Introduction: The knowledge and beliefs about what is thirdhand smoke (THS) are limited. Our objective is to characterize the knowledge and beliefs about THS in parents of children under 3 years old in Spain.
Methods: A cross-sectional study (n = 1406 parents) was conducted online in 2017. We collected information about the knowledge of THS given later, written information with the definition of THS, and asking about beliefs of the effects of THS on children's health.
Results: A total of 27% of the respondents had heard about THS. We only found significant differences among smoking status, being the smokers who declare higher knowledge about THS. A total of 86% of the respondents believed that THS is harmful to their children with statistically significant differences according to educational level, higher among parents with a university degree (ORa = 2.6), and according to the previous knowledge on THS (ORa = 2.1).
Conclusions: This is the first study in Europe to describe the knowledge and belief of THS. Around 3 out of 10 parents have heard about THS and more than 8 out of 10 parents believed that THS is harmful to their children. Currently, they were not aware of THS but after providing brief information about it, most of them agreed that THS exposure is harmful to their children.