"What's in a cigarette?
Only a portion of the tobacco inside a cigarette comes from the leaf of a tobacco plant. A significant amount of the shredded brown innards of most modern cigarettes is a paper product called "reconstituted tobacco" or "homogenized sheet tobacco," which is made from a pulp of mashed tobacco stems and other parts of the tobacco leaf that would otherwise go to waste. Manufacturers spray and impregnate reconstituted tobacco paper with nicotine and other substances lost during the process, along with as many as 600 chemical additives. These include several that may come as a surprise, such as ammonia, which aids in the delivery of nicotine, and chocolate, which masks the bitter taste of tobacco. Finally, the 'recon' is sliced to resemble shredded leaf tobacco.
In addition to reconstituted tobacco, cigarette companies pack cigarettes with so-called puffed tobacco (also called "expanded tobacco"), which allows them to produce more cigarettes per pound of tobacco grown with lower levels of tar particles in the smoke. Manufacturers saturate this tobacco, which they make from the leaf of the plant, with freon and ammonia gases and then freeze-dry it. This process expands the tobacco, increasing its volume to at least double its natural state.
Though seemingly innocuous, cigarette paper is largely responsible for the rate at which a cigarette burns and the amount and density of the smoke it produces. The paper displays a pattern of concentric circle striations called "burn rings." The burn rings correspond to two different thicknesses in the paper, which serve to precisely control the speed at which the cigarette burns, slowing it automatically when the smoker is not inhaling in order to prolong the cigarette's consumption and speeding it up as the smoker takes a drag so as to maximize smoke intake. In addition, like the tobacco, the cigarette paper contains a host of chemicals, among them titanium oxide, which accelerates and maintains burning so the cigarette does not go out and the smoke is delivered evenly with each puff. These chemicals have contributed to many cigarette-caused fires, a problem that some manufacturers have not addressed until recently.
The filter cigarette was a specialty item until 1954, when manufacturers introduced it broadly following a spate of speculative announcements from doctors and researchers concerning a possible link between lung diseases and smoking. Reacting to smokers' voiced fears and sudden reduced cigarette consumption, cigarette companies, by altering the filter's structure and materials, began making competing claims about how low their brands' tar and nicotine levels were.
Some cigarettes today boast the inclusion of a "charcoal filter" in addition to the more common dense, synthetic fiber filters seen in almost all filter cigarettes. Manufacturers claim that charcoal filters, which contain bits of charcoal embedded within the fiber filters, reduce certain toxins in the smoke. But no evidence exists that these cigarettes are significantly less dangerous for the user.
Most filter cigarettes also bear ventilation holes punched around the circumference of the filter tip. (Regular cigarettes might feature one ring of ventilation holes, while light and ultra-light cigarettes of the same brand might have two or more rings.) These tiny holes, which you can see by holding the unrolled paper up to a bright light, can allow enough fresh air into the smoke that such cigarettes can test quite low in tar and nicotine levels when smoked by machines, which do not cover the holes. However, smokers' fingers or lips often cover some of these holes as they puff, giving them much higher doses of tar and nicotine than advertised. According to critics of the tobacco industry, the holes create a flexible dosing system that allows addicted smokers to maintain the tar and nicotine levels they crave while believing they are receiving lower, safer doses.
The above is extracted from the most excellent articles at PBS.org. The links below have superb graphics which illustrate the anatomy of a cigarette."
e em homenagem à aumenta filial d'a_boca na holanda, isto é o que eu fumo agora: