The ingredient is used in many products as an antibacterial
A chemical ingredient used in soaps, detergents, shampoos and toothpaste has been found to cause liver cancer in mice.
The ingredient, triclosan, is used in many products as an antibacterial.
The study, carried out by researchers from the University of California and funded by US Public Health Service grants, was published in the science journal, PNAS (the Proceedings of the National Academy of Sciences of the United States of America).
The research found that mice fed high amounts of triclosan daily for six months suffered liver damage and were more susceptible to liver tumours induced by other cancer-causing chemicals.
Triclosan [5-chloro-2-(2,4-dichlorophenoxy)phenol; TCS] is a synthetic, broad-spectrum antibacterial chemical used in a wide range of consumer products, including soaps, cosmetics, therapeutics and plastics. The general population, the researchers said, are exposed to triclosan because of its prevalence in a variety of daily care products, as well as through waterborne contamination. They say it is linked to a variety of health and environmental effects, and wanted to investigate the effect on the liver.
The research involved two groups of mice: one fed a normal diet and the other a diet supplemented with triclosan.
In a second experiment, the research team injected two groups of mice with a chemical that causes the development of cancerous liver tumours, to see whether giving triclosan (this time given in their drinking water) influenced the development of the tumours thereafter.
Animal studies require higher chemical concentrations than predicted for human exposure
The results suggested that triclosan increases liver cell proliferation, induces liver scarring and reactive oxygen species accumulation. Taken together, the team concluded this was a sign that triclosan damaged the liver cells, suggesting that they may be more likely to become cancerous.
Triclosan-treated mice had a higher tumour number, bigger tumour size and greater tumour incidence than mice given the tumour-promoting injection alone. The number of detectable liver cancers was around 4.5 times higher in triclosan-treated mice than in control mice.
Approximately 25% of mice receiving the tumour promoting injection only exhibited small cancerous nodules, whereas more than 80% of triclosan-treated mice developed tumours.
The researchers acknowledged that, 'animal studies require higher chemical concentrations than predicted for human exposure', but said their study, 'demonstrates that TCS [triclosan] acts as a HCC [liver cancer] tumour promoter and that the mechanism of TCS-induced mouse liver pathology [disease] may be relevant to humans'.
Dr Nick Plant, Reader in Molecular Toxicology at the University of Surrey, took issue with some of the conclusions of the study.
'The authors study only mice, and draw conclusion only on mice. Their comments on human health are very circumspect. As the authors state, it is difficult to assess if the dose that they use in mice is relevant to human exposure levels, but at a simple examination it appears to be much higher than I would expect to see in a human. This further complicates extrapolation to the human situation as we are not comparing equivalent exposures. It is not valid to state that the effect of triclosan in mice will occur in humans as well.'
It is difficult to assess if the dose that they use in mice is relevant to human exposure levels
Dr Oliver Jones, Lecturer in Analytical Chemistry at RMIT University Melbourne, added: 'The results of this study are certainly interesting but I do not think they are a cause for concern for human health. Firstly the mice used in the study were primed with a tumour promoting chemical before being exposed to triclosan (which humans would not be) and the concentrations of triclosan used were much higher than those found in the environment.'
The UK's Medicines and Healthcare products Regulatory Agency (MHRA) lists regulated products containing triclosan on its website, although this is not comprehensive because it contains only products that are classed as medicines, which are more strictly regulated in safety terms than non-medicine products.
The concerns about triclosan have resulted in an investigation by the US Food and Drug Administration (FDA), which said that it does not have enough safety evidence to recommend any 'change to its use in consumer products'.