Background:
E-cigarettes have become increasingly popular. We examined perceptions of e-cigarettes, and their associations with e-cigarette use, frequency of use, and use susceptibility among young adults in Hong Kong.

Methods:
An online survey was administered to 1,186 Hong Kong residents aged 18-35 in 2016-17. On a 0-10 visual scale, participants rated the perceived harm of e-cigarettes, perceived harm of secondhand exposure to e-cigarette aerosols, and perceived addictiveness. An overall perception score was calculated by averaging the values of non-missing perception items. Multinomial logistic regression examined the relationship of the overall perception score with former and current e-cigarette use relative to never use, controlling for age, gender, education, place of birth, current cigarette smoking, and perceived popularity of e-cigarettes among peers. Bivariate exact logistic regression assessed the association between perceptions and frequency of e-cigarette use (“≥3 days” vs. “1-2 days” in past 30-day) among current users. Multivariate logistic regression assessed the relationship between perceptions and e-cigarette susceptibility among never users.

Results:
97.2% of participants were aware of e-cigarettes, and 16.1% had ever used e-cigarettes (11.3% former users; 4.8% current users). Of current e-cigarette users, 63.2% reported infrequent use. Among never users, 34.0% were susceptible to e-cigarette use. E-cigarettes were perceived as less harmful and less addictive than cigarettes, particularly among current cigarette smokers. Low overall perception score was associated with former and current e-cigarette use, frequent use, and use susceptibility. Current cigarette smoking and perceived higher popularity of e-cigarettes were also related to e-cigarette use. Current cigarette smoking was associated with e-cigarette susceptibility.

Conclusions:
Continued surveillance on e-cigarette use is needed. Interventions must address the conceptions about e-cigarettes. Health communication messages emphasizing the harmful and addictive nature of e-cigarette use and secondhand exposure to e-cigarette aerosols, and health warning labels on e-cigarette packages may help reduce e-cigarette use in young people.