Smoking is classified as the single most preventable cause of more than 400,000 premature deaths in this country each year. Tobacco smoke, which contains over 4,000 chemicals, including more than 50 cancer-causing elements, contributes to heart disease, cancer, stroke and chronic lower respiratory diseases — the four leading causes of death in the U.S. No tobacco product is safe. Cigarettes, cigars, pipes and smokeless tobacco contain nicotine and tar and pose a health hazard.