This study examined self-rated general health (SRH) among exclusive e-cigarette users and exclusive cigarette smokers using a nationally representative sample of Scottish adults. Our findings indicate that exclusive e-cigarette users consistently reported better SRH than cigarette smokers. This association remained significant after adjusting for demographic, socioeconomic, and health-related factors, such as age, sex, Scottish Index of Multiple Deprivation, marital status, ethnicity, alcohol consumption, physical activity, longstanding health conditions and age of smoking initiation.

Specifically, exclusive e-cigarette users reported better SRH compared to heavy smokers (≥ 20 cigarettes/day), who had significantly lower odds of reporting better SRH. This suggests that exclusive e-cigarette users perceive better health than heavy smokers, which may reflect potential harm reduction benefits, aligning with previous research from England that found similar associations after adjusting for comparable covariates [15]. Similarly, the majority of e-cigarette users perceived better health, according to a cross-sectional survey of nine vape shops across Louisville, Kentucky, designed to capture a diverse customer demographic [14]. A study from Hungary further supports these findings, showing that e-cigarette-only users reported fewer adverse health events and greater perceived health improvements compared to dual users [26]. When compared to exclusive e-cigarette users, moderate smokers (10 to fewer than 20 cigarettes per day) also had lower odds of reporting better self-rated health. However, no significant differences in self-rated health were observed between exclusive e-cigarette users and light smokers (fewer than 10 cigarettes per day). This implies light smokers might consider themselves healthier due to consuming fewer cigarettes [2]. However, it is important to note that even light smoking carries substantial health risks, and complete cessation of all nicotine products remains the most effective strategy for achieving long-term health benefits.

Sensitivity analyses confirmed that exclusive e‑cigarette users consistently reported better self‑rated health than exclusive cigarette smokers. Additional analyses showed that among exclusive e‑cigarette users, self‑rated health remained stable regardless of prior smoking history. This suggests that once individuals switch entirely to e‑cigarettes, their perceived health status is unaffected by whether they were former smokers or had never smoked. These findings underline e-cigarettes’ potential for harm reduction as switching may offer similar perceived health benefits to both former cigarette smokers and exclusive e-cigarette users without prior smoking history. Further analyses revealed no significant differences in self‑rated health between exclusive cigarette users who had previously vaped and those who had never vaped. Nearly half of exclusive cigarette smokers in this study had used e‑cigarettes at some point, indicating possible challenges, such as misinformation, insufficient support, limited access to appropriate products, inadequate harm reduction education, difficulty adjusting to new devices, social influences favoring smoking, and personal preferences for cigarettes. These results highlight the need for supportive interventions that encourage switching or complete cessation by providing counseling, community support, and clear guidance on e‑cigarette use.

While SRH is a valuable holistic measure of health, it is inherently subjective and influenced by individual perceptions, cultural norms, and psychological factors [2, 27]. People’s assessments of their own health can vary based on expectations, awareness of health information, and psychological state [28]. Therefore, caution is advised when interpreting these findings, as SRH may not always align perfectly with objective health indicators or clinical evaluations [7]. For instance, individuals who switch to e-cigarettes might perceive them as less harmful due to public health messaging or personal beliefs, positively influencing their self-assessment of health regardless of actual physiological changes. This potential bias underlines the importance of combining SRH with objective health data to comprehensively assess health outcomes related to e-cigarette use.

Evidence suggests that SRH is meaningfully associated with objective health outcomes. Studies have demonstrated strong correlations between SRH and specific health conditions, including diseases like epilepsy, cancer, and diabetes, across various age groups [29]. Poorer SRH is consistently linked to a higher prevalence of diseases and abnormalities in laboratory parameters, such as cardio-cerebral vascular diseases and hemoglobin levels [30]. These findings emphasize the value of integrating subjective perceptions with objective measures to gain a comprehensive understanding of health outcomes. By doing so, researchers and policymakers can better assess the potential impacts of e-cigarette use on population health.

Several studies have reported potential cardiovascular and respiratory benefits for smokers who switch to e-cigarettes. Individuals transitioning to e-cigarettes have experienced improvements in cardiovascular parameters, such as reductions in systolic blood pressure, enhanced endothelial function, and decreased arterial stiffness [31,32,33,34,35]. Improvements in lung function and decreases in airway resistance have also been observed [36, 37]. A recent systematic review and meta-analysis found that exposure to tobacco-specific nitrosamines—potent carcinogens in tobacco smoke—was significantly lower among exclusive e-cigarette users compared to exclusive cigarette smokers [38]. A study assessing biomarkers of exposure (BoE) and biomarkers of potential harm (BoPH) among exclusive e-cigarette users, current smokers, former smokers, and never-smokers revealed that exclusive e-cigarette users had significantly lower levels of BoE to specific tobacco smoke toxicants compared to current smokers [39]. Their BoPH levels, associated with biological processes linked to smoking-related diseases and oxidative stress, were more favorable than those of current smokers [39]. Another study corroborated these findings, showing that exclusive e-cigarette users had lower concentrations of harmful constituents than cigarette smokers, suggesting reduced exposure to toxicants [40]. These objective findings support the notion that e-cigarettes may reduce harm compared to traditional cigarettes, at least in the short term, aligning with the better SRH reported by exclusive e-cigarette users in our study.

However, not all studies have found positive health outcomes associated with switching to e-cigarettes. Some research indicates no significant improvements in cardiovascular or respiratory health markers for individuals who transition from traditional cigarettes to e-cigarettes. In some instances, e-cigarette use has been linked to adverse effects on these objective health parameters [41,42,43,44]. For example, one study found that e-cigarette use is associated with increased heart rate and blood pressure, similar to the effects of traditional cigarettes, raising concerns about the potential lack of cardiovascular benefits [45]. Another study reported that e-cigarette use could lead to increased airway resistance and inflammation, suggesting respiratory risks [46]. Additionally, a review highlighted that although exclusive e-cigarette users may have lower levels of certain harmful biomarkers compared to smokers, they still exhibit elevated levels relative to non-smokers, implying that e-cigarettes may reduce but not eliminate exposure to harmful substances [47]. These mixed results suggest that while e-cigarettes may reduce exposure to certain toxic substances present in tobacco smoke, the extent of health benefits may vary among users. Factors, such as individual health conditions, duration and intensity of e-cigarette use, and differences in device types and e-liquids could influence these outcomes [15].

Beyond objective data, SRH plays a key role in harm reduction discussions. While objective measures like biomarkers and clinical parameters provide critical evidence of biological impacts, SRH offers valuable insights into individuals’ perceptions of their health and well-being [48]. These subjective evaluations are integral to understanding how people feel about their health, which can influence behavior change and adherence to harm reduction strategies. For instance, a smoker who switches to e-cigarettes may report improved SRH even before measurable changes in biomarkers are evident, reflecting perceived benefits, such as reduced breathlessness, improved energy levels, or less stigma associated with smoking. SRH also captures the broader real-world impact of harm reduction tools like e-cigarettes, encompassing dimensions of physical, mental, and social health. Moreover, SRH is a strong predictor of long-term health outcomes and mortality [49], making it an important metric alongside objective data. Including SRH in harm reduction research provides a more comprehensive understanding of the potential benefits and challenges associated with switching to e-cigarettes, aligning public health interventions with individuals’ lived experiences and perceptions.

A strength of this study is the large sample size and inclusion of diverse demographic, socioeconomic, and health-related covariates, allowing for robust adjustments and minimizing potential confounding. The use of generalized ordinal logistic regression accommodated the proportional odds assumption where necessary, providing insights into the association between nicotine product use and SRH. Sensitivity analyses, including alternative SRH categorizations and adjustment for temporal effects, confirmed the consistency of the findings.

However, this study has several limitations. First, the cross-sectional design prevents us from inferring causality [50, 51] or determining the directionality of the association between nicotine product use and SRH. While the association persisted after adjusting for healthy behaviors, suggesting these factors do not fully explain the relationship, longitudinal studies are needed to clarify the causal pathways. Second, SRH is subjective and may be influenced by individual perceptions, cultural norms, and psychological biases. E-cigarette users may rate their health more favorably due to perceived reductions in harm from public health messaging or personal beliefs, regardless of actual physiological changes. This could lead to an overestimation of health benefits. While the consistency of results across multiple models adjusted for various factors reduces the likelihood that subjective bias fully explains the findings, the potential for bias remains.

Third, residual confounding from unmeasured factors—such as diet, stress levels, or detailed patterns of e-cigarette use (e.g., device types, nicotine concentration, duration, usage frequency)—could influence the results. Furthermore, while cigarette smoking was stratified by intensity (light, moderate, heavy), e-cigarette use was analyzed as a single category. This approach assumes homogeneity among e-cigarette users and could dilute the potential impact of very frequent e-cigarette use on SRH. Stratifying e-cigarette users by use frequency may provide additional insights as frequent users might perceive their health differently than occasional users. However, the lack of detailed information on e-cigarette use patterns limits our ability to conduct such analyses. Given that SRH is subjective and influenced by present health perceptions, we believe our findings remain robust as they capture general differences in perceived health between exclusive e-cigarette users and cigarette smokers rather than focusing on within-group variability among e-cigarette users.

Although we accounted for a broad range of covariates, the possibility of residual confounding cannot be entirely ruled out. Additionally, the study excluded certain groups, such as dual users and individuals using other nicotine products (e.g., cigars or pipes), which may limit the generalizability of the findings to the broader population of nicotine users. Focusing on exclusive users allowed for a more precise examination of the independent association between product type and SRH but may not reflect the experiences of all nicotine users. Finally, reliance on self-reported data, including SRH and nicotine use, introduces the potential for reporting bias. Participants may underreport or misreport their smoking or vaping habits due to social desirability or recall errors. However, the use of validated survey instruments and standardized questions minimizes this risk.

Despite these limitations, the study’s strengths—including robust sensitivity analyses, a focus on exclusive users, and adjustments for a wide range of confounders—enhance the validity of the results. Future research employing longitudinal designs and incorporating objective biomarkers alongside SRH will provide a more comprehensive understanding of the health impacts of e-cigarette use. Additionally, studies exploring diverse populations beyond Scottish adults would help determine the generalizability of these findings to other settings.