Filter of cigarette
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.