Can environmental cigarette smoke cause lung cancer?

A cigarette emits two types of smoke. The smoker himself/herself is exposed to mainstream smoke pouring down into the lungs. Between the puffs, the cigarette smoulders, and emits so-called side stream smoke. Due to the lower temperature, this type of smoke may contain higher quantities of dangerous compounds than the mainstream smoke. Therefore the risks may still be significant even though the smoke is more dilute.

Personal smoking

There is a huge amount of information on active smoking. One of the most comprehensive studies is a cohort of 35,000 British medical doctors which has been going on for over 50 years. Tobacco smoking contributes to the death of every other smoker, or perhaps for even two out of three. Male smokers die on average 10 years younger than non-smokers. This does not exclude the possibility that the occasional smoker may live to the grand old age of 90 years or more. Stopping smoking at the age of 50 will halve the extra risk, so it is worthwhile stopping at any time. Mortality is double in all age groups of male smokers from early middle age onwards. There is not as long and as comprehensive data on women but there is no reason to suspect that they would fare better than their male counterparts.

Risk is highly dependent on the number of years an individual has been a smoker, so starting to smoke during adolescence is especially dangerous. The excess mortality is caused most of all by cardiovascular diseases, various cancers and respiratory diseases. The risk of lung cancer is the highest, the probability of lung cancer is on average 16-fold as compared with non-smokers. The total number of deaths from cardiovascular diseases due to smoking is larger, however, because the overall mortality from cardiovascular diseases is larger in the total population.

Smoking during pregnancy results in the birth of a 200 g smaller baby (150–400 g depending on the number of cigarettes per day) and is responsible for about 15% of premature births. It may also contribute to cancer risk in the child. One fallacy to be corrected – so called “light” cigarettes are no safer than conventional cigarettes, because the smoker unconsciously “corrects” the puff characteristics to obtain the sought after taste and nicotine dose.

Environmental tobacco smoke

Individuals are exposed to varying amounts of environmental tobacco smoke (so called passive smoking) e.g. depending on their occupation or whether they live in the same household as a smoker. Passive smoking has been estimated to cause an average increase of 20% in the lung cancer risk (in other words 1.2-fold risk while personal smoking causes a 16-fold increase). In 2004 The International Agency for Cancer Research (IARC) of the World Health Organisation classified environmental tobacco smoke as a definite human carcinogen.

All tobacco smoke, also environmental tobacco smoke, contains up to 4,000 chemicals, and at least 50 of them are certain, probable or possible carcinogenic substances. There is much less evidence of the risk of other cancers than lung cancer, but because personal smoking is known to cause a number of different cancers, it is likely that environmental tobacco smoke also increases the risk of other cancers. The number of cancers due to environmental tobacco smoke may vary between 1 and 10% of those caused by personal smoking, depending on tobacco policies. In many countries, smoking in public places has been restricted or banned, and this would be expected have a clear impact on the cancer risk.

Other important effects are increased risk of cardiovascular diseases, and increased respiratory diseases in children. As an example of the relative importance, in Finland with a population of 5 million, almost 2000 active smokers die from lung cancer per year, and passive smoking is estimated to cause 700 deaths from heart diseases and 100 deaths from lung cancer.

The increased risk of children's infectious diseases has been well documented. Most of these infections occur in the respiratory tract and middle ear; in some studies children who live in the same house as a smoker have a many times greater risk of suffering these infections. Even children's asthma is believed to increase, and it is clear that the symptoms of existing asthma are worsened. Exposure to environmental tobacco smoke has even been suspected of causing low birth weight and increasing the risk of developmental defects in the baby.

Similarly to personal smoking also environmental tobacco smoke increases lung cancer – this can be stated with certainty, and it probably elevates the risk of many other cancers. It also increases cardiovascular mortality. Tobacco smoke kills more people than any other chemical.

One level up: The air that we breathe

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