Unborn children may be at risk from the shampoos and hand lotions used by their pregnant mothers, it was claimed yesterday.

A chemical commonly used in these toiletries can affect the growth of structures in the immature nerve cells of rats, according to researchers at Pittsburgh University in the United States.

Methylisothiazoline (Mit) could also harm the developing nervous systems of humans. The compound is used as a preservative in personal care products and, because it kills harmful bacteria growing near water, is used in water cooling systems and in factories using water in manufacturing.

Elias Aizenman, professor of neurobiology at Pittsburg, conceded that more work was needed but suggested that Mit inhibited the development of structures that were essential for transmitting signals between cells.

"This chemical is being used more and more extensively, yet there have been no neurotoxicity studies in humans to indicate what kind and at what level exposure is safe ... Based on our data, there very well could be neuro-developmental consequences from Mit."

Dr Aizenman said: "I would be particularly concerned about occupational exposure in pregnant women and the possibility of risk to the foetus."

The Cosmetics, Toiletries and Perfumery Association said Mit had passed numerous safety tests.

"People use these products every day. There is no cause for concern," its director general, Chris Flower, said. The EU commission had been advised that it was safe.