As Germany plans to ban smoking in cars with children or pregnant women, the German newspaper, Die Zeit, asked experts to weigh in on the forthcoming policy. The experts concluded that this policy does not go far enough and advised caution, especially for children, due to long-term risks posed by thirdhand smoke exposure (known as cold smoke exposure in Germany). Read the full story to answer the question, “Does Cold Smoke Make You Sick?”

Cold Smoke
Does cold smoke make you sick?

In rental cars, at the cinema, and on the neonatal ward: remnants of tobacco smoke can be found almost everywhere, even where smoking has never occurred. The extent of this phenomenon is only now becoming apparent.

By Claudia Wüstenhagen
July 17, 2023

Hardly stepping into a car and taking one breath, it becomes clear: Someone has smoked in this car! This should not happen, as smoking is usually prohibited in car-sharing vehicles. Nevertheless, one occasionally encounters such a stinking car. It’s disgusting, no doubt. But is it also unhealthy? Can you safely go on a family vacation in such a car?

Recently, it was announced that German Health Minister Karl Lauterbach (SPD) plans to ban smoking in cars where children or pregnant women are passengers. Many experts consider such a rule long overdue, as smoking in cars can quickly lead to pollutant concentrations comparable to those in a smoky bar. And today, almost everyone knows that secondhand smoke is harmful.

Less known, however, is that medical professionals are also concerned about the toxins that remain after smoking. They adhere to the skin, hair, and clothing or persistently settle in indoor spaces, lasting for weeks, months, or even years in dust and on surfaces, in furniture and mattresses, books, and curtains. And yes, even in car seats.

Experts refer to this as cold smoke or thirdhand smoke – analogous to secondhand smoke from passive smoking. Cold smoke has only been studied for a few years, but experts are increasingly warning about the potential risks it may pose.

Carcinogenic substances

In a recent analysis published in the journal Tobacco Control, US researchers explain why they are concerned: A total of 26 substances classified as carcinogenic, harmful to fertility, or causing deformities in children were detected in deposited cigarette smoke (Matt et al., 2023). These substances include benzene, benzo(a)pyrene, formaldehyde, and certain heavy metals such as cadmium. In addition, there is nicotine – which does not itself cause cancer but can react with substances in the environment and produce harmful substances.

“These toxins from cold smoke can enter the body,” says Katrin Schaller, a biologist and tobacco prevention expert at the German Cancer Research Center (DKFZ) in Heidelberg. Because what hangs in dust, upholstery, or carpets can be whirled back into the air – and thus enter the respiratory tract. And what sticks to surfaces, objects, or even toys quickly ends up in the mouths of small children. Schaller also says that the body can absorb such toxins through the skin.

Almost no place is free of contamination

This is alarming because cold smoke surprisingly lingers for a long time and reaches places where one would not necessarily expect it. Researchers from the Max Planck Institute for Chemistry found traces of deposited tobacco substances in a cinema in Mainz, despite a strict smoking ban for 15 years. Apparently, cinema-goers brought in old smoke anew each time. Those who watched a movie there at the time of the measurement received approximately the same dose of toxins as someone who passively smokes one to ten cigarettes (Science Advances: Sheu et al., 2020).

For Georg Matt, the measurements from the Mainz cinema were not surprising. “The toxic legacy of tobacco smoking affects us all, as there are very few indoor spaces that are safe from these chemical residues,” he says. Georg Matt is one of the most meticulous researchers in the world in this field, heading the Thirdhand Smoke Resource Center at San Diego State University and being part of a research consortium warning about the consequences of cold smoke. “The harm caused by tobacco consumption goes far beyond the diseases and deaths among smokers and passive smokers,” says Matt. “It is time for society to finally do something about it.”

Matt is, in a sense, a kind of human smoke detector – for long-extinguished cigarettes. His team showed years ago that the apartments of former smokers were still contaminated with toxins even months after they had quit smoking. Even non-smokers who moved into former smokers’ apartments showed traces of nicotine on their fingers and in their urine.

On another occasion, Matt demonstrated that even hotel rooms for non-smokers contain cold smoke, just like supposedly smoke-free rental cars. However, what shocked many the most was when Matt and his colleagues found smoke residues in places where smoking had certainly never occurred and should never occur: in a neonatal intensive care unit.

Cell damage and altered immune system: How significant is the risk?

In a small study, the researchers examined the hospital rooms of babies whose mothers were smokers. Swabs of smoke deposits on chairs, baby cribs, and incubators tested positive. Additionally, cotinine, a breakdown product of nicotine, was found in the urine of newborns. A larger follow-up study confirmed the findings – and revealed even more. This time, nicotine samples were positive in the hospital room furniture and urine of babies whose parents were non-smokers (Nicotine & Tobacco Research: Northrup et al., 2021).

“It is highly likely that visitors and clinic staff carried these substances into this sensitive environment, either on their clothes, skin, and hair or through their breath if they were smokers,” says Matt. Indeed, there were generally more residues found in the hospital rooms when the babies received a lot of visitors.

Do people get sick from Thirdhand Smoke?

“Our studies show that the harms of tobacco use are underestimated,” says Matt, as thirdhand smoke is often overlooked as a toxic substance indoors. In the published study on cold smoke in the neonatal ward, he and his colleagues warn about the possible consequences, especially for premature babies who are particularly vulnerable, as their skin is still underdeveloped and may be more easily exposed to toxins.

Whether contact with these substances actually harms the health of babies and adults – acutely or in the long term – is still unclear. And this is precisely a general problem with the current state of research on thirdhand smoke: As shocking as some findings may be, they cannot definitively determine how dangerous the pollutant exposure actually is.

Do people really get sick from thirdhand smoke? And if so, at what dosage? “We don’t know all of that for sure yet,” says Katrin Schaller from the DKFZ. While the negative effects of secondhand smoke – such as lung cancer or stroke – are well-established, there is less robust data on the effects of thirdhand smoke, particularly the lack of long-term studies in humans. Even Georg Matt admits, “The exact additional risk attributable to thirdhand smoke is a puzzle that we still need to put together.”

However, there are some initial indications – pieces of this puzzle: “Laboratory tests on cells show that thirdhand smoke can damage cells and genetic material,” says biologist Schaller. Animal experiments have also shown that cold smoke increases the risk of lung cancer and alters the immune system, and wound healing is affected. In human test subjects who inhaled cold smoke briefly, acute changes occurred in the cells of the nasal mucosa, including increased DNA repair, which can be interpreted as a direct response to genetic damage.

“From these studies, it is clear that processes can occur in the body that are not beneficial to health,” says Schaller. However, to determine the real long-term effects, one would need to scientifically follow as many people as possible exposed to cold smoke in everyday life for years. And during this research, it would be necessary to ensure that the negative effects are truly caused by cold smoke and not by other factors like passive smoking, which these individuals are often exposed to as well.

According to current knowledge, Schaller says, health damage from thirdhand smoke – with long-term and high exposure – cannot be ruled out. However, the extent to which the risk of diseases increases and the necessary quantities for this to happen cannot be determined based on the available data. Most likely, the exposure to cold smoke is significantly lower than that of passive smoking or active smoking.

The phrase “with long-term and high exposure” also shows that it’s probably not the one-time ride in a smoky rental car that should be a concern. Schaller wants to avoid spreading panic on this topic. Often enough, frightened parents call her at the DKFZ because they moved into a former smoker’s apartment with their children. Schaller says she tries to reassure them first.

However, she advises callers to remove both carpets and wallpapers from the apartment and to clean window and door frames thoroughly, especially at the beginning. “Replace what is replaceable,” says Schaller. That way, most of the contamination is already eliminated. “One should take the research findings seriously and avoid cold smoke as much as possible.”

Why smokers should never return directly to the house

In general, smoking should only be done outside, never indoors. And those who extinguish their cigarette in front of the house should not immediately go back inside, according to the DKFZ in a fact sheet. This is because smokers continue to exhale carcinogenic benzene and other toxic substances up to ten minutes after smoking a cigarette.

Why children are particularly at risk – and how to protect them

Children are generally considered particularly vulnerable to thirdhand smoke – as they are with environmental pollutants. This is because they breathe in and out more often than adults, because they pick up more dust while crawling or playing on the floor, and because they explore the world with their mouths – licking their fingers and objects on which pollutants may stick. Moreover, children have worse detoxification systems than adults, says Schaller. As the child’s body is not yet fully developed, it may not be as efficient at neutralizing or getting rid of toxins.

For this reason, both the DKFZ and the American Thirdhand Smoke Resource Center recommend not smoking before being in contact with children. And if you cannot or do not want to give up smoking, at least change your clothes and thoroughly wash your hands. In their extensive FAQ, the US researchers even suggest showering before contact with children.

When buying a car, experts recommend checking whether the previous owners were smokers, as it is “almost impossible” to rid cars of cold smoke. And it is best not to get into a smoke-filled car with children – or at least adjust the ventilation to let fresh air from the outside flow in. A towel under the child’s seat can also serve as a barrier to minimize the amount of toxins the child’s car seat absorbs. After the ride, parents should wash their child’s hands and face.

Reading the comprehensive list of recommendations from US researchers may make one feel uneasy. Therefore, it is important to emphasize: The actual need for all these precautions has not been scientifically proven yet.

What responsibility does politics bear?

For Katrin Schaller and Georg Matt, the current findings are an argument for tightening regulations on protecting non-smokers. For example, there should be no exceptions to smoking bans in indoor spaces – so no smoking areas in restaurants either. And at least in state-owned social housing, the government could consider a smoking ban.

If it were up to Georg Matt, politics should also take responsibility for testing spaces for thirdhand smoke, thoroughly cleaning apartments and other buildings of smoke residues – and billing the significant costs to the tobacco industry.

Consistently, Health Minister Karl Lauterbach should completely ban smoking in cars, not just when children and pregnant women are present. The chances for this are likely slim, as his current proposal is already heavily criticized. The Free Democratic Party accuses him of “health obsession.”

Note: Content was edited for style and length.

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