The chemicals in cigarette smoke come from the tobacco plant itself, its surroundings, the manufacturing process, and burning the cigarette.

The tobacco plant itself

Nicotine is found naturally in the tobacco plant. It is a neurotoxin (a poison that kills nerve cells) and the plant uses it to stop animals from eating it.

The soil

Tobacco plants absorb various chemicals from the soil and fertilisers. These become stored in the leaves and are released when the leaves are burned. These chemicals include metals like cadmium, arsenic and chromium.

The air

Tobacco plants have large leaves with sticky hairs called trichomes. These hairs can capture chemicals such as radioactive polonium-210 from the atmosphere, building up higher concentrations than other plants.

The leaves can also absorb and concentrate chemicals used in fertilisers and pesticides.

Processing

Some dangerous chemicals are formed when tobacco leaves are processed and cigarettes are manufactured.

For example, when tobacco is cured to remove moisture from the leaves, bacteria produce nitrites that react with chemicals in the leaves. This produces most of the nitrosamines in the final product. Many of these chemicals are unique to tobacco and not found in other plants.

Burning

Most of the dangerous chemicals in tobacco smoke are formed through the many chemical reactions that occur as the cigarette burns.

Burning organic material such as tobacco leaves produces polycyclic aromatic hydrocarbons. And sugars that are added to cigarettes produce formaldehyde when burned.

Additives

Hundreds of chemicals are added to cigarettes in order to make them taste nicer and easier to smoke. This include the irritating gas, ammonia, which can increase the addictive power of nicotine.

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