Human lungs are created to breathe clean air: the questionable quantification of vaping safety "95% less harmful"

The New Zealand government is aiming for Smokefree Aotorea, equivalent to a reduction in smoking prevalence to 5% or less by 2025. E-cigarettes may be one tool to meet this target, but how safe are they? Little is known about their long-term health implications in humans. In 2015, Public Health England commissioned a report summarising the available literature on e-cigarettes and coined the now well-known quantification that "e-cigarettes are 95% less harmful to your health than normal cigarettes". In this article, we argue that this is an unfounded quantification because the data required to make this quantification are not yet available. The value of '95% safer' was based on a study estimating the relative harms of nicotine-containing products that utilised scoring from a selected panel of experts. One of the key limitations of this quantification is that while the scores provided by the panellists were informed by knowledge, they are fundamentally value judgements and are not an exact science. E-cigarettes are probably safer than conventional cigarettes, however, there is mounting evidence that they are not without harm and the long-term health impacts are not yet known.