Cigarette smoke transforms healthy saliva into a deadly cocktail that can accelerate mouth cancer, according to new research in the British Journal of Cancer.
Normally, saliva provides a protective buffer between toxins and the lining of the mouth because it contains important enzymes that fight and neutralise harmful substances.
But the new research shows that the chemicals in tobacco smoke combine with saliva with devastating effect. They destroy the protective components of saliva – leaving a corrosive mix that damages cells in the mouth and can eventually turn them cancerous.
There are nearly 8,000 cases and 3,000 deaths from mouth cancer* in the UK every year – the main cause being smoking. The researchers in this study wanted to examine saliva's role in the development of mouth cancer.
The study recreated the effects of cigarette smoke on cancerous cells of the mouth. Half of the cell samples were exposed to cigarette smoke and the other half to the saliva and cigarette smoke mixture.
Cancerous cells were used in order to quickly assess whether the saliva and smoke mixture would speed the cancer's development.
The study revealed that the longer the mouth cells were exposed to the contaminated saliva, the more the cells were damaged.
Dr Rafi Nagler, based at the Technion-Israel Institute of Technology, who co-led the study, says: "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.
"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. Cigarette smoke is not only damaging on its own, it can turn the body against itself."
Saliva contains anti-oxidants. These are molecules that can help protect the body against cancer. The researchers found that the cigarette smoke destroyed them and turned saliva into a dangerous cocktail of chemicals that could accelerate the development of mouth cancer.
Jean King, Director of Tobacco Control for Cancer Research UK, which owns the British Journal of Cancer, says: "It is World No Tobacco Day this week and once more we see the dreadful impact smoking can have on health.
"This insight into how mouth cancer can develop offers more reasons for smokers to try and quit. People know of the link with lung cancer, and this research adds compelling evidence about the damage smoking can do to the mouth."
* These figures refer to cancers of the head and neck, which include nose, mouth, lips, tongue, gums, tonsils, pharynx and larynx cancer.