## 4 Discussion
Therefore, the integration of VR applications into traditional intervention protocols could increase their effectiveness and enhance participants' adherence to them by creating stimulating experiences. The present review underlines that VR systems can evoke a general positive change on the subjective and objective measurements in healthy adults and, consequently, could help them enhance their responses to stress. From a psychological point of view, at the basis of these applications is the user's sensation of leaving the current physical environment and being transported to the VR location [98]. The sense of presence can be influenced by several factors including technical-related aspects [99], intrapersonal factors [100], such as personality traits and social factors [98], and interaction with VR environments. Furthermore, another essential component of VR is immersion, which enables users to engage in digitally-recreated real-world environments and activities [101], simultaneously allowing them to experience if what they do there is similar to the real experience [102; 103]. The ability of VR technology to recreate complex elements of real life makes presence and immersion salient factors for the relevant interventions [43]. In this way, VR-supported interventions can reconstruct personal experiences by motivating individuals to employ new techniques in a protected environment and to modify habitual reactions to stressful situations. In this sense, users can be exposed to a wide range of stress management techniques, practice them in different VR environments, and transfer them to real-life scenarios. Although VR characteristics can potentially define the quality of users' experiences and VR's effectiveness to evoke positive changes, only three studies of the sample (18.75%) used questionnaires to capture the feeling of presence after VR exposure [46; 51; 52], and two other studies (12.5%) explored the level of immersion [54; 55]. One would say that this was one of the strongest commonalities within the investigated articles, which, however, should stimulate more research in the field, striving for well-designed interventions to facilitate a user's presence and immersion into VR activities. While the methodological assessment of the studies is of primary importance for systematic reviews, it would be an omission not to emphasize the similar nature of the selected study designs. The study designs employed were mainly between-subjects experiments that were conducted in laboratories. This implies that the guidelines for randomized controlled trials were not followed. An exception to this was the study of [PERSON] et al. [47] in which the authors conducted a double-blind, randomized, controlled, between-subjects experiment. This is perhaps an indication that strict study regimes for stress management among healthy populations in VR should be determined in the near future. The common nature of study designs may also explain why statistical assessment and comparisons of the main outcomes were difficult. In addition, the vast majority of the examined studies (93.75%) were conducted only in one session, expect for the study of [PERSON] and [PERSON] [35]. Despite several studies providing evidence for the positive effects of VR on mental health, individuals might have returned later to stressed levels or might have failed to integrate the relaxation techniques into their daily routine, especially without continued support. One could mention that the lack of longer intervention periods and follow-ups could lead to questions about the quality of studies and their findings. However, the careful investigation of non-randomized evidence can provide estimates of the direction and size of the produced effects [104]. This is particularly important for recently developed research fields such as VR, which demand evidence to move toward full-scale, repeatable, robust interventions [81].