Nicotine is an addictive drug found naturally in tobacco. Other chemicals in tobacco plants may come from fertilizers or insecticides used in the growing process or from contaminants in air, soil, or water. Some chemicals are added when tobacco is cured; others are added in the manufacturing process.

Hundreds of ingredients are used in manufacturing cigarettes to make them more acceptable to the consumer. Additives make cigarettes milder and easier to inhale, improve taste, prolong burning, and increase shelf life. Laboratory analyses have shown that tobacco smoke contains more than 4,000 chemicals.