Third-Hand Smoke and Public Transportation: Are Passengers At Risk?

Most people know about the dangers of second-hand smoke, but do the risks of tobacco stop there? The phenomenon of third-hand smoke means people could be at risk even when nobody actually smokes near them, and is particularly relevant to public transport.

The risks of smoking are becoming increasingly widely-known in society, but there are new issues like third-hand smoke which still haven’t broken through into the public consciousness. The risks of third-hand smoke and public transportation, in particular, could be important for non-smokers and especially children who are exposed, but the science on the potential risks is currently in its infancy. Finding out what we know about third-hand smoke, whether there is a risk to bystanders and who is most likely to be at risk is essential if you want to minimize your risk.

What is Third-Hand Smoke?

Third-hand smoke refers to what happens well after somebody has smoked. Although the physical smoke seems to disappear, small amounts of smoke residue settles on surfaces and clothing, and remains there long after smoking has finished.

This residue contains nicotine, although the levels are pretty low – with studies showing a maximum of about 0.073 mg per square meter – and this nicotine can react with common constituents in the air to produce carcinogenic compounds. Again, the levels of these chemicals are low, but any exposure to carcinogens carries some risk.

The concern is that these reaction products can form and then be released back into the air long after smoking has finished. So this means the air in a room where somebody has been smoking – even hours or days after the smoking actually happened – could still be contaminated with chemicals from cigarettes.

Are There Risks to Third-Hand Smoke Exposure?

To date, there are no studies demonstrating a real-world risk from exposure to third-hand smoke. The research that has been done shows that chemicals from smoke are deposited onto surfaces, and can react with common components of air to form carcinogenic chemicals. Other studies use animal models to investigate the mechanisms through which third-hand smoke could cause harm.

The evidence so far does show that there is potential for third-hand smoke to harm people in a room with somebody who has smoked or where somebody has smoked before, but the actual level of risk from third-hand smoke is unknown. However, the low levels of harmful chemicals in third-hand smoke mean that any risk that exists will probably be very small. For example, although second-hand smoke is a significant source of risk for a non-smoker, the risks are much smaller than the risks for the active smoker. The risks of third-hand smoke would be expected to be smaller still.

Who is Most at Risk of Third-Hand Smoke Exposure?

Considering who would be at greatest risk from the association between third-hand smoke and public transportation is important for anybody concerned. Although – as stressed in the previous section – the risk is more hypothetical than definitively established, babies and small children would be at the greatest risk from third-hand smoke exposure.

As Professor Michael Siegel from the Boston University School of Public Health points out, though, the much greater exposure from second-hand smoke should be the main concern. While third-hand smoke could theoretically pose a risk, if somebody is exposed to second-hand smoke, this would be the main concern for their health by a substantial margin. In other words, minimizing your children’s exposure to third-hand smoke is a good idea, but the main concern should be second-hand smoke.

Third Hand Smoke and Public Transportation

For the issue of third-hand smoke and public transportation, the potential risk is unfortunately hard to avoid. The good news is that smoking on public transport is a thing of the past, but there is nothing that can be done to prevent a smoker from lighting up outside while waiting for a bus and then getting on board. The smoke you can smell on people’s clothes after they’ve had a cigarette is effectively third-hand smoke being released, and really there is nothing you can do to stop it.

This leaves two possible solutions: minimize your children’s exposure to third-hand smoke by limiting journeys on public transportation, or to keep the focus on avoiding second-hand smoke and try to remember that third-hand smoke is a less serious concern. This isn’t ideal – because third-hand smoke probably does pose some risk – but it allows you to focus on the main source of risk rather than worrying about something that can’t be prevented, especially if you need public transportation to get through your day-to-day life.

Avoid Smoking and Second-Hand Smoke First, and Third-Hand Smoke if Possible

The risks of third-hand smoke are yet to be quantified, and are likely to be fairly small in comparison to second-hand and (especially) first-hand smoking. Some risks are likely to exist, but they’re so hard to completely avoid – for yourself or your children – the best thing to do is focus on the larger-risks from second-hand smoke exposure. To prevent third-hand smoke exposure entirely, we would have to eradicate smoking from society, which is a goal we wholeheartedly support. However, it’s challenging to accomplish, and will likely take some time to be achieved. In the meantime, if you smoke, you should quit, and encourage anybody spending time around your children to do the same.