'Third-hand smoke' danger

“Parents who limit their smoking to the garden could still be harming their children,” warns The Daily Telegraph. The newspaper says this is because children can inhale toxins that remain on the clothes, hair and skin after smoking, which it terms as ‘third-hand smoke’. The story is based on a US research study.

The research behind this story did not actually assess the dangers of “third-hand” smoke, but instead surveyed people’s beliefs about these dangers, and whether this was related to the likelihood of banning smoking in their own homes.

Only 43% of non-smokers thought third-hand smoking was harmful to children, compared with 65% of non-smokers. People who believed third-hand smoke was harmful were also more likely to have a no-smoking rule in their homes. Consequently, the researchers suggest that public information on third-hand smoke might encourage home smoking bans.

Stopping smoking altogether is the best way to avoid the dangers of smoking for individuals and those around them. But if quitting smoking proves difficult, banning it in the home is a good way to protect children from the dangers of tobacco smoke.

Where did the story come from?

This research was conducted by Dr Jonathan Winickoff and colleagues from Massachusetts General Hospital and other research centres in the US.

The study was funded by the Flight Attendant Medical Research Institute, the National Cancer Institute, the Office of Rural Health Policy of the Department of Health and Human Services. It was published in the peer-reviewed medical journal Pediatrics.

What kind of scientific study was this?

This was a cross-sectional survey about adults’ beliefs about third-hand smoking, and whether these varied between smokers and non-smokers.

Third-hand smoke was defined as “residual tobacco smoke contamination that remains after the cigarette is extinguished”. This includes toxins that settle on surfaces in the home, and remain even after a cigarette has been smoked. The authors quote the US Surgeon General’s 2006 report on involuntary smoking, which concludes that there is no “safe” level of exposure to tobacco smoke.

The researchers say that “the majority of adults are aware that visible [second-hand smoke] is harmful to health” and that some smokers take measures to avoid exposing others, for example by avoiding smoking around non-smokers in the home.

The researchers believe that people who were aware of the dangers of third-hand smoke would be more likely to ban smoking inside their own homes.

These results come from the 2005 Social Climate Survey of Tobacco Control, which is an annual nationwide telephone survey. Computer programmes randomly selected a nationally representative sample of telephone numbers to dial. Researchers asked to speak with the adult in the home whose next birthday was nearest to the time of the phone call. The person was then asked if they would take part in the survey.

Those who agreed were asked questions about whether they currently smoked (defined as having smoked 100 cigarettes or more in their lifetime, and now smoking every day or some days). They were also asked what smoking policy they maintained in their homes, e.g. was smoking allowed in the whole house, part of the house, none of the house, or were the respondents unsure or unaware of the policy.

Other questions assessed how strongly the telephone respondents agreed or disagreed with two statements about second and third-hand smoke:

• “Inhaling smoke from a parent’s cigarette can harm health of infants and children”
• “Breathing air in a room today where people smoked yesterday can harm health of infants and children”. 
  Participants were also asked whether they knew about smoking policies in local restaurants and bars.

The researchers then looked at what proportion of people believed that second and third-hand smoke was harmful. They also looked at whether this varied among smokers and non-smokers, those with different home smoking policies, and different levels of knowledge about smoking policies in local restaurants and bars.

The results also took into account factors that might also affect the results, such as educational achievement and race.

What were the results of the study?

1,478 adults completed the survey, and almost a fifth of these people were current smokers. About one quarter of participants lived in a house with a smoker.

The majority of participants (93%) believed that second-hand smoke was harmful to children, but only 61% believed that third-hand smoke was harmful. About a fifth of people reported that they did not know if third-hand smoke was harmful for children, compared with only about 3% not knowing if second-hand smoke was harmful.

A strict smoking ban in the home was more common among non-smokers (88%) than among smokers (27%). People with a strict home smoking ban were more than twice as likely to report that third-hand smoking was harmful than those who did not have such a ban.

What interpretations did the researchers draw from these results?

The authors concluded that there is an association between the belief that third-hand smoke is dangerous and strict home smoking bans. They suggest that “emphasising that third-hand smoke harms the health of children may be an important element in encouraging home smoking bans”.

What does the NHS Knowledge Service make of this study?

This large survey highlights the fact that a considerable proportion of people are not aware of the dangers of lingering toxins from cigarette smoke. There are some points to note when interpreting this research:

• The survey was taken in 2005, and beliefs may have changed since then. Also, the survey was carried out in the US and may not be representative of beliefs in other parts of the world.
• The degree of danger caused by “third-hand smoke” was not assessed in this study.
• Because the study was cross-sectional and did not ask about people’s motivation for home smoking bans, it cannot prove that their third-hand smoke beliefs caused them to ban smoking in their homes. However, it makes sense that these beliefs, among others, might influence a decision about whether to allow smoking in the home.
• The study does not assess whether education about the harms of third hand smoke will affect smoking in the home or smoking rates in general. Further research will be needed to determine if this is the case.

Contrary to The Daily Telegraph’s message (which highlights the dangers of smoking even outside the house), the main conclusion of the authors of this paper is that knowledge about the dangers of third-hand smoke is associated with home smoking bans. They say that informing people about the dangers may motivate them to take the positive step of having a smoking ban in their homes.

The authors acknowledge that toxins may still be found on clothes, or enter via windows and doors, and that a smoking ban at home should ideally be accompanied by efforts to stop smoking altogether.