Tiny fibres used to strengthen everyday products such as bicycle frames and hockey sticks could pose health hazards to those involved in their manufacture.
Certain types of carbon nanotubes - cylindrical molecules about one-thousandth of the width of a human hair - could cause cancer in the lining of the lung, University of Edinburgh researchers have found.
The study in mice found that while short carbon nanotubes appeared relatively harmless if they entered lung cavities, longer nanotubes were more likely to get stuck there and ultimately cause a type of cancer known as mesothelioma.
Researchers are now looking at assessing the level of risk involved, for instance by looking at how many of the long fibres are present in the air of workplaces.
The study, published in the American Journal of Pathology, found that longer carbon nanotubes caused a reaction in the lung lining similar to that of asbestos.
Professor Ken Donaldson, Chair of Respiratory Toxicology at the University of Edinburgh, said: "The industrial-scale manufacture of carbon nanotubes is increasing, with a global market in excess of £1 billion. This research shows that there is a potential hazard in the manufacture of certain types of carbon nanotubes."
Longer asbestos fibres are also more harmful than shorter fibres since they also get stuck in the lung cavity where they can cause diseases including mesothelioma.
The study demonstrates the need for industry to design safe nanofibres that are long enough to be useful but short enough to avoid causing disease.
It follows on from previous research in mice looking at the effect of carbon nanotubes on the stomach cavity.