This stuff in your mouth may increase lung cancer risk, even if you donât smoke Credit: CC0 Public Domain In a new study, researchers found that the type and abundance of bacteria found in the mouth may be linked to lung cancer risk in non-smokers. They found fewer species and high numbers of particular types of bacteria seem to be linked to heightened risk. The research was conducted by a team at the Albert Einstein College of Medicine. Around one in four cases of lung cancer occurs in non-smokers and known risk factors, such as secondhand tobacco smoke, background radon exposure, air pollution, and family history of lung cancer don’t fully explain these figures, say the researchers.