Chemicals in plastics are "feminizing" the brains of baby boys, a study shows.

Those exposed to high doses in the womb are less likely to play with "male" toys, such as cars, and are less willing to join rough-and-tumble games.The research adds to growing evidence hormone-disrupting chemicals in household products are interfering with the development of children.

The study, which looked at phthalates, chemicals that can mimic the female sex hormone oestrogen, is the first to link them to changes in behavior. Phthalates, used to soften plastics, are in household items such as plastic furniture, shoes, PVC flooring and shower curtains. They can also be transferred to food and drink from plastic packaging.

The study, published in the International Journal of Andrology, was led by Dr. Shanna Swan, professor of obstetrics and gynacology at the University of Rochester in New York State.

Her team tested urine samples from mothers in the 28th week of pregnancy for phthalates.The women, who gave birth to 74 boys and 71 girls, were contacted again when their children were aged four to seven and asked about the toys the youngsters played with, the activities they liked and their personalities.

The study found that phthalates were strongly linked with more feminine play in the boys, but had no impact on girls. Swan said believes the chemicals reduce levels of the male sex hormone testosterone in unborn babies, altering the development of the brain and male genitals.

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