**1. Introduction**

According to the estimates of the World Health Organization (WHO), each year 150,000 children and adolescents die as a consequence of exposure to second hand smoke (SHS) [1]. Scientifically proven is the relationship between SHS exposure and premature births, lower birth weight and irreversible

organ damage. The latter include respiratory diseases such as asthma, sudden infant death syndrome and otitis media [2].

In Germany, about 20% of children are exposed to SHS inside the home environment [3] compared to 11% in the US [4] and 79% in Indonesia as examples for countries with relatively small/high exposure levels [5]. While the introduction of smoke-free laws in Germany between 2007 and 2008 led to a considerable reduction of SHS exposure in public places [6], there is no legislation with respect to smoking at home or in cars [7]. The highest levels of SHS exposure are generally found among children of disadvantaged and migrant families [3,8–12]. One explanation for this could be that individuals with lower socio-economic status (SES) are less aware of the detrimental health effects of SHS and have less knowledge regarding strategies to reduce SHS exposure [2,3,13]. Therefore, it has been recommended that interventions should be tailored to the needs of families in difficult social or economic situations and should take into account cultural barriers [3,9,14–17].

The optimal intervention would be to convince parents to stop smoking. However, this approach is frequently not successful [18,19]. Unfortunately, the second best approach—promoting a reduction of SHS exposure in the home environment—has also resulted in only small effects in most studies [19,20]. Practical, social, financial, cultural, and personal issues make it difficult for disadvantaged parents to protect their children from SHS [15,16,21]. To our knowledge, the intervention studies carried out so far followed a top-down rather than a participatory approach [18,19]. However, the latter approach is recommended in order to reach disadvantaged parts of the population [22,23]. For this, a mixed methods iterative design assessing the target populations' perspectives via qualitative studies followed by the development of intervention strategies, which are then evaluated using quantitative methods, is desirable [24].

Furthermore, most of the intervention studies targeted at the reduction of SHS exposure in children were carried out in health settings, while the use of media as an access path was rarely considered [11]. A relatively new option of employing media for interventions is the distribution of health-related information via electronic media (so called "e-health"), especially mobile communication devices and social online networks ("m-health"). One of their main advantages is that they potentially reach a large number of users at low costs as compared to interpersonal counselling. More importantly, they have the potential to reach disadvantaged groups which are hard to approach with conventional methods [25]. A Canadian study, for example, successfully employed a smartphone application for coaching diabetes patients with a rather low socio-economic status [26]. For the effective planning of such m-health interventions, the involvement of the target group from the first development step is crucial [27].

Using a largely participatory approach, we therefore aimed at identifying media channels and appropriate content for an m-health campaign increasing knowledge about the risks of second hand smoke exposure and appropriate measures for exposure reduction among disadvantaged caregivers in Germany.
