BMJ  2005;331:1425 (17 December), doi:10.1136/bmj.331.7530.1425-b

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Smoke from cigarette tip is more toxic than main inhaled smoke

Abergavenny

Unpublished research by the tobacco industry shows that inhaled "sidestream" cigarette smoke—the smoke that rises from the tip of the burning cigarette between puffs—is more toxic than the "mainstream" smoke inhaled by the smoker.

Lighting up: the smoke from someone else's cigarette may be more toxic than your own Credit: PAT SULLIVAN/AP/EMPICS

It found that inhaled fresh sidestream smoke, which makes up around 85% of secondhand smoke, is four times more toxic per gram of total particulate matter than inhaled mainstream smoke.

A report in Tobacco Control (2005;14: 396-404[Abstract/Free Full Text]) describing the research conducted by Philip Morris Tobacco in the 1980s says: "The tobacco industry has vigorously challenged the link between secondhand smoke and lung cancer, including funding of research published in 2003 challenging the evidence linking secondhand smoke and lung cancer. However, while it publicly challenged the link, Philip Morris Co privately performed extensive in vivo toxicological testing of sidestream smoke at its secret Institut für Biologische Forschung (INBIFO) in Germany."

"The number, variety, and results of the fundamental toxicological experiments done by Philip Morris at INBIFO are without parallel in the open scientific literature. These studies were neither published nor revealed to the government in... hearings by the US Occupational Safety and Health Administration."

The authors say that although exposure to secondhand smoke causes lung cancer and 53 000 deaths a year in the United States, few data exist in the open literature on the toxicology of fresh sidestream smoke.

In the study the authors, from the University of California at San Francisco, analysed research they found among 40 million pages of tobacco industry documents that were made public as a result of litigation against tobacco companies.

They say that between 1981 and 1989 the German centre did at least 115 studies of sidestream smoke. The centre's research showed that sidestream condensate caused two to six times more tumours per gram than mainstream condensate. The research also showed that inhaled fresh sidestream cigarette smoke is about four times more toxic per gram of total particulate matter than mainstream cigarette smoke.

Sidestream tar also caused two to six times more tumours per gram when painted on the skin of mice. Fresh sidestream smoke was found to inhibit normal weight gain in developing animals and, at low levels, to cause damage to the respiratory epithelium. Damage to the epithelium increased with longer exposure. The toxicity of whole sidestream smoke was found to be higher than the sum of the toxicities of its major constituents.

The authors say the research used full flavour cigarettes and may underestimate the toxicity of sidestream smoke from current cigarettes. They say evidence shows that sidestream smoke from filtered "light" cigarettes, which now constitute most of the market, is significantly more toxic than that from full flavour cigarettes.

The unpublished research supports the institution of smoke-free policies in public places, the authors say.

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Rapid Responses:

Read all Rapid Responses

Active smoker is affected more than the passive smoker

Dr.Satheesha Nayak
bmj.com, 19 Dec 2005 [Full text]

Passive smokers are severely affected

Falko Tiefenbacher
bmj.com, 19 Dec 2005 [Full text]