What's IN cigarettes that's so BAD?

A burning cigarette puts out particles, gasses and liquids. Only the solid particles -- about 5-8 percent of the cigarette's output -- are visible. The list of ingredients in tobacco smoke includes the following: nicotine, carbon monoxide, vinyl chloride, hydrogen cyanide, radionuclides, benzene, arsenic... in all, more than 4,000 different chemical compounds, including toxic heavy metals and pesticides.

More than 50 of these substances are known carcinogens. Others are known or suspected mutagens, capable of causing permanent, often harmful changes in the genetic material of living cells. Where do the chemicals come from? About half the compounds are found naturally in the green tobacco leaf and half are created by chemical reactions when tobacco is burned, Some are introduced during the curing process; others are added by manufacturers to impart a distinctive flavor or quality to their product. Here are some examples of what smokers inhale in each puff:

Carbon monoxide (CO):
An invisible, odorless gas. Car exhaust is a major source of CO; tobacco smoke is another. At high concentrations, CO starves the body of oxygen. Prolonged exposure at low doses can lead to cardiovascular disease.

Tar:
A sticky, black residue containing hundreds of chemicals, some of which are classed as hazardous waste.

Ammonia:
A caustic agent used in fertilizers and bathroom cleaners. Ammonia can increase susceptibility to viral illness and aggravate chronic respiratory conditions.

Hydrogen Cyanide (cyanide):
A colorless gas that smells like bitter almonds. It is among the most toxic chemicals found in tobacco smoke. Short-term exposure can lead to headaches, dizziness, nausea and vomiting.

Lead:
A "heavy" metal. Severe lead poisoning can cause birth defects and learning disabilities in children. Studies have shown that children who live with a smoking parent have more lead in their blood than children living in the vicinity of a lead smelter.