BACKGROUND-AIM:
Secondhand smoke exposure remains a major public health concern. In Spain, although smoking is banned in indoor public spaces, private environments such as homes can not be regulated, posing a risk of exposure—particularly for children. The aim was to assess whether the presence of children influenced indoor smoking practices.

METHODS:
In May 2025, two opportunistic surveys were conducted in Cantabria to explore smoking behaviours in domestic settings, considering the presence of children in the household, carried out by primary care nurses, one at information stands in healthcare centers, and another among minors from educational institutions. Smoking inside the home was defined as smoking in any domestic area, including balconies/terraces, windows, or indoor rooms. Data were analyzed using SPSS v20.

RESULTS:
A total of 5565 questionnaires were collected: 1966 from participants ?18 11 to 18 years old (49.5% girls) and 3599 from adults >18 years (61.7% women). Among adolescents, 3.9% were smokers and 3.9% regular e-cigarette users. Among adults, 20.8% were current smokers, 31.7% former smokers, and 45.2% never smokers; 1.7% were e-cigarette users. Among minors, 36.7% lived with at least one smoker and 5.7% with an e-cigarette user. A complete home smoking ban was reported by only 9.1% of respondents. Smoking most commonly occurred on terraces (53%), at windows (37.7%), or in indoors rooms (26.2%). Among adults, the prevalence of complete home smoking bans did not differ by the presence of children (90.5% vs. 91.8%; p = 0.62). However, partial restrictions differed in homes with children: smoking occurred more frequently on terraces (54.0% vs. 43.4%; p = 0.008) and less often indoors (24.6% vs. 40.4%; p < 0.001). In 97.6% of households, no one used electronic cigarettes.

CONCLUSIONS:
Complete smoking restrictions are not influenced by the presence of minors in the household. In homes with minors, however, behavioral patterns change under partial indoor smoking restrictions, with a significant increase in smoking on terraces. Even so, one in three minors is still exposed to tobacco smoke. Reports from minors and adults are consistent regarding smoking restrictions, enhancing the reliability of the results. Although the presence of minors reduces indoor smoking and shifts it to terraces, most homes remain far from completely smoke-free. This reflects a common misconception that smoking on terraces or near windows fully protects others from exposure. A key limitation of this study is that despite the high response rate, the small number of adults e-cigarette users limits the representativeness of the findings related to household vaping.