.
They tested the women and children's urine for the following types of chemicals:
- monoethyl phthalate (a component of diethyl phthalate found in some scented products), mono-n-butyl phthalate (a component of di-n-butyl phthalate found in some cosmetics and nail polish) and mono-isobutyl phthalate (a component of di-isobutyl phthalate found in some cosmetics and nail polish)
- methyl paraben and propyl paraben, used as preservatives in some cosmetics
- triclosan and 2.4 and 2.5 dichlorophenol, phenols used in some hand soap and toothpaste, and benzophenone-3, used in some sunscreens and cosmetics
They examined children for development of breasts, male genitalia, pubic hair and asked girls about the start of their period. The figures were adjusted to account for the body mass index (BMI) of the children and their mothers, as obesity has been linked to earlier puberty.
What were the basic results?
More than 90% of the urine samples showed signs of all chemicals tested for, except triclosan, which was found in 73% of mothers' samples and 69% of children's samples. Girls started their periods on average at age 11.7.
In girls, researchers found exposure to certain chemicals during their mother's pregnancy was linked to earlier puberty:
- each doubling of monoethyl phthalate was linked to a 1.3 month earlier development of pubic hair in their daughters (95% confidence interval (CI) -2.5 to -0.1)
- each doubling of triclosan was linked to a 0.7 month earlier start of menstrual periods in their daughters (95% CI -1.2 to -0.2) and each doubling of 2.4 dichlorophenol to a 0.8 month earlier start (95% CI -1.6 to 0.0)
No such findings were made for boys.
For girls and boys, researchers found exposure to different chemicals at age 9 was linked to earlier puberty:
- for girls, each doubling of methyl paraben was linked to a 1.1 month earlier development of breasts (95% CI -2.1 to 0.0), a 1.5 month earlier development of pubic hair (95% CI -2.5 to -0.4) and a 0.9 month earlier start to menstrual periods (95% CI -1.6 to -0.1)
- for boys, each doubling of propyl paraben was linked to a 1 month earlier development of testes and genitals (95% CI -1.8 to -0.1)
How did the researchers interpret the results?
The researchers said: "We found evidence that prenatal [pre-birth] and peripubertal [around the time of puberty] exposure to certain phthalates, parabens and phenols present in personal care and consumer products was associated with pubertal timing in girls, but less so in boys."
This research adds to evidence that some chemicals in household products may be having an effect on human hormones and could help to explain why puberty has been getting earlier in recent decades. As the study shows, most people are exposed to these chemicals and they are hard to avoid.
However, the study has some major limitations that mean we should be cautious about the results. Because it's an observational study, we don't know for sure that the chemicals are the cause of earlier puberty. That's especially true when we consider the results involving samples taken from children aged 9, when earlier puberty could be the reason for children using more cosmetics or personal care products, rather than the other way around. But other factors in the environment might also have an effect, such as agricultural chemicals used in this farming community.
The study only looked at 3 samples of chemicals, 2 during pregnancy and 1 in childhood, so we don't know if those results were typical of the children's exposure. It's notable that some of the results were quite close to not being statistically significant (meaning they could have come about by chance) and that the results for chemicals during pregnancy and in childhood differed.
Earlier puberty is likely to have many causes, including children being less likely to be undernourished or malnourished than in the past. This study adds useful new evidence to help researchers find out more, but it does not mean we should all change our behaviour to avoid personal care products.
If you do start to notice changes in your child that suggest they are in the first stages of puberty the best thing you can probably do is to explain what physical and emotional changes they should expect in the future.
Read more about the stages of puberty in girls and boys.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Mail Online, 4 December 2018
Sky News, 4 December 2018
The Sun, 4 December 2018
Metro, 4 December 2018
ITV News, 4 December 2018
The Times (subscription required), 4 December 2018
Links to the science
Human Reproduction. Published online December 4 2018