Public Health England’s use of smoking as a benchmark for the relative safety of vaping (Public Health England maintains vaping is 95% safer than smoking, 28 December) will puzzle many given that smoking is not, by any reckoning, “safe”. The key research finding, described in their own report in terms of estimated relative harms, is that the harm to vapers is around 5% of the harm to smokers. The “95% safer” figure arises because 100-5 = 95. However, this formulation is not intuitive; the use of “95% safer” risks confusion. Some assume it means that vaping is 95% as harmful as smoking; others that you are 95% more likely to suffer harm from smoking compared with vaping. Both interpretations hugely understate the relative harm of smoking compared to vaping; few people correctly appreciate that smoking is 20 times more harmful than vaping. Public health depends on the public understanding of risks – reporting that vaping is 5% (or 1/20th) as harmful as smoking is less ambiguous and acknowledges risk.

Professor Peter Ayton

City, University of London

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