Smoking destroys protective molecules in saliva and transforms it into a dangerous cocktail of chemicals that increases the risk of mouth cancer, scientists said on Tuesday.

“Cigarette smoke is not only damaging on its own, it can turn the body against itself,” said Dr Rafi Nagler, of the Technion-Israel Institute of Technology in Haifa, Israel.

Saliva contains antioxidants, molecules that normally protect the body against cancer, but Nagler and his colleagues have discovered that cigarette smoke destroys the molecules and turns saliva into a dangerous compound.

“Our study shows that once exposed to cigarette smoke, our normally healthy saliva not only loses its beneficial qualities but it turns traitor and actually aids in destroying the cells of the mouth and oral cavity,” he added.

In research reported in the British Journal of Cancer, Nagler and his team studied the impact of cigarette smoke on cancerous cells in the laboratory.

Half of the cells were exposed to saliva exposed to cigarette smoke and the other half just to the smoke. Cells exposed to the saliva mixture had more damage and it increased along with the time of exposure.

“Most people will find it very shocking that the mixture of saliva and smoke is actually more lethal to cells in the mouth than cigarette smoke alone,” Nagler added in a statement.

Smoking and drinking are the leading causes of head and neck or oral cancers, which includes cancer of the lip, mouth, tongue, gums, larynx and pharynx. Nearly 400,000 new cases of the illness are diagnosed worldwide each year with the majority in developing countries. The five-year survival rates are less than 50 percent.

Nagler and his colleagues believe the research could open up new avenues to develop better treatments to prevent oral cancer.

“This insight into how mouth cancer can develop offers more reasons for smokers to try and quit,” said Jean King, of Cancer Research UK, which publishes the journal. “People know the link with lung cancer and this research adds compelling evidence about the damage smoking can do to the mouth.”

SOURCE: British Journal of Cancer, 2004.