What exactly is it that causes lung cancer. is it the nicotine, the tobacco, or the smoke?

The smoke: It is the smoke that causes the lung cancer. The smoke causes an intense inflammatory reaction in the lungs, and when this continues for years and years, it can cause lung cancer. Now, the nicotine itself doesn't usually cause the cancer, but it is more addictive than heroin. Thus, you get hooked on the cigarettes, which have the smoke, which causes the cancer. A very, very sinister product.

Carcinogens: The burning and smoke contains bad irritants- carcinogens.