Prenatal exposure to phthalates feminizes play in boys.

Nov 16, 2009

Swan, SH, F Liu, M Hines, RL Kruse, C Wang, JB Redmon, A Sparks and B. Weiss. 2009. Sex-typical play behaviour in boys may be feminized by maternal exposure to phthalates during pregnancy. International Journal of Andrology doi:10.1111/j.1365-2605.2009.01019.x.

Boys exposed to phthalates during pregnancy are less likely to choose “boy typical” toys such as trucks, suggesting that phthalates can alter brain development and gender-specific behaviors.

Every parent knows that gender influences how children play. Girls like dress up and dolls. Boys like trucks and toy guns. A new study conducted by a research group based at the University of Rochester School of Medicine has found that exposure to phthalates during fetal life may affect the emergence of these gender typical play behaviors in boys.

This is the first study to suggest a link between prenatal phthalate exposure and male behavior.

The researchers explored play behavior in 145 preschool aged children. Play behavior was examined in relation to their mothers’ phthalate exposure during pregnancy. Urine was obtained from the mothers while they were pregnant and phthalate levels were measured in those samples. Boys born to mothers with higher urine levels of phthalates chose to play with “boy typical” toys less often than boys born to mothers with lower urinary phthalate levels. No change in play behavior was seen in girls.

Play was assessed by asking the mothers to complete the Pre-School Activities Inventory questionnaire. This questionnaire has been used by numerous other researchers to examine the degree to which children play with “gender stereotypical” toys. It is a well validated test but requires that the mothers answer the questions honestly.

The study focused on two common phthalates, diethylhexyl phthalate (DEHP) and dibutyl phthalate (DBP). Both of these compounds are used in a wide range of household products and are of greatest concern to scientists because they have been shown to interfere with testosterone hormone in animal and human studies.

The results indicate that phthalates can interfere with testosterone during development leading to a less masculinized brain. Phthalates have long been suspected to be anti-androgens and the findings reported in this play behavior study are consistent with that hypothesis. They are also consistent with what has been reported by numerous groups in rodents emphasizing the importance of animal models for making predictions about human effects.

Although the sample size in this study is small, the study is unique because the phthalate levels were measured during prenatal life. In many epidemiology studies seeking to link human health effects to a compound, blood or urine samples are taken at the time the study is conduced. For sex typical behaviors like play, it is thought that exposure during fetal life, rather than in early childhood, has the potential to produce the most significant effects. Being able to compare play behavior to phthalate levels in maternal urine samples obtained during pregnancy makes this a particularly unique and powerful study.

Phthalates are actually a group of chemicals, and this study focuses on two: DEHP and DBP. Both are widely used, particularly in products made from polyvinyl chloride (PVC), food containers, soft toys, and flooring. Many personal care products including lotions, cosmetics, and nail polish also contain phthalates. Medical devices, including plastic tubing, is another source of human exposure to phthalates. Some products now claim to be “phthalate free” and many countries are phasing out the use of these endocrine disrupting chemicals.