The most common cause of lung cancer is smoking.

Smoking causes lung cancer because there are substances within tobacco that are known to cause cancer. These substances are known as carcinogens (which means “cancer-causing agents”), and it is these carcinogens that cause the actual damage to the cells in the lungs. A cell that is damaged may become cancerous over a period of time.

One cannot predict which smoker is at greater risk of developing lung cancer. In general, though, a smoker’s chances of developing cancer depends on:

 
• The age that the person began smoking  
• How long the person has smoked  
• How many cigarettes per day the person smokes

Passive smoking - breathing in someone else’s smoke - may also increase the risk for developing lung cancer.

There are other causes of lung cancer not related to smoking. People who smoke and who also are exposed to these other causes have an even higher risk for lung cancer.

These other causes include:

 
• Exposure to cancer-causing agents through a person’s job. This includes exposure to asbestos, either in the mining or construction industries. Inhaled asbestos particles may remain in the lungs, damaging lung cells. It also includes exposure to certain industrial substances like coal products, vinyl chloride, nickel chromate, arsenic, and exposure to some organic chemicals like chloromethyl ethers.  
• Exposure to radiation, either through one’s occupation or for medical reasons, such as repeated x-rays.  
• Radon gas, which occurs naturally in rocks and soil in certain areas, may cause lung damage and may eventually result in lung cancer if it seeps into your home. The presence of radon in the home can be measured using an inexpensive kit that can be purchased at department or hardware stores.

Research suggests that some people are more at risk for developing cancer if their body is not as easily able to deal with certain cancer-causing chemicals. This inability to neutralize cancer-causing chemicals is believed to be inherited.

Researchers also believe that in some people, when they come into contact with certain cancer-causing agents, their immune system, instead of neutralizing them, will actually make these agents more aggressive within the body. Such people, therefore, would be more sensitive to tobacco smoke and chemicals known to cause cancer.