The health effects of combustible tobacco product use and secondhand smoke (SHS) exposure are well established.¹ Over the past several decades, significant progress has occurred in the adoption of comprehensive smoke-free policies in indoor public places, including worksites, restaurants, and bars.² Public indoor smoke-free policies are strongly associated with the adoption of voluntary smoke-free rules in private settings such as homes and vehicles.³ Accordingly, the prevalence of voluntary smoke-free home (83.7%) and vehicle (78.1%) rules has also increased among U.S. adults over time.⁴

In recent years, the tobacco product landscape has evolved to include a variety of newer products, including e-cigarettes and other electronic vapor products (EVPs).⁵ In contrast to combustible tobacco products, EVPs do not produce sidestream emissions. Aerosol is only produced during activation of the device, some of which is exhaled into the environment as secondhand aerosol (SHA) where nonusers can be exposed.⁵ Although these products generally emit fewer toxicants than combustible tobacco products,⁵ SHA exposure can involuntarily expose nonusers, including children, to harmful and potentially harmful constituents such as nicotine, ultrafine particulates and volatile organic compounds, among others.⁵

Few studies have assessed voluntary rules prohibiting EVP use in homes and vehicles.^6–8 In the U.S., two small, non-nationally representative studies reported that 6% of current cigarette smokers,⁶ and 32% of current and former smokers,⁷ had rules prohibiting EVP use in their home; no current smokers reported having rules against EVP use in their vehicles.⁶ To date, only one study has assessed EVP rules in homes among tobacco product users and non-users.⁸ This nationally-representative study, conducted in Great Britain, reported that 57.5% of adults did not allow EVP use inside their homes, but did not report on rules inside vehicles.⁸

To date, no nationally-representative study has assessed the prevalence of voluntary rules regarding EVP use inside U.S. homes, and no national or international study has assessed the prevalence of voluntary rules for EVP use in vehicles. To address this knowledge gap, this study assessed the current prevalence and socio-demographic correlates of self-reported rules prohibiting EVP use inside homes and personal vehicles among U.S. adults.

Inside homes, 58.6% of adults did not allow EVP use; 7.7% partially allowed, 10.1% fully allowed, and 23.6% were unsure of the EVP rules. Never EVP users (63.0%) had a higher prevalence of not allowing EVP use at home compared to those who had ever tried EVPs but were not current users (38.5%) or current (21.6%) EVP users (p<0.05). The prevalence of not allowing EVP use in homes was higher for never cigarette smokers (67.5%) than former (57.4%) or current smokers (30.1%; p<0.05) and non-users of other tobacco products (59.7%) than current users (43.0%; p<0.05) (Table 1).

Inside vehicles, 63.8% did not allow, 6.0% partially allowed, 8.9% fully allowed, and 21.4% did not know or were unsure of the EVP rules. By EVP use status, 68.7% of never users, 41.3% of those who had ever tried EVPs but were not current users, and 20.6% of current EVP users reported not allowing EVP use inside vehicles. The prevalence of not allowing EVP use in vehicles was higher for never cigarette smokers (72.8%) than former (64.4%) or current smokers (30.7%; p<0.05) and among non-users of other tobacco products (64.9%) than current users (45.8%; p<0.05) (Table 1).

The adjusted likelihood of not allowing EVP use inside homes and vehicles was greater among adults with a college degree (home: aPR=1.27, CI=1.11–1.45; vehicle: aPR=1.16, CI=1.03–1.31) compared to less than high school; those with a child aged <18 years (home: aPR=1.15, CI=1.09–1.22; vehicle: aPR=1.12, CI=1.07–1.18) compared to no child; and higher annual household income categories compared to less than $15,000 (Table 2). The likelihood of not allowing EVP use was lower among non-Hispanic black respondents (home: aPR=0.85, CI=0.76–0.95; vehicle: aPR=0.89, CI=0.82–0.98) than non-Hispanic white; and those living with an EVP user (home: aPR=0.68, CI=0.55–0.84; vehicle: aPR=0.71, CI=0.59–0.86) or other tobacco product user (home: aPR=0.87, CI=0.80–0.95; vehicle: aPR=0.84, CI=0.77–0.91) than not living with respective tobacco product users.

Compared to respective non-users, the adjusted likelihood of not allowing EVP use inside homes was lower among current EVP users (aPR=0.66, CI=0.48–0.90), those who had tried but were not current EVP users (aPR=0.77, CI=0.68–0.86), and current (aPR=0.73, CI=0.64–0.83) and former (aPR=0.92, CI=0.86–0.98) cigarette smokers. Not allowing EVP use inside vehicles was less likely among current EVP users (aPR=0.59, CI=0.43–0.81), those who had tried but were not current EVP users (aPR=0.78, CI=0.70–0.86), current (aPR=0.68, CI=0.60–0.77) and former (aPR=0.92, CI=0.86–0.97) cigarette smokers, and current users of other tobacco products (aPR=0.85, CI=0.74–0.97) than respective non-users.

In 2017, approximately 6 in 10 adults in the U.S. reported having rules that prohibited EVP use inside their homes (58.6%) and vehicles (63.8%). This is lower than previously reported estimates of smoke-free rules in homes (83.7%) and vehicles (78.1%) for combustible tobacco products.⁴ These findings may reflect limited knowledge of the harmful and potentially harmful constituents documented in SHA or common EVP marketing strategies, some of which have promoted their use in locations where combustible tobacco product smoking is prohibited.⁵

Over 20% of adults reported being unsure of the rules for EVP use inside homes and vehicles. Limited knowledge or awareness of EVPs,^9,10 varied harm perceptions toward SHA exposure,¹¹ limited experience with SHA exposures,^8,12 or other factors may have contributed to a lack of definitive rules related to EVP use in these environments. Thus, these individuals may represent an important segment of the population for targeted educational interventions to promote EVP rules in these locations.

Variations in prohibiting EVP use inside homes and vehicles were observed by tobacco product use status. Only about 20% of current EVP users, 30% of current cigarette smokers, and 40% of other tobacco product users reported not allowing EVP use inside these locations. Thus, opportunities exist to educate all tobacco product users about the harms of SHA exposure and the importance of including EVPs in voluntary smoke-free rules in private settings.

Approximately one-third of respondents with children either did not prohibit EVP use or were unsure of the rules toward EVP use inside their home or vehicle. Secondhand exposure to emissions from EVPs and conventional cigarettes can result in similar increases in serum cotinine levels among never tobacco users,¹³ suggesting comparable nicotine exposures from SHS and SHA. The U.S. Surgeon General has concluded that nicotine exposure during adolescence can harm the developing adolescent brain.⁵ SHA also can contain other harmful constituents that can be particularly problematic for children, including ultrafine particulates, which can be inhaled deeply into the lungs. Opportunities exist to educate parents about the importance of protecting children from SHA exposure inside homes and vehicles.

Non-Hispanic black respondents and those with lower income and education were less likely to report not allowing EVP use inside homes and vehicles, similar to previous findings for rules toward combustible tobacco products.⁴ Furthermore, prohibiting EVP use in these locations was less likely among respondents who lived with EVP and other tobacco product users. These variations underscore the importance of targeted efforts to educate these populations about the harms of SHA exposure, particularly those with the greatest burden of exposure.

In recent decades, there has been significant progress in the adoption of smoke-free policies in public places.² However, policies that explicitly address EVP emissions in public places are limited. As of December 2017, 9 U.S. states, Washington D.C., Puerto Rico, and about 500 municipalities have included EVPs in comprehensive smoke-free legislation,^14,15 while five states prohibit EVP use inside personal vehicles when children are present.¹⁶ Although the inclusion of EVPs in smoke-free policies is increasing,¹⁷ most of the U.S. population currently lives in a state where bystanders may be exposed to SHA in public places.¹⁵ Thus, voluntary smoke-free rules that include EVPs inside homes and vehicles may further protect non-users from secondhand emissions to these products. Such rules are particularly important for children, who may spend a greater amount of time in these private spaces.¹⁸ Furthermore, voluntary smoke-free rules in these environments that include EVPs could help prevent the renormalization of tobacco product use, particularly among youth.⁵ EVPs and SHA can resemble combustible tobacco products and SHS, and youth are particularly vulnerable to visual cues and other social norms.^5,19

This paper is subject to at least three limitations. First, participants were drawn from an Internet-based panel, which may limit generalizability compared to traditional population-based surveys. Second, the limited sample size prevented the ability to report results separately for never and ever EVP users. Finally, a large percentage of respondents reported they did not know, or were unsure of, the rules toward EVP use inside their home or vehicle. Although respondents who selected this response were maintained for multivariable-adjusted analyses, they were considered to have no definitive rule to prohibit the use of EVPs in these locations.

In 2017, a majority of adults in the U.S. had voluntary rules prohibiting the use of EVPs inside their homes and vehicles. However, variations existed by EVP and other tobacco product use. Further, many adults reported being unsure of the rules regarding EVP use in these locations. Opportunities exist to educate all adults on the importance of voluntary rules that protect non-users from secondhand emissions to all tobacco products, including e-cigarettes and other electronic vapor products.