A chemical used in some shampoos, toothpastes and household cleaning products has been suspected of causing cancer. Triclosan, an antibacterial, appears to interfere with the body's ability to process toxic chemicals, and this may lead to liver cancer.
The theory has been met with scepticism by academia and the chemical industry because it has been based on experiments with laboratory mice-even though many manufacturers have stopped using it, and America's health regulator, the Food and Drug Administration (FDA), is considering an outright ban across the US.
In the UK, triclosan can be found in Dial antibacterial liquid hand soap, Dermalogica skin purifying wipes and Colgate's Total toothpaste, as well as in many household cleaning agents.
Researchers from the University of California, San Diego School of Medicine discovered triclosan's lethal effects after they fed it to laboratory mice for six months, equivalent to 18 human years. The mice fed the chemical developed larger, and more frequent, tumours than other mice.
The researchers accept that the doses fed to the mice were far higher than levels found in toothpaste and shampoo.
Despite their reservations, the FDA is reviewing the chemical, because it has also been associated with hormone disruption and muscle contraction.
(Source: Proceedings of the National Academy of Sciences, November 18, 2014; doi: 10.1073/pnas.1419119111)