Background: Thirdhand smoke (THS) contains toxic residues, including carcinogens, which persist on surfaces and clothes even after cigarette smoke dissipates. The public awareness of THS and its health effects remain low. Objective: This study examined beliefs about THS among Chinese-speaking former smokers and their non-smoking family members, before and after participating in a family-based THS education program. Methods: We implemented a 2-week THS education intervention delivered by lay health workers with 30 Chinese American dyads (N=60) residing in Northern California, consisting of former smokers who quit within the past 2 years and their family members. THS beliefs were assessed using the Beliefs About Thirdhand Smoke (BATHS) questionnaire administered at pre- and postintervention. Focus groups with 8 former smokers and 7 family participants were conducted. We used multivariable regression with Generalized Estimating Equations to account for time points and household correlations to assess changes in BATHS scores (Overall, Persistence and Health subscales). Focus group transcripts underwent independent coding by two researchers and thematic analysis. Results: The study sample included 30 male former smokers (37% with slight to mild craving for smoking), and 30 family members (97% female) who never smoked. A majority (82%) spoke English less than well, 83% were married, 58% lived with children and 27% with current smokers. All multivariable models showed a significant time x role (former smokers vs family) interaction (p < 0.05). Former smokers had lower BATHS scores than their family at preintervention (p < 0.01), but their scores became similar at post-intervention. Former smokers’ BATHS scores increased from pre- to post-intervention (Overall: p=0.02; Persistence: p=0.03; Health: p=0.04) while family had no significant change. Prominent themes from focus groups supported gaining new knowledge for both persistence and health effects of THS. Both former smokers and family members appreciated learning about cleaning methods and both shared increased family discussions and collaboration in household cleaning post intervention. Conclusion: THS education impacts former smokers and their non-smoking family members differently. Family-based interventions are promising to align beliefs and promote collaboration within households in addressing THS. Future randomized controlled trials should investigate broader impacts of the program on enhancing support for motivating quitting for current smokers, maintaining smoking abstinence, and in reducing THS exposure.

Significance: Thirdhand smoke (THS), which includes secondhand smoke contami- nants, can be re-emitted and re-suspended into the air and are embedded into carpets, floors, and clothing. The awareness of THS and the health impacts from exposure to its harmful residues is low in the general population of the United States, especially in immigrant communities where smoking remains prevalent. Our study implemented a THS family-based intervention to promote THS awareness among Chinese American immigrants. Methods: The THS intervention included an education and home cleaning component delivered by lay health workers to 30 Chinese American dyads (N=60). Dyads consisted of former smokers who quit within the last two years and their non-smoking family member living in the same household. Participants completed pre- and post-in- tervention survey interviews and a sub-sample (N=15; 8 former smokers and 7 family members) participated in a post-intervention focus group. Multivariable regression adjusted for dyadic data was conducted to compare pre- and post-intervention changes in the Beliefs About Thirdhand Smoke (BATHS) overall and subscale (Persistence and Health) scores. Transcriptions from focus group interviews, conducted in Cantonese, were transcribed and translated, coded by two independent researchers and themati- cally analyzed using Dedoose. Results: All participants were born outside the US and 59% immigrated at age 30 or older (range: 7 to 63 years old). A majority (82%) spoke English less than “well” and 87% were married. BATHS scores analyses suggested that former smokers increased their THS awareness from pre- to post-intervention: BATHS Overall (M=3.95 [SD=0.50], p=0.021); Persistence (M=3.95 [SD=0.48], p=0.031) and Health (M=3.94 [SD=0.58], p=0.038), and their post-intervention THS scores became similar to the BATH scores of non-smoking family members which did not change at post-intervention. Thematic analyses of focus group interviews revealed emerging themes highlighting impacts on former smokers in increasing THS knowledge and strengthening desires to create dialogue about tobacco use with friends; for example, a former smoker shared “I will share my [THS] knowledge with others. I think it will help [my friends] as well.” Conclusion: A family-based THS education intervention has promising impacts to advance tobacco control in Chinese American immigrant communities by providing new THS knowledge and encouraging former smokers to become agents of change. Future research on empowering former smokers to become effective agents of change to promote tobacco-free communities is warranted.