Researchers have warned that a chemical commonly used in lipsticks, face washes and toothpaste can cause heart and muscle problems.
They have found that 'Triclosan', which is in hundreds of household products, can hinder the process by which muscles, including the heart, receive signals from the brain.
In tests on mice, they noted a 'dramatic' 25 per cent reduction in heart function within 20 minutes of exposure, and warned there is 'strong evidence' it could affect human health.
However regulators and other experts insist triclosan levels in products are safe, and that the doses injected into the mice were higher than those to which humans would ever be exposed.
Scientists had thought that the chemical - which was devised to prevent bacterial infections in hospitals - was metabolised quickly by the body without harmful effects.
However, the researchers at the University of California say it may remain active and be transported to organs, causing damage.
"These findings provide strong evidence that it is of concern to both human and environmental health," the Daily Mail quoted Professor Isaac Pessah, who led the study, as saying.
"For someone who is healthy a 10 per cent drop in heart function may not have an effect, but if you have heart disease it could make a big difference.' His team injected a group of mice with triclosan. They saw a 'significantly reduced' function in the heart's left ventricle within 20 minutes," he added.
Another test looked at the mice's skeletal muscles by getting them to grip wire mesh. Those injected in the past hour had an 18 per cent fall in their grip strength - although it was restored within a day.
By looking at muscle samples from mice in a test tube, the researchers believe the chemical disrupts the flow of calcium ions, which bring electrical signals from the brain to the muscles.
Under EU law, triclosan can be used in concentrations of up to 0.3 per cent in toothpastes and cosmetics.
The study has been published in the Proceedings of the National Academy of Sciences.