An estimated 40% of children worldwide are exposed to secondhand smoke (SHS) . While exposure causes serious damage to both children and adults, infants and children are especially susceptible to SHS toxicity due to their size and developmental stage . SHS exposure (SHSe) causes sudden infant death syndrome, reduced birthweight, and ottitis media, asthma, pneumonia, and impaired lung function in children . Detrimental health effects of exposure to SHS have been shown to persist into adulthood, and children with parents that smoke are known to be at a greater risk for tobacco use themselves [3, 4]. According to the World Health Organization, medical costs of children due to SHS have been estimated at $703-$897 million in the US, $239.5 million in Canada, and $267 million in Britain . Because of its potential impact, reduction of children's SHS exposure is on the agenda of major health organizations, including the World Health Organization [1, 6] and US Healthy People 2020 .
Prior approaches to reducing SHS exposure among the very young
Largely due to the difficulties of legislating bans in the private domain , little legal action has been taken to prevent the exposure of young children to SHS in the home. The use of voluntary smoking bans in the homes and cars of families with children is one possible approach. Some evidence of public support for such am approach exists in the US and elsewhere. In the summer of 2001, for example, 74% of US households had indoor smoking bans, with 84% reporting smoking bans in the presence of children ; this is corroborated by another study showing strict smoking bans in just over three quarters of US households . Support has been found not only for voluntary smoking restrictions, but also for those mandated by law. In Canada in 1996, nearly 40% of residents supported legal restrictions on home SHS child exposure . The first ban on smoking with a child in the car, enacted several years ago in Bangor, Maine , was followed by bans in other places, including Australia .
Some researchers have attempted to develop intervention programs to reduce SHSe among children, particularly in the home. These interventions have had limited success in achieving their stated goals. In a 2006 Cochrane Collaboration review of 36 trials, only 11 showed statistically significant reductions in child exposure to SHS. The review states: "Although several interventions, including parental education and counselling programmes, have been used to try to reduce children's tobacco smoke exposure, their effectiveness has not been clearly demonstrated." . The US Task Force on Community Preventive Services , in its review of community education to reduce exposure to SHS in the home, found "insufficient evidence to determine effectiveness ... because of the small number of available studies and limitations in their design and execution."
Techniques such as intensive behavioral counseling , motivational interviewing with children from low-income households , and a brief intervention with smoking mothers of newborns  have all shown some success at reducing exposure to SHS or reducing parental smoking. The potential role of pediatricians has also been highlighted , particularly because of their responsibilities in some countries to report suspected physical harm or neglect . Some interventions in the pediatric setting have shown benefit, particularly for asthmatic children . Other approaches have been found to be feasible, such as the STOP program for counseling parents in the hospital environment , or acceptable, such as physician advice for protecting children from SHS in the pediatric setting [20, 21].
Challenges related to parental perceptions and practices
Several important challenges have been identified in the literature on preventing children's exposure to SHS, in particular those associated with parental beliefs and practices regarding the impact of their own smoking on their children, or the effectiveness of the prevention measures which they employ. A central challenge is parents' denial of the detrimental effect of SHS caused by their own smoking. For example, in one study, some smoking mothers of young children, rather than admit their smoking could potentially affect their children, preferred to blame health-related issues on other factors, such as genetics or environmental pollution . Another challenge is that even when parents do recognize the potential hazard of exposure to SHS, a large percentage (over 80% in one study ) rely on simplistic "harm-reduction" strategies which they believe are effective, such as opening a window. However, research shows such strategies to be ineffective . These two types of misconceptions pose an important challenge in developing effective interventions: in addition to providing the parents with resources to adopt and maintain smoke-free environments for children, parental misconceptions regarding harm reduction must be addressed. For this purpose, a social marketing approach, which draws on behavior-change theories [25, 26] will be used to augment findings from the comprehensive literature review, by systematically identifying parents' barriers to the adoption of recommended SHS-reduction behaviors . In addition, it will use a formative evaluation strategy  to enable the development of appropriate theory-based means to address the challenges, which will avoid stigmatizing parents or making them feel guilty [29–31]. These behavior-change approaches include social cognitive theory , risk communication, the influence of social norms , and the use of various media channels (which currently include the internet and social network channels) to reach and attract the attention of the intended parent population, and to provide pertinent and persuasive information on the issue. Further, new media channels can play an important role in providing actual support and enhanced self-efficacy, which are considered to be important factors in adopting health-promoting behavior changes. Social marketing approaches also emphasize the importance of identifying subgroups (segments) within the intended population that may hold particular beliefs, have particular needs, or can be supported through particular means. This segmentation can be done on the basis of various factors, including particular "stage" of readiness to adopt the recommended behavior . Social marketing strategies have been successfully applied in the area of tobacco use prevention and cessation, and it has been recommended that they be applied in the development of current smoking prevention approaches [4, 35, 36].
Third hand smoke exposure
The concept of third-hand smoke (THS), defined as "residual tobacco smoke contamination that remains after the cigarette is extinguished," has recently surfaced as a closely related health issue. The term "tobacco smoke exposure" (TSE), is used to include exposure to both secondhand smoke and thirdhand smoke, and will be used in the remainder of this protocol .
Primary hypothesis of the current study
The primary hypothesis of the current study is that a parent-oriented theory-based intervention can reduce tobacco smoke exposure (TSE) of young children, and be evaluated in a valid manner.
The aims of the present research are to:
Develop a theory-based intervention based on a social marketing approach to reduce TSE among young children
Evaluate the effects of the intervention on TSE, as measured by biochemical measures and parental report
Evaluate the effects of the intervention on secondary endpoints: child health outcomes and parental cessation
Explore the relationship between TSE and child health
Explore the relationship between TSE as reported by parents and as measured by biochemical means.