Commentary: What’s the science behind Singapore’s policy on vapes?
Toxicology has given us an objective way to appraise the health risks of e-cigarettes, says NUS Associate Professor Ho Han Kiat.

Stickers at a Singapore coffee shop warning about the penalties for vaping.
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SINGAPORE: Since its implementation in 2018, there has been debate about the effectiveness of Singapore’s ban on vapes, and if more must be done to deter youths from vaping.
The Health Sciences Authority on May 8 said that it is reviewing penalties to tackle the advertising, importation and distribution of vapes, and highlighted efforts to promote “pro-health” content, such as a vape-free campaign targeted at youths.
Singapore is among 39 countries worldwide that have banned vapes, in contrast to 82 countries that regulate the sale and distribution of e-cigarettes.
In discussions surrounding Singapore’s vaping ban, some have questioned if this approach is overly cautious. Countries such as New Zealand and the United Kingdom take the stance that vaping poses fewer harms than smoking cigarettes and can help smokers quit.
Here are toxicological insights that can address a few pertinent questions.
KNOWN HAZARDOUS SUBSTANCES IN VAPES
Much like conventional cigarettes, e-cigarettes contain thousands of chemicals. There are several well-established classes of hazardous substances in vapes, including heavy metals, polyaromatic hydrocarbons (found in coal and fossil fuels) and fine particulate matter.
Heavy metals such as arsenic, cadmium and chromium are linked to cancer. Cadmium, found commonly in batteries, can damage the airway, resulting in respiratory difficulty.
Polyaromatic hydrocarbons belong in one of the best studied groups of substances that we call procarcinogens. Procarcinogens don't harm us immediately at the point of inhalation, but can be metabolised by our bodies and converted into carcinogens, which are substances that can cause cancer.
Fine particulate matter, when inhaled, can travel all the way into the lungs’ air sacs where gas exchange takes place.
What this means is that every puff on a vape - just like every puff on a cigarette - transports substances into your body that could cause health problems.
As these particles are difficult for the body to break down, their presence triggers a continuous but futile response from the body to get rid of them. This can result in excessive phlegm production, and chronic inflammation of the respiratory tract.EXPOSURE TO HARMFUL CHEMICALS WHEN VAPING
But do these harmful substances in vape products always lead to health problems?
One of the founding principles in toxicology is that every drug is a poison, and it is the dose that makes it. To determine if something is toxic, we need to consider how much of it we're exposed to and for how long. The higher the dose and the longer the exposure, the worse it gets.
While vapes contain the same harmful chemicals found in conventional cigarettes, how does exposure to these substances differ?
This is a difficult question to answer because the composition and proportion of each substance may differ across vape brands and manufacturers, and how frequently a user vapes. Nonetheless, we can arrive at a reasonable estimate if we use a specific ingredient as a point of reference: Nicotine.
An average 2ml vape pod with 20mg of nicotine contains as much nicotine content as 20 to 40 cigarette sticks. If a heavy vaper goes through a pod a day, it is certainly not an insignificant amount to be dismissed.
ADDITIONAL HEALTH RISKS OF VAPES
So far, we have estimated the risk of harm by comparing with cigarettes, assuming that the hazardous substances in e-cigarettes are largely the same as in conventional cigarettes.
However, vapes may have other toxic chemicals that conventional cigarettes don't.
For example, e-cigarettes use substances like propylene glycol to create vapour.
While propylene glycol is generally regarded as safe for use at certain levels in food and medicines, we don’t know if it’s safe to breathe in for a long time. Some people have had rare but serious allergic reactions to propylene glycol.
Vapes also produce substances from their heating elements that regular cigarettes don’t.
Formaldehyde, a chemical used to preserve dead bodies, can be generated through the intense burning and oxidation of volatile substances in vape juice. Breathing in formaldehyde can damage the cells in your respiratory tract.
Finally, vapes have flavouring agents such as vanillin, menthol and diacetyl to make them more enticing to the users. Diacetyl in particular is especially dangerous, and can cause "popcorn lung", a crippling condition known since the early 2000s.
This namesake arose from reports of US popcorn factory workers who came down with acute damage to their airways, caused by diacetyl being added into microwave popcorn to give it a buttery flavour. The damage was severe and permanent, requiring lung transplant.
Even if the flavouring agents themselves are not harmful, they can make vaping more enjoyable, leading people to vape more. Inadvertently, this exposes the user to a higher dose of other noxious substances of greater concern.
RISK OF ADDICTION WITH VAPING
Nicotine is the main ingredient in cigarettes that makes people addicted to smoking. Its presence in vape products can cause dependency in e-cigarette users as well.
Addictive substances like nicotine bind to receptors in the brain that stimulate a pleasure response, for instance dopamine release. This effect is stronger in younger brains that are still developing.
It is worth noting that besides nicotine, cigarettes contain other psychoactive components such as nornicotine, anabasine and acetaldehyde.
A study by the US Food and Drug Administration detected anabasine in several e-cigarette products. Separately, acetaldehyde is a known carcinogen and can be generated under high temperatures as a by-product of several volatile chemicals.
Toxicology has given us an objective way to appraise the health risks of e-cigarettes. There is no lack of scientific basis that vapes carry similar hazardous substances as conventional cigarettes; expose users to additional although unvalidated risks; and possess the same ingredients that cause addiction.
But the question of whether public policy on vaping controls is within the Goldilocks zone has to be interrogated by the government, businesses and members of the public.
Public policy must also be counter-balanced with individual responsibility. The more individuals take personal and social responsibility, the less we need to rely on public policy as guardrails. Accurate knowledge can steer us towards making responsible choices.
Ho Han Kiat is Associate Professor at the Department of Pharmacy and Pharmaceutical Sciences, Faculty of Science, National University of Singapore.