Constituents and emissions refer to the substances found in tobacco products and smoke. Cigarette smoke contains approximately 4,000 chemicals, including over 60 carcinogens and toxins, such as formaldehyde, benzene, and hydrogen cyanide. Although there is general agreement that cigarette packages should provide some information on these chemicals, regulators continue to struggle with how to best communicate this information in a feasible and meaningful way to consumers. Regulators have traditionally required manufactures to print the levels of three emissions (tar, nicotine, and carbon monoxide) on the side of packages. This remains the most common practice throughout the world.