Vaping clearly carries risks. Starting in 2019, America’s Centres for Disease Control and Prevention (CDC) began to track a new inflammatory respiratory disease known as EVALI (“e-cigarette or vaping product use-associated lung injury”). As of February 18th 2020, the CDC had identified 2,807 admissions to hospital for EVALI in America. At least 68 of those patients had died.

Swift action ensued. Researchers pointed fingers at vitamin E acetate, a skincare oil that was added to many illicit batches of vaping liquids as a thickening agent. When vitamin E acetate is vaporised by a vape’s heating coil, highly toxic ketene gas is produced. Many jurisdictions outlawed any addition of vitamin E acetate to vape liquids, and crackdowns on black markets followed. EVALI cases fell sharply, and the CDC has not detected a resurgence.

Yet health authorities believe EVALI might also be caused by other substances in vape aerosols, including those that are manufactured legally. In a landmark analysis of four popular vaping liquids published in Chemical Research in Toxicology in 2021, a team at Johns Hopkins University labelled six ingredients—including caffeine and tributylphosphine oxide, a pesticide precursor—as potentially hazardous. Earlier studies had found vaping mixtures that used formaldehyde, as well as heavy metals such as chromium and lead.

There are other reasons to be concerned. First, as vaping only surged in popularity in the past dozen or so years, cancer cases could still crop up. Lab mice, which can develop diseases quickly owing to their fast metabolisms, have developed cancers after being subjected to vape aerosols. The second is that vape aerosols have been found to damage human tissue, including DNA, via a process called oxidative stress.

This sounds grim. Yet researchers mostly concur that vaping is less harmful than smoking. Of the more than 7,000 substances generated by burning tobacco, over 70 have been linked to cancer, and a greater number are toxic. Vape aerosols share some of those carcinogens and toxins, but generally at much lower levels. Crucially, vaping delivers no carbon monoxide or tar, two of the biggest nasties in cigarette smoke. A review of 39 studies that was published in January in Tobacco Induced Diseases found “no significant incident or prevalent risk” of cancer in vapers who had never smoked.

What is more, taking up vaping, which mimics smoking gestures, seems to make the latter habit easier to kick. Consider a study of 886 British smokers published in the New England Journal of Medicine in 2019. All wanted to stop smoking. Roughly half were given nicotine via patches, gum, mouth spray and the like. The rest were given nicotine vapes. A year on, 9.9% of the first group had quit smoking. The figure for those given vaping kits was 18%. And among participants still smoking, the vapers had been lighting fewer cigarettes.