Chemicals used in plastics could be "feminising" the brains of baby boys, a study published today has suggested.
Research into pregnant women has shown those with a higher concentration of two phthalates in their urine produced sons less likely to play with male toys such as trucks and games like play-fighting.
The study, led by the University of Rochester Medical Centre and published in the International Journal of Andrology, examined the play of 145 pre-school children.
Phthalates are chemicals used to soften plastics and recent studies have shown that the major source of human exposure to the two phthalates of most concern - di(2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate, (DBP) - is through food, the researchers said.
The study showed higher concentrations of metabolites of DEHP and DBP were associated with less "male-typical" behaviour in boys in a play questionnaire.
No other phthalate metabolites measured in the womb was linked to the less-masculine behaviour and girls' play was not associated with phthalate levels in their mothers.
Earlier studies by the lead author of the study, Professor Shanna Swan, and others have shown that phthalate exposure during pregnancy might affect the development of genitals of both male rodents and baby boys.
Commenting on the latest research, Prof Swann said: "Our results need to be confirmed, but are intriguing on several fronts."
"Not only are they consistent with our prior findings that link phthalates to altered male genital development, but they also are compatible with current knowledge about how hormones mold sex differences in the brain, and thus behaviour. We have more work to do, but the implications are potentially profound."