Cigarette Smoking. This is the main cause of lung cancer. It is responsible for 90% of lung cancer deaths. With the increasing number of years of smoking, the number of cigarettes smoked each day and the tar and nicotine contents of the cigarettes; the risks of developing lung cancer will be increased. 

Pipe and Cigar Smoking. The risk of lung cancer is also increased in pipes and cigars smokers though less than those who smoke cigarette. 

Industrial Hazards. Exposure to certain workplace chemicals and minerals increase the risk of lung cancer e.g. asbestos, coal gas, chromates, nickel, arsenic, vinyl chloride, mustard gas, radon by-products of uranium mining and processing. Asbestos workers who also smoke increase their risks of developing lung cancer 60 times. 

Passive Smoking. Non-smoking wives who inhale their husbands smoke have a 35% higher risk of developing lung cancer.