Smoking involves burning a substance like tobacco and inhaling the smoke. Cigarettes are the most common smoking method. Cigarette smoke contains nicotine, which is highly addictive, tar containing cancer-causing chemicals, and carbon monoxide which reduces oxygen in the blood. Smoking causes numerous diseases like lung cancer, heart disease, and COPD. Secondhand smoke also increases health risks for non-smokers like lung cancer and heart disease. Smoking is responsible for many preventable deaths worldwide each year.