"Our results suggest the need for further research and great caution before introducing such products into the market if long-term harm is to be avoided," Ken Donaldson, a researcher at the University of Edinburgh, and colleagues wrote.

Carbon nanotubes are molecular-scale structures made from carbon graphite used as a very strong, lightweight material for building, structural engineering, aerospace and a host of other purposes, including tennis racquets and baseball bats.

But since the discovery of the structures nearly 20 years ago, researchers have wondered about the health risks of the material. This is especially important as the global carbon nanotube market is expected to hit $1 billion by 2014.

A particular worry is whether carbon nanotubes behave in the same way as asbestos, widely used in the 20th century until the material was shown to cause a cancer of the lung lining that can take decades to appear following exposure.

The researchers injected different types of nanotubes into the abdominal cavity of mice and found that the long, straight ones caused inflammation and lesions that can lead to cancer.

But the study suggested short or curly carbon nanotubes did not have the same effect, indicating that products using the materials can be made to be safe, the researchers said.

They also said it was unclear whether enough inhaled carbon nanotubes could reach the mesothelium -- a protective sac that covers the body's internal organs -- to cause cancer, because they injected the structures into the mice's abdominal cavity.

Most people who develop mesothelioma have worked on jobs where they inhaled asbestos particles.

"This is a wake-up call for nanotechnology in general and carbon nanotubes in particular," said Andrew Maynard, a researcher at the Woodrow Wilson Centre for Scholars in Washington, who worked on the study.

"As a society, we cannot afford not to exploit this incredible material but neither can we afford to get it wrong -- as we did with asbestos."