In November of this year, the University of Rochester Medical Center released data that has added to the growing concern over exposure to chemicals used in our everyday lives.
The study found that if a pregnant mother’s urine tested high for two common phthalates (chemicals used in plastics), her son was less likely to play in a typically male way – with trucks, or roughhousing, for example – at school age. The moms were tested at around 28 weeks gestation and researchers followed up with the families when the children were between three-and-a-half and six-and-a-half years old. Using a questionnaire, kids were rated by their parents on their preferred activities, choice of toys, and general character traits.
The boys whose mothers had higher levels of phthalates were less likely to engage in “boyish” activities, preferring gender-neutral toys like puzzles. Girls’ play behavior did not show any differences.
Phthalates are added to plastics to make them more flexible. When food is stored or heated in a phthalate-containing material, like polyvinyl chloride (PVC), the chemical makes its way into our bodies. Household products like soaps and lotions also contain phthalates and transfer through skin exposure. The chemicals have been under scrutiny because they are an anti-androgen, meaning that they inhibit the action of male hormones and may alter brain chemistry and sexual development. In 2008, the chemicals were banned from use in baby toys. A decade ago, the European Union eliminated phthalates from all toys for children under three.
The lead author of the study, Shanna Swan, Director of the University of Rochester Center for Reproductive Epidemiology, says that she suspects phthalates might interfere with testosterone production at a critical point, between eight and twenty-four weeks gestation when hormones are wiring up the male and female brain. The sexual development of rodents has been found to change under heavy phthalate influence. With this in mind, the group wanted to know if the disruption of brain chemistry in the womb might lead to observable differences later in life.
Of course the idea of “male typical” play is complicated. As Lise Eliot’s recent book Pink Brain, Blue Brain outlines, typical male and female play is hugely influenced by parents, teachers, and society. But Eliot also mentions striking findings from primate research that weigh in on the nature side. One-year-old boy vervet monkeys spend more time playing with a ball and a toy police car, while their girl counterparts spend more time with a rag doll and (oddly) a red cooking pot. The same phenomenon has been shown with rhesus monkeys. So play behavior does seem to be partly hardwired.
The results are a little unsettling, but not cause for panic. First of all, even the boys whose moms had been exposed to the highest levels of phthalates did not play drastically different than their peers. And remember the data is from a small sample based on parents’ reporting, so it’s subject to the biases of the moms and dads. The real concern is that there might be some underlying biological change caused by phthalates that we haven’t identified yet, or that reveals itself later in life. But that theory requires a lot more testing – Swan’s group is gearing up for a large-scale study to do just that. Stay tuned.