Everything does not give you cancer, so avoid the things that might

Everything gives you cancer, or so the saying goes. But that's not what the evidence says. Of the 40,000 Australian cancer deaths in 2007, around a third were directly attributable to one or more of a handful of known risk factors: tobacco smoke; obesity and its main causes (poor nutrition and inactivity); UV radiation; excessive alcohol consumption; and occupational and environmental exposure to carcinogens (which overlaps with UV exposure).

The causes of the other two-thirds of cancer deaths in Australia remain unknown. Ageing is a key factor (cancer risk increases with age) and genetics can have an impact. Further research is required to understand what other factors, in isolation or combination, cause cancer.

It's a difficult area of study for a number of reasons. First, cancer usually occurs many years after a pattern of long-term exposure to a cancer-causing agent. Second, not everyone exposed to a carcinogen will develop cancer, for reasons we don't fully understand. Third, it can be impossible in some patients to identify which of a number of possible causes was the trigger - for example a smoker with lung cancer who was also exposed to asbestos.

The absence of a proven link between so many cancers, and the advent of the internet, has led to an increase in speculation and myth-making. Yet remarkably few previously unknown causes of cancer have been identified in the past 30 years. Where the evidence has evolved, it has built on what was already known, rather than reveal new carcinogens. (For example, alcohol was conclusively shown to cause five cancer types in 1988; another was added in 2007 following a new global analysis.)

Despite evidence showing lifestyle-related risk factors are the main known causes of cancer, there has always been a high level of community interest in the risk of exposure to chemicals - perhaps because chemicals are seen as pervasive, insidious and beyond our individual control.

Most cancer-causing chemicals were identified because of workplace exposure. Later, attention focused on whether such carcinogens could cause cancer beyond the factory gate. Asbestos mines, and steelworks using out-dated production methods (which produce coal-related pollutants - the same carcinogens in tobacco smoke, in smaller doses), were linked to cancers diagnosed in local communities as well as in the workers.

Asbestos production has been banned in Australia; other industries have cleaned up their act. But we must stay vigilant about chemical use and apply checks to help ensure workers and communities are not at risk. The time lag between exposure and diagnosis means we may not be able to establish a causative link until long after the damage has been done - as occurred with asbestos.

Apart from these industrial examples, most concerns about chemicals have not been supported by the evidence. The presence of some potentially harmful chemicals in consumer products has not translated to cancer burden, mainly because the chemicals occur in very low concentrations.

The consumer product to have generated the most cancer concern in recent years is the mobile phone, yet there is no evidence of a link from a comprehensive range of studies. (We recommend caution in children using mobile phones, as a child has greater brain elasticity than an adult, and children's use of mobiles had not been studied as comprehensively as that of adults.)

Evidence is the key to policy - health authorities can only act responsibly to prevent exposure to a possible cause of cancer if there is evidence to support the link. To do otherwise, and seek to prevent all exposure to every notified carcinogen, would make life impossible.

Media in its many forms, particularly the internet, can be a powerful and beneficial information resource. It can also spread claims that are not backed by evidence - which can be dangerous.

Research shows that people concerned by sensationalised media reports about cancer causation, or who believe that everything causes cancer, are less likely to protect themselves from the proven risk factors. So cancer scientists strive to keep the focus on what actually does cause cancer.

We need more research into causation and how we can detect cancer earlier and treat it more effectively at any stage. It's a painstaking process; filling the void with myths can be a dangerous distraction.

While our knowledge continues to grow, each of us has the capacity to avoid being one of the one-in-three Australians who will die from a lifestyle-related cancer.

World Cancer Day is 4 February 2014. This year's theme focuses on cancer myths. Cancer Council Australia has created the iheard.com.au website to make it easy for Australians to separate scientifically proven facts about cancer from misinformation, fanciful claims and myths. Visit www.iheard.com.au.