Introduction:
Potential effects of parental e-cigarette use on adolescent tobacco use are understudied but have implications for tobacco and e-cigarette control. We investigated the associations of parental cigarette and e-cigarette use with adolescent use of these products.

Methods:
A cross-sectional questionnaire survey was conducted in 26648 secondary school students (mean age 14.8 years, 54.7% boys) in Hong Kong in 2016/17. We examined the associations of paternal and maternal cigarette and e-cigarette use (study factors: abstinence [reference]/cigarette use only/dual use of cigarettes and e-cigarettes/e-cigarette use only) with cigarette and e-cigarette use stages (never, not susceptible [reference]/never, susceptible/ever, not current/current) in adolescents, with mutual adjustment of the study factors and adjustment of age, sex, and perceived family affluence.

Results:
In general, parental cigarette use only, dual use, and e-cigarette use only (vs abstinence) were all associated with adolescent cigarette and e-cigarette use. The associations were generally strongest for parental e-cigarette use only, followed by dual use and cigarette use only. For example, the adjusted odds ratios (AORs) of adolescent current cigarette use were 43.03 (95% CI 23.85-77.63) for maternal e-cigarette use only, 10.90 (6.25-19.01) for dual use, and 3.13 (2.65-3.71) for cigarette use only; the corresponding AORs of adolescent current e-cigarette use were 71.37 (37.83-134.64), 17.29 (10.95-27.30), and 2.98 (2.44-3.64).

Conclusions:
In Hong Kong adolescents, cigarette and e-cigarette use were generally more strongly associated with parental e-cigarette use than with parental cigarette use. These findings support the Government’s proposal to ban e-cigarettes to protect the health of young people.