Cigarettes contain chopped-up tobacco leaf blended from two main varieties: yellowish 'bright', also known as Virginia where it was originally grown, containing 2.5-3% nicotine; and burley tobacco which has a higher nicotine content of 3.5-5%.
Nicotine is as addictive as heroin and cocaine
Nicotine stimulates the central nervous system, increasing heart rate and blood pressure. In large quantities it is highly poisonous and can cause death by paralysing the muscles of respiration. At present there is no evidence that it is carcinogenic (cancer-causing).
Deprivation can lead to strong cravings accompanied by anxiety, irritability, hunger, restlessness and decreased concentration.
Nicotine has been reduced from an average of 2mg per cigarette in 1955-61 to about 0.9mg by 1996.
In addition to the leaf blend, cigarettes contain 'fillers' which are made from the stems and other bits of tobacco which would otherwise be waste products. These are mixed with water and various flavourings and additives.
Over 600 can legally be added to tobacco products to increase the addictiveness eg. chemicals may be used to enhance the alkaline content of smoke, increasing the nicotine hit and making it more addictive.
In 1997 there was a voluntary agreement to disclose all new additives and toxins. However, all additives prior to 1997 do not need to be disclosed.
All cigarettes produce tar but the brands differ in amounts. The average tar yield of British cigarettes has declined from about 30mg per cigarette in the period 1955-61 to 11mg today.
Tar contains known carcinogens. When heated it becomes brown and treacly in appearance; particles travel in the smoke to the lungs and respiratory system where they are gradually absorbed.
It is a mixture of many different chemicals that include cancer-causing agents formaldehyde, arsenic, cyanide, benzo[a]pyrene, benzene, toluene and acrolein.
From 1st January 1998, an upper limit of 12mg tar per cigarette was applied to all cigarettes sold in the EU (with the exception of Greece). Both the labelling and tar yield directives will be replaced by a new directive, currently going through the legislative process, which will place an upper limit of 10mg of tar, 10ml of carbon monoxide and 1mg of nicotine on all cigarettes sold in the EU.
Low tar cigarettes
Although there is a moderate reduction in lung-cancer risk associated with lower-tar cigarettes, research suggests that the assumed health advantages of switching to lower tar may be largely offset by the tendency of smokers to compensate for the reduction in nicotine (cigarettes lower in tar also tend to be lower in nicotine) by smoking more or inhaling more deeply.
Filters are made of cellulose acetate and trap some of the tar and smoke particles from the inhaled smoke. They also cool the smoke slightly, making it easier to inhale. They were added to cigarettes in the 1950's in response to the first reports that smoking was hazardous to health.
Nicotine and tar delivery can be modified by the type of paper used in the cigarette. Using more porous paper will let more air into the cigarette, diluting the smoke and (in theory) reducing the amount of tar and nicotine reaching the smoker's lungs.