Researchers have found a substance in smokeless tobacco that causes oral cancer.

Previous research has shown that smokeless tobacco increases risk of oral cancer, cancer of the esophagus and pancreas. However, this is the first time that a carcinogen has been found that causes a cancer.

The carcinogen is called (S)-NNN, which belongs to a family of compounds called nitrosamines that are known to cause cancer. Nitrosamines are present in certain foods but the level of nitrosamines found in smokeless tobacco is far higher than levels found in food.

"This is the first example of a strong oral cavity carcinogen that's in smokeless tobacco. Our results are very important in regard to the growing use of smokeless tobacco in the world, especially among younger people who think it is a safer form of tobacco than cigarettes. We now have the identity of the only known strong oral carcinogen in these products," said lead author Stephen Hecht, PhD, from the University of Minnesota Cancer Center.

The study was conducted on rats. All the rats were given similar doses of the two forms of NNN, which they had suspected to be a cancer causing agent. The amount of NNN given to the rats was similar to a human consuming half a tin of smokeless tobacco for 30 years.

Researchers found (S)-NNN to be responsible for oral and esophageal cancer in study rats.

Previous studies on animals have shown that the cancer risk from smokeless tobacco was lower than the cancer risk from regular tobacco.

"The most popular brands of smokeless tobacco that are sold in the U.S. have unacceptably high levels of this particular carcinogen. And smokeless tobacco is a known cause of oral cancer. Obviously, we need to decrease the levels of this material in all smokeless tobacco products — or eliminate it altogether," said Hecht.

Hecht suggests that the carcinogen's level must be decreased to about one part per billion, which would make it comparable to the levels found in foods. He says that some companies already manufacture smokeless tobacco brands that have really low levels of this carcinogen.

The study was presented at the 244th National Meeting & Exposition of the American Chemical Society.