The exact mechanism of lung cancer development is not fully elucidated. Smoking is the number one contributor to lung cancer, but there are many other factors that increase the risk of lung cancer in nonsmokers, including secondhand smoke, radon gas in the environment, some occupational exposures to carcinogens (such as asbestos, arsenic, chromium, nickel, beryllium, coal tar, mustard gas, trichloromethyl ether, chloromethyl ether, heating products from tobacco, and radon gas from the decay of radioactive materials such as uranium and radium, ionizing radiation and microwave radiation, etc.), the kitchen fumes, atmospheric pollution, etc. There may be other risk factors that have not been revealed yet. Avoiding these harmful exposures can help reduce the risk of getting lung cancer.