A chemical found in shampoo and hand lotions may damage the developing nervous system, research suggests.
Some shampoo contains a chemical that kills off bacteria
A US study found methylisothiazolinone (MIT) can affect the growth of parts of developing nerve cells which help them communicate with their neighbours.
The work, by the University of Pittsburgh, was carried out in rats, but researchers are concerned about the potential effect on human foetuses.
Details were presented to the American Society for Cell Biology.
Researcher Dr Elias Aizenman said: "While more research is needed to determine what effect MIT would have in rodent models, both at the cellular level and to a developing nervous system, our results thus far suggest there is a potential that everyday exposure to the chemical could also be harmful to humans.
Cell signalling structures
Axons: an extension from the cell body used for sending signals to other cells
Dendrites: Elaborate projections on the cells that receive incoming information
"I would be particularly concerned about occupational exposure in pregnant women and the possibility of risk to the foetus."
MIT is used to kill harmful bacteria that like to grow near moisture or water.
It is often used in personal care products like shampoos and hand lotions - but also in water cooling systems and in factories which need water for manufacturing.
However, Dr Aizenman said he had been unable to find any reports about the effect of the compound on the nervous system.
His team is now planning more research to help understand how MIT affects the development of cells.
The latest study found prolonged exposure to low levels of the chemical inhibited the development of nerve cell structures called dendrites and axons, which play key roles in enabling one cell to transmit signals to its neighbours.
MIT apparently blocked the function of an enzyme that is activated when cells come into contact with each other.
Dr Aizenman said: "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.
"I realise it's a big leap to suggest there may be a parallel between environmental exposure and the noticeably higher rates of diagnosed childhood developmental disabilities, but I would caution that based on our data, there very well could be neurodevelopmental consequences from MIT."
Dr Chris Flower, of the Cosmetics, Toiletries and Perfumery Association in the UK, said MIT had passed numerous safety tests and would continue to be used in a wide range of products.
He said: "There is no cause for concern. MIT has passed all the safety tests for use in these products."
Dr Flower said MIT was only used in combination with certain other chemicals in products in Europe.
But he said the European Commission's independent expert scientific committee
had reviewed all the data on MIT and concluded it was also safe to use on its own, with limits set on the maximum concentration.
Dr Flower said because MIT was a preservative, if it was introduced into certain cells in the lab it was bound to affect their growth in certain concentrations.
But he said the chemical had a good safety profile for the toiletries and cosmetics which people regularly used.
Dr Donald Peebles, an honorary consultant in obstetrics at University College London, told the BBC News website the findings could not be interpreted as showing MIT was dangerous in pregnant women - further research would be required to draw that conclusion.
The current study was based on cell cultures, he said. It would be interesting to see if similar results were produced by giving MIT to pregnant rats, and observing neuronal development in their offspring.
Dr Peebles said there were also question marks about what level of MIT was found in women who were regularly exposed to products which contained it, and where it was able to cross the placenta into the circulation of a developing foetus.