MOST POPULAR HEALT CENTERS NEAR ME What happens when you smoke? Cigarette smoke is made up of 4000 chemicals that are present either as tiny particles or gases and about 50 are known to lead to cancer, the toxin nicotine being one of them. In addition to nicotine, the chemicals that make up cigarette smoke also include tar and carbon monoxide. Prolonged exposure to these toxins can hamper your body's ability to filter air and clean the lungs. The smoke not only irritates the lungs but also causes excess production of mucus.