Some of the chemicals in plastics alter the brains of baby boys, and make them 'more feminine', according to American researchers.
Male children exposed to high doses in the womb went on to be less likely to play with traditional boys' toys such as cars or to join in any rough-and-tumble games, they found.
The latest work from the University of Rochester's team adds to existing concerns about the safety of phthalates, which can be found in vinyl flooring and PVC shower curtains.
Phthalates are able to disrupt certain hormones, and have been banned in toys in the EU for some years. However, they are still widely used in many different household items, including plastic furniture and packaging. There are many different types and some of them mimic the female hormone oestrogen.
The same researchers have already shown that this can result in boys being born with genital abnormalities. They now say that certain phthalates also impact on the child's developing brain by knocking out the action of the male hormone testosterone.
Dr Shanna Swan and her team tested urine samples from mothers more than halfway through pregnancy for traces of phthalates. The women, who gave birth to 74 boys and 71 girls, were followed up when their children were aged four to seven and asked about the toys the youngsters played with and the games they enjoyed.
They found that two phthalates, DEHP and DBP, can affect play behaviour. Boys exposed to high levels of these in the womb were less likely than other boys to play with cars, trains and guns or engage in the 'rougher' games such as playfighting.
Elizabeth Salter-Green, director of the chemicals campaign group CHEM Trust, said the results were worrying.
"We now know that phthalates, to which we are all constantly exposed, are extremely worrying from a health perspective, leading to disruption of male reproduction health and, it appears, male behaviour too.
"This feminising capacity of phthalates makes them true 'gender benders'."
She did acknowledge that the boys who have been studied were still young, but she said that reduced masculine play at this age might lead to other feminised developments in later life.
But Tim Edgar, of the European Council for Plasticisers and Intermediates, said: "We need to get some scientific experts to look at this study in more detail before we can make a proper judgement."
DBP has been banned from use in cosmetics, such as nail varnish, since 2005 in the EU.
17 Nov 2009 | 
Vitamin D - Mums Are In The Dark
