Smoking

Smoking is by far the leading cause of lung cancer. Cancer develops when some event, such as smoking, damages the genetic code of normal cells and dismantles the body's natural defense against cancer. One reason why lung cancer is so deadly is that it can hide for years without symptoms. By the time it is discovered, it may have already spread to the brain, liver, bones or other organs. But lung cancer isn't the only cancer caused by smoking. Researchers have also linked smoking to cancers of the mouth, throat, pancreas, blood, cervix, kidney and bladder, and it is a major cause of emphysema, chronic bronchitis, stroke and heart disease.

Researchers separate smoking into two phases, a gas phase and a solid phase. Oxidants, including free radicals produced by cigarette smoke, can damage the genetic code. Studies suggest that they alter DNA, protein and lipids (fats). The damage to DNA may be irreparable, leading to the development of cancer. Mutated

cells reproduce rapidly, forming clumps of cells (tumors) that continue to grow and spread. It is difficult to stop smoking because tobacco smokers eventually become addicted to nicotine. Researchers have found that the physiology of the nicotine-addicted brain is similar to that of the cocaine- and heroin-addicted brain.