More than 600 additives can legally be added to tobacco products.
These include coffee extract, sugar, vanilla, cocoa, menthol, oil from clove stems, caramel and chorophyll, the compound that gives plants their green colour.
Many appear to be present simply to add flavour.
But they may also have more sinister effects. For example, cocoa when burned in a cigarette produces bromine gas that dilates the airways of the lung, and increases the body's ability to absorb nicotine.
View the ingredients in a Marlboro here. Looks like a soft drink and a candy bar all rolled into one.