While smoking and exposure to second-hand tobacco smoke (SHS) in most public places is addressed by smoke-free regulations, the exposure to SHS at private places, such as homes, is still prevalent in Spain and represents a significant public health challenge.

Main objective of the study: to evaluate the effectiveness of an evidence-based intervention to create smoke-free homes in households with children.

Design: cluster randomised controlled trial. Target population: families with children (≤18 years old) and at least one smoker who allow smoking in the home.

Sample: 51 clusters per group (intervention and control) with an average 4 participants per cluster. In total, 102 schools and 408 participants.

Recruitment: The Tobacco Control Unit, the study promoter, will invite the Associations of the Students' Families (ASF) of schools in the Metropolitan Area of Barcelona to join the study. Those ASFs that participate, will run an information campaign among their members (caregivers of students enrolled at each school) explaining them the study and providing a link to sign up for it via a designated Website. Tobacco Control Unit Research Team will then contact the potential participants and start their participation.

The intervention is an adapted intervention "Some things a better outside" developed by the Emory University. The intervention is based on 5 steps (Decide; Talk; Pick a date; Make it happen; and Keep it up) and is delivered during 6 weeks in 2-week intervals (first mailing, counselling call, and two other mailings). The intervention will be delivered only to the IG participants in the CG will not receive the intervention but may optionally receive it following the 6 months follow-up.

Data collection: 1) baseline; 2) at month 3 postbaseline; 3) at month 6 postbaseline. Primary outcome: prevalence of households with complete smoking ban in the homes at follow-ups (self-reported). Secondary outcomes: SHS exposure level at follow-ups (self-reported).

Second-hand tobacco smoke (SHS) is a mixture of smoke exhaled by a smoker and smoke from the burning end of a cigarette. There are more than 4,000 components in SHS, including toxic substances, irritants and, approximately 70 carcinogens. Since 2004, SHS is defined as carcinogenic to humans (Group 1) by the International Agency for Research on Cancer. Exposure to SHS is an important public health problem as it causes a number of life-threatening diseases, among others lung cancer, stroke, chronic obstructive pulmonary disease, and ischemic heart disease in adults. Moreover, children exposed to SHS are at an increased risk for sudden infant death syndrome, acute respiratory infections, otitis media, and more severe asthma. Globally, SHS exposure was the 13th-leading risk factor for deaths in 2019, accounting for 1.30 million deaths. It contributed to 37.0 million disability adjusted life years worldwide, with 11.2% of the burden seen among children under the age of 5 years. While exposure to SHS in most public places is addressed by smokefree regulations, smoking and, consequently, the exposure to SHS at private places, such as homes, is still prevalent and represents a significant public health challenge.

It is evaluated that globally approximately 40% of youth is exposed to SHS at home. In a survey conducted among schoolchildren in Terrassa (Barcelona) in 2006 we found similar results, 41% of children aged 12-13 years reported exposure to SHS at home. For younger ages, another survey we conducted in Barcelona in 2016 showed that 71% of children younger than 12 years were exposed to SHS and 26% of them were exposed to SHS at home. Previous research in Spain have shown that SHS exposure at home is strongly correlated with family structure, smoking rules in household, number of smokers and non-smokers at home and number of cigarettes smoked; moreover, social disparities exist in SHS exposure among children and therefore, the inequalities in SHS burden persist in the local population.

In Spain, a few initiatives have been undertaken to reduce SHS exposure in children. In 2006, the RESPIR·NET multi-level (individual, family, and school) school-based intervention to prevent the exposure to SHS among schoolchildren (12-14 years old) was developed and tested in the city of Terrassa (Barcelona). While crude data indicated that in the intervention group SHS exposure significantly decreased at home (-16.9%); after adjustment for potential confounders the changes showed to be non-significant. In 2008-2009, the BIBE study aimed to evaluate a brief intervention within the context of primary health care, directed to parents who smoke, in order to reduce SHS exposure of babies. A multicentre, open, cluster-randomised clinical trial showed that parents who received the intervention to avoid SHS better adopted the recommended strategies at home with reduced nicotine concentrations in babies' hair samples.

While these interventions did not target promotion of smoke-free homes specifically, a recent study, part of a larger TackSHS Project (www.tackshs.eu), aimed to design, implement and evaluate a "Measuring for change" intervention to create smoke-free homes among families with children from disadvantaged areas. The intervention, developed by the team of the University of Stirling, is based on providing remote air quality feedback to the participants via short messages and emails. While the intervention resulted in small but significant reduction of SHS exposure, it was not effective in creating smoke-free homes; in addition, the design requiring two home visits and installation of air quality monitors challenged the participants' recruitment.

In summary, currently in Spain a high proportion of households allow smoking resulting in unneglectable prevalence and burden of exposure to SHS at home among adults and children. No comprehensive and systematic support is offered at national or local levels for those who want to create smoke-free homes resulting in a significant gap in health prevention services. Therefore, there is an important need to offer such services to Spanish population.

The solution: adopting an evidence-based smoke-free intervention. In response to this need, we will test the effectiveness of an adapted brief evidence-based intervention to promote smoke-free homes initially developed by the University of Emory (PI: Prof. Michelle Kegler). This intervention was adopted, piloted and tested in a number of the US States and cities with excellent results, that given its minimal intervention nature, enables reaching a greater number of people. Additionally, the proposed intervention will target families with children to increase the potential impact on health burden from a reduced SHS exposure at homes. We aim to test the intervention in Catalonia with a view to its future scalability at the national level, ensuring comprehensive support for creating smoke-free homes as part of a service package available to schools and associations of students' families. Therefore, the main aim of this study is to evaluate the effectiveness of an evidence-based intervention to create smoke-free homes in households with children.

Inclusion Criteria:

• Adults (18 years or older)
• Live in a household with at least one minor (younger than 18 years old)
• Live in a household with at least one person who smokes
• Smoking is allowed at home (always or sometimes; everywhere or in some specific places, including balconies or terraces).
• Speak and understand Catalan or Spanish.

Exclusion Criteria:

• N/A