Passive smoking: is there convincing evidence that it's harmful?

Last year, the Health Secretary Patricia Hewitt declared that a ban on smoking in public places "will save thousands of lives". Official estimates assert that 12,000 people a year die in Britain from the effects of passive smoking. In Scotland, a ban on smoking in all public places began in March, following a lead set by the Irish government. The Welsh Assembly is preparing to follow suit. In England, smoking will be banned in pubs, clubs and restaurants from the summer of 2007.

But none of these restrictions is based on convincing proof that passive smoking kills. It is an assertion that owes a great deal to the sanctimonious superstition that there can be no smoke without death. Reputable scientists admit this. On Desert Island Discs in 2001, Sir Richard Doll, the man who proved the incontrovertible causal link between active smoking and lung cancer, said: "The effect of other people smoking in my presence is so small it doesn't worry me."

He was right not to fret. One of the largest studies of the health consequences of secondary smoking was published in the British Medical Journal in 2003. It tracked the health of 118,000 Californians over four decades in a rigorous attempt to identify a causal relationship between environmental tobacco smoke (the scientific term for secondary smoke) and premature death. It concluded: "The results do not support a causal relationship between ETS and tobacco-related mortality."

That caused a nasty row. Anti-smoking campaigners condemned the research as "biased" and "unreliable". The anti-smoking charity Action on Smoking and Health (Ash) declared. "This could be very damaging as it will be used by industry lobbyists to argue against laws to ban smoking in public places and workplaces." And Ash was not alone in being concerned about the threat posed to its ambitions by scientific honesty. The venerable BMJ found itself under attack from all sides.

Publication provoked a barrage of condemnation in which the then BMJ editor Dr Richard Smith was accused of every failing from naivety to active promotion of evil. His accusers demanded that he withdraw the article. To his credit, Smith refused, pointing out that the BMJ exists to publish science not polemic, and that the American study was proper, peer-reviewed science. A robust and persuasive anti-smoker, he replied that although the BMJ was "passionately anti-tobacco" it was not "anti-science". He went on to explain that "the question [of whether passive smoking kills] has not been definitively answered."

Doctors and scientists who make such statements come under extraordinary pressure to withdraw them. Three years later, Dr Smith appeared to be satisfied that passive smoking does kill. Doll was persuaded to emphasise that his lack of concern about secondary smoking was a purely personal perspective. The tragedy, for those who care about truth, reason and scientific method, is that it was not. Profound scepticism about the claim that secondary smoking kills is the only rationally tenable position. Look beyond the lazy political and media consensus that simply assumes that because smoking kills secondary smoking must as well, and the evidence is overwhelming.

When I interviewed her in 2004, Amanda Sandford of Ash acknowledged unintentionally that much secondary smoking science is unscientific. She said: "A lot of the studies that have been done on passive smoking produce results that are not statistically significant according to conventional analysis." In plain English, that means that if secondary smoking were not already the focus of a torrent of moral sanctimony, few reputable scientists would dare to assert that it causes lung cancer, heart disease or any of the other life-threatening conditions with which it is routinely associated.

Dr Ken Denson, a medical professional who is prepared say what others only think, puts it more bluntly: "The ill effects of passive smoking are still intuition rather than scientific fact... All in all, the medical evidence for any deleterious effect of passive smoking is extremely tenuous and it is unlikely that it would ever stand up in a court of law."

A recent report by the International Agency for Research on Cancer reveals that, "In total, 23 studies have been published on [workplace] exposure to secondhand smoke. Only one reported a statistically significant association between exposure to secondhand smoke at the workplace and risk for lung cancer." One out of 23 is usually dismissed as a rogue result.

Since then, further evidence has been published by the BMJ. In March 2005 it offered fresh data suggesting that passive smoking may kill 11,000 people a year in the UK. The crucial word is "may". If there is a direct causal link between secondary smoking and lung cancer it is so tiny that dedicated campaigners have struggled to identify it. Scotland's Green Party, hardly a promoter of smoking, recently alleged that more Scots are killed by exhaust fumes than by secondary smoke.

Of course secondary smoke can be irritating. Some people detest the smell; others believe it exacerbates their asthma - a claim for which there is some evidence, although it is noteworthy that the incidence of asthma in the UK has risen sharply during a period when the level of smoking has fallen. Nor is it a good idea to expose very small children to dense cigarette smoke.

But the best summary of the passive smoking debate was provided by Dr Smith at the time of the 2003 BMJ controversy. He said: "I found it disturbing that so many people and organisations referred to the flaws in the study without specifying what they were. Indeed, this debate was much more remarkable for its passion than its precision." That goes for every claim advanced by politicians, charities and health campaigners who demand a smoke-free environment and consider it legitimate to deny freedom to smokers by pretending that their habit harms non-smokers.

Reputable research shows that a non-smoker inhales between a 500th and 1,000th of the toxins inhaled by the smoker himself. No matter what poor Roy Castle believed about the effects of years in smoky jazz clubs, there is little scientific proof that secondary smoke causes cancer. And, if very little increased risk can be demonstrated for lung cancer, it is beyond improbable that an increased risk can be proven for other smoking-related diseases where the risks for the active smoker are much lower than for cancer.

The logic is that distortions paraded in a good cause are virtuous. But, a non-smoker myself, I find it alarming that the Government is prepared to base legislation on what is barely more than superstition. Smoking only kills you if you stick the cigarette in your own mouth. To pretend otherwise is mumbo-jumbo.

Those who disagree should remember a lesson from the history of anti-smoking. Doll's post-war study was not the first to prove that smoking caused lung cancer: Nazi scientists had reached the same conclusion 20 years earlier. The resulting evidence was ignored in this country because it came from a tainted source. It was assumed that good science could not come from an evil regime. In the modern-day debate over secondary smoking, campaigners who pretend there is proof that it kills are repeating that historic error in reverse. Excellent motives are producing grotesquely distorted science.

USA

California pioneered the public smoking ban in 1993 and has some of the toughest laws. Other states and territories have followed suit, but legislation varies

Cuba

Smoking is banned in offices, shops, theatres, buses, taxis, schools, sports facilities and air-conditioned public areas.

Italy and Sweden

Restaurants and bars are smoke-free

Spain

Offices, hospitals etc 100 per cent smoke-free. Small businesses can choose, but must declare their smoking status

Africa

Limited restrictions in Eritrea, Uganda and South Africa

Iran

No smoking in most enclosed public spaces. But the ban is largely ignored.

Australia

Most provinces smoke-free or with legislation pending