Cigarettes are a small roll of porous paper containing a rod of chopped up tobacco leaf. Cigarettes are designed so that the tobacco can be smoked, by lighting the cigarette and breathing in the smoke. At the mouth end of the cigarette there is second layer of porous paper (called tipping paper) and a filter. The tipping paper is designed to allow fresh air to infiltrate when the smoker inhales. This fresh air reduces the harshness of the smoke. The filter cools the smoke and reduces the flow of smoke out of the cigarette. Cigarettes also contain additives such as sugars and flavourings which are used to increase shelf life, control the rate at which the cigarette burns and controls the delivery of the chemicals.

Cigarette smoke contains over 4,000 different chemical compounds. Many of these are toxic, and at least 43 are known carcinogens (cancer-causing agents). Examples of known compunds found in cigarettes include: nicotine, carbon monoxide and tar.

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