Research has proven that exposure to asbestos is a cause of lung cancer in humans. Cigarette smoking is another known cause of lung cancer. However, the combination of asbestos exposure and smoking is far more likely to cause lung cancer than either factor by itself. This is known as the 'synergistic effect of asbestos exposure and cigarette smoking.'
Generally, when a person is exposed to two different carcinogens, the respective risk factors are added together to determine the cumulative risk factor from being exposed to both carcinogens. However, for asbestos and smoking, these risk factors when combined actually have a multiplicative effect, so that the factors are multiplied to determine the overall risk factor from being exposed to both carcinogens.
As a result of this synergistic and multiplicative risk effect, it has been shown that smokers who were exposed to asbestos have a 50 to 90 times greater risk of developing lung cancer than non-smokers who were not exposed to asbestos. This makes it that much more important for anybody who has been exposed to asbestos to quit smoking.
Besides lung cancer, the other most common cancer caused by asbestos exposure is mesothelioma. In contrast to lung cancer, research has shown that cigarette smoking has no relationship to a person's risk of developing mesothelioma.