The risk of lung cancer is also increased in people who work in the manufacturing of certain industrial gases, pharmaceuticals, soaps and detergents, paints, inorganic pigments, plastics, and synthetic rubber. The risk of developing lung cancer is related to the amount of exposure to the cancer causing agent. For example, the risk of lung cancer in humans is proportional to the number of cigarettes smoked. The risk of developing lung cancer is 8-20 times greater in smokers compared to people who have never smoked. A smaller, but real risk exists for cigar and pipe smokers.
Some cancer causing agents react together to significantly worsen the risk of developing cancer.
The combined exposure to asbestos and tobacco smoke clearly multiplies the risk of developing lung cancer. The risk of lung cancer is greater for those living in urban areas. This risk is approximately 1.2 to 2.3 times that of people living in rural areas. There is also an increased risk of lung cancer in smokers whose close relatives have had lung cancer. Scarring in the lungs from previous infections or injury can be associated with and increased risk of cancer.