Boys who were exposed to phthalates in the womb seem less interested in masculine play behavior.

RODALE NEWS, EMMAUS, PA—As much as we may assume that boys and girls are created equal, we're not. Our gender-specific brains are hardwired to develop different personality traits and preferences based on whether we're male or female. However, a new study published in the International Journal of Andrology finds that chemicals in plastic called phthalates may interfere with that process. The study found that boys exposed to higher phthalate levels prenatally were not as interested in masculine play behaviors—playing with trucks, play fighting, or exploring new things—as boys with moms who had fewer phthalates in their bodies.

Phthalates are plasticizers used in a variety of products, including vinyl shower curtains, vinyl flooring, synthetic fragrances, and toys, that keep plastics soft and artificial scents from dissipating too quickly. In plastic items, phthalates can constitute as much as 40 percent of the finished product. The chemicals are used so widely that biomonitoring data from the U.S. Centers for Disease Control and Prevention (CDC) suggest that all Americans have some level of them in our bodies at any given time. The chemicals have been found to interfere with estrogen and testosterone production, trigger asthma and allergies, and harm the liver, kidneys, and lungs.

THE DETAILS: Researchers from the University of Rochester used data from urine samples that had been collected from pregnant women for a prior study and analyzed at a CDC lab for nine kinds of phthalates. Four to seven years after the samples were collected, the researchers contacted 150 mothers for follow-up questions on their children's play behaviors, with a resulting sample of 74 boys and 71 girls. On a scale of one to five, the moms were asked to indicate how often their children played with things like trucks and dolls, whether they preferred play fighting, climbing, or playing house, and if the children liked to take risks or explore new surroundings, both of which are considered masculine play behaviors. They also tried to control for a parent's bias with a survey asking questions such as "What would you do if you had a boy who preferred toys that girls usually play with?"

While no associations were found between phthalate concentrations and play behaviors in girls, the researchers found that boys whose mothers had high prenatal levels of two particular phthalates, di-2-ethylhexyl phthalate (DEHP) and dibutyl phthalate (DBP), were less likely to engage in masculine play behaviors, and more likely to engage in gender-neutral activities, such as puzzles or games. However, the boys weren't frequently engaging in feminine play activities like dressing up or playing with dolls.