Boys exposed to high levels of phthalates in the womb are less likely than other boys to play with cars, trains, and guns or engage in "rougher" games like play fighting. These chemicals, used in the manufacturing of many plastics, have the ability to disrupt hormones, some by mimicking the female hormone estrogen. Previous research has also linked prenatal(胎児期の)exposure to the compounds to impaired genital development in boys. This recent study, which measured phthalate levels in the urine of pregnant mothers and later evaluated their children’s style of play, suggests that early exposure to these chemicals can have a long-term influence on gender identity and play behaviors.