Nearly 85% of all lung cancers are associated with smoking. It is considered a direct and main cause. Smoke and carcinogens (cancer-causing agents) are inhaled into the lungs before they are absorbed into the bloodstream. Smokers regularly expose their lungs to carcinogens that irritate and damage cells that line the respiratory tract. This irritation and damage can alter the DNA of the cells, increasing the rate of cellular turnover. The risk of lung cancer increases with the number of years as a smoker and the number of cigarettes smoked. Smoking also includes other forms of tobacco found in pipes and cigars. Long-term exposure to secondhand smoke also contributes to an increased risk of lung cancer

Occupational or Environmental Exposures

Exposure to asbestos is associated with a specific type of lung cancer called mesothelioma. For people who work (or worked) with asbestos, the risk is even higher among those who smoke. Other lung irritants, such as wood smoke, burning coal, mine dust, metals, or paint also increase the risk of lung cancer. These exposures can occur in the workplace or at home.

Radon is a radioactive gas that occurs naturally in the soil. It is a colorless, odorless gas that seeps into buildings and homes. Long-term or heavy exposure to radon gas is associated with lung cancer risk. The risk is compounded in those who smoke.

Air pollutants, such as by-products from the combustion of diesel and other fossil fuels, are linked to lung cancer. Some people living outside of the US have an increased risk of lung cancer because of exposure to arsenic in drinking water.

Genetics and Family History

Some genes are inherited, while others are acquired. Genetic make-up can influence risk by:

  • Making it more difficult to break down carcinogens in the body
  • Making the lungs more vulnerable to the actions of carcinogens
  • Having cells that do not have a mechanism to keep them from multiplying in a controlled manner (like brakes on a car)
  • Having cells that have a mechanism that accelerates cellular growth beyond the normal rate (like a gas pedal on a car)
  • Missing or have a specific gene that causes these changes

People who have close family members, like parents, siblings, children, or other relatives, have a higher risk of lung cancer. The association is strongest in relatives who developed lung cancer at 60 years of age or younger.

Other medical conditions that may contribute

Medical conditions and/or treatments may increase the risk of lung cancer. This is because of inflammation, irritation, and scarring that cause lung damage. Some examples include: