Editing Tobacco smoke (section)

== Safety ==
{{Main|Health effects of tobacco}}

Tobacco smoke, besides being an [[Irritation|irritant]] and significant [[indoor air pollution|indoor air pollutant]], is known to cause [[lung cancer]], [[heart disease]], [[chronic obstructive pulmonary disease]] (COPD), [[emphysema]], and other serious diseases in smokers (and in non-smokers as well). The actual mechanisms by which smoking can cause so many diseases remain largely unknown. Many attempts have been made to produce lung cancer in animals exposed to tobacco smoke by the inhalation route, without success. It is only by collecting the "tar" and repeatedly painting this on to mice that tumors are produced, and these tumors are very different from those tumors exhibited by smokers.<ref name="kapp" /> Tobacco smoke is associated with an increased risk of developing respiratory conditions such as [[bronchitis]], [[pneumonia]], and [[asthma]]. Tobacco smoke aerosols generated at temperatures below 400 °C did not test positive in the [[Ames test|Ames assay]].<ref name="a">{{citation | editor=Philip Wexler | author=C Lynn Humbertson | entry=Tobacco | title=Encyclopedia of Toxicology | edition=2nd | volume=4 | publisher=Elsevier | year=2005 | pages=197–200 | isbn=978-0-12-745354-5}}</ref>

In spite of all changes in cigarette design and manufacturing since the 1960s, the use of filters and "light" cigarettes has neither decreased the nicotine intake per cigarette, nor has it lowered the incidence of lung cancers ([[National Cancer Institute|NCI]], 2001; IARC 83, 2004; U.S. Surgeon General, 2004).<ref name="epidem">{{citation | editor1=Robert J. Mason | editor2=V. Courtney Broaddus | editor3=Thomas R. Martin | editor4=Talmadge E. King Jr. | editor5=Dean E. Schraufnagel | editor6=John F. Murray | editor7=Jay A. Nadel | title=Murray and Nadel's Textbook of Respiratory Medicine | author1=Anthony J. Alberg | author2=Jonathan M. Samet | chapter=Epidemiology of Lung Cancer | volume=1 | edition=5th | year=2010 | publisher=Saunders | isbn=978-1-4160-4710-0}}</ref> The shift over the years from higher- to lower-yield cigarettes may explain the change in the pathology of lung cancer. That is, the percentage of lung cancers that are [[adenocarcinoma]]s has increased, while the percentage of [[squamous cell cancer]]s has decreased. The change in tumor type is believed to reflect the higher [[tobacco-specific nitrosamines|nitrosamine]] delivery of lower-yield cigarettes and the increased depth or volume of inhalation of lower-yield cigarettes to compensate for lower level concentrations of nicotine in the smoke.<ref>{{citation | editor1=Robert J. Mason | editor2=V. Courtney Broaddus | editor3=Thomas R. Martin | editor4=Talmadge E. King Jr. | editor5=Dean E. Schraufnagel | editor6=John F. Murray | editor7=Jay A. Nadel | title=Murray and Nadel's Textbook of Respiratory Medicine | author1=Neal L. Benowitz | author2=Paul G. Brunetta | chapter=Smoking Hazards and Cessation | volume=1 | edition=5th | year=2010 | publisher=Saunders | isbn=978-1-4160-4710-0}}</ref>

In the United States, lung cancer incidence and mortality rates are particularly high among African American men. Lung cancer tends to be most common in developed countries, particularly in North America and Europe, and less common in developing countries, particularly in Africa and South America.<ref name="epidem" />{{clarify|is this a result of the longer-term trend of smoking in the developed world, or greater use of diagnostic testing to discover lung cancer, or some other reason?|date=April 2021}}