Studies have shown a synergistic relationship between asbestos and tobacco smoke in the causation of lung cancer. The studies found that in approximately a third of the lung cancer cases where smokers had asbestos exposure, the lung cancer was attributable to the synergy of the two working together rather than either individual carcinogen. There are more than 60 carcinogens in cigarette smoke, and asbestos, also being carcinogen, has been proven to cause lung cancer much more frequently than either smoking or asbestos on their own. In fact, when a smoker is exposed to asbestos fibers, his or her risk of lung cancer increases by a factor of over 50.