As a common mental disorder, depression does not refer to short-term mood fluctuations but a persistent state of negative mood, such as sadness, emptiness, or irritability, which is usually accompanied by somatic and cognitive changes [35]. According to the WHO, the worldwide prevalence of depression is 3.8%, and about 280 million people globally have been affected by depression in recent years [23]. In China, a nationwide survey found the lifetime and 12-month prevalence of depression were 6.9% and 3.6%, respectively [36]. Moreover, studies have revealed that the incidence of depression tends to be young, with many young people in China experiencing an episode [37].

As depression can lead a person toward myriad means of harm, identifying contributing factors and underlying mechanisms has been the focus of considerable research. It is, to date, generally believed that depression is caused by a complicated interaction of biological, psychological and social variables [38]. Substantial research has revealed that depression is significantly correlated with both individuals’ personal characteristics (including demographic and psychological attributes) and external environmental variables (e.g., random events, social ties, and cultural influences) [39]. Social support, as a kind of important resource from others, is on the list of the protective factors of depression, i.e., support from social networks can play the role of buffer between adversities and individuals’ mental health and alleviate the likelihood of depression [40]. Social support refers to the material, emotional, and informational assistance obtained from one’s social networks, which usually reflects the closeness and quality of a person’s connectedness with others [41]. In some academic literature, social support is further classified as received social support and perceived social support [42]. The former emphasizes practical or visible assistance, while the latter highlights the perception of the available resources and subjective experience of being respected, understood, and supported in social relations [43]. Some studies point out that perceived social support as a type of psychological reality can exert more influence than received social support on individuals’ mental health [44]. Considerable research, including both cross-sectional and longitudinal studies, has found perceived social support to be significantly negatively related to depression [45,46,47]. Perceived social support is regarded as helpful for absorbing the impact of adversities and strengthening individuals’ courage and confidence to deal with life’s challenges, and hence, can reduce the risk of depression [48]. For example, one study based on the analysis of old people in Ireland found that perceived social support was a significant negative predictor of later-life depressive symptoms among those once exposed to childhood adversity [49]. On the contrary, lack of perceived social support was found to predict depression [50,51,52]. For instance, two researchers in a study on female twins found the risk of depression was positively associated with tension, disagreements, and criticism in interpersonal relationships [53]. Although a large number of studies conducted in various social groups have tested the link between perceived social support and depression, few studies have examined this relationship among China’s unemployed youths. In addition, the potential mechanisms accounting for the correlation between perceived social support and depression have not been fully explored [54]. Hence, the present study attempted to further examine the underlying process linking perceived social support and depression through a survey of unemployed Chinese youths.

In the process of exploring the risk factors of depression, increasing attention has been paid to difficulties with emotion regulation in recent years. Emotion-regulation difficulties were defined as deficits in modulating emotions, especially those for managing negative emotional experiences and expression, thus hindering the formation of adaptative emotions and hence affecting individuals’ mental health [55,56,57]. According to John and Gross, difficulties in emotion regulation are usually embodied in two key interactive processes: emotional insight and behaviors triggered by an emotional response [58]. Specifically, emotion-regulation difficulties include denial of emotion, emotional consciousness defects, and lack of clarity regarding emotion in the first process and impairments associated with the second process, such as a lack of effective emotion-management strategies or ability to control impulses or engage in goal-directed activities when distressed [59,60]. Previous studies have examined the association between emotion-regulation difficulties and some maladaptive behavioral issues (e.g., anxiety, post-traumatic stress disorder, and sleep disturbance) [61,62], and recent research revealed that emotion dysregulation caused by emotion-regulation difficulties, was also significantly positively related to depression [57,63,64,65]. For example, through a survey of a sample of 64 Norwegian adolescents, Visted and colleagues found a lack of positive emotion-regulating strategies and that adopting maladaptive methods, such as rumination and suppression may result in the persistence of a depressive mood and increase the risk of onset or relapse of depression [66]. In comparison, fewer emotion-regulation difficulties were found to be associated with reduced depressive symptoms. For example, an internet-based longitudinal study conducted during the COVID-19 pandemic reported that a decrease in emotion-regulation difficulties can significantly predict a reduction in anxiety and depression [67]. Emotion regulation was proposed to be a context-dependent process that can be affected by environmental variables [68]. Some research found that perceived social support could enhance people’s emotion-modulating abilities and reduce emotion-regulation difficulties [69,70,71]. English and colleagues suggested that strong ties with and more support from others help the emotional adaptation process by encouraging the utilization of such positive emotion-regulation strategies as reappraisal while decreasing the adoption of negative emotion-regulation strategies, such as expression suppression [69]. Moreover, a survey of Venezuelan migrants in Peru confirmed that the perception of support from family members can predict the utilization of reappraisal strategies and decrease emotion dysregulation [72]. Taken together, higher degrees of emotion-regulation difficulties are correlated with higher levels of risk of depressive symptoms but lower levels of perception of support from others. In addition, some studies proposed that emotion-regulation difficulties served as mediators between perceived social support and mental health [70,71]. Based on the above-mentioned correlations, we infer that difficulties in emotion regulation mediate the relationship between perceived social support and depression. However, this mediating model has not been tested by empirical research.

Besides risk factors, protective factors of depression are also a focus of scholars’ attention. A large number of studies have emphasized the protective effect of self-efficacy on depression [73,74]. Self-efficacy refers to one’s belief and confidence in his or her abilities to plan and perform certain actions to achieve desirable goals [75]. According to Bandura, self-efficacy helps individuals positively react to challenges and manage and control their life situations [76]; hence, people with more self-efficacy can cope with adversities calmly and avoid negative impacts on their mental health. This theoretical suggestion has been confirmed by recent research. Some studies have found self-efficacy to be negatively associated with depression [77,78,79,80]. For instance, an empirical study investigated a group of American cancer survivors and found that less self-efficacy was associated with more severe depressive symptoms [74], whereas another study reported that participation in training programs aimed at improving self-efficacy significantly decreased the depression scores of pregnant women in Iran [81]. In addition, some studies suggested that self-efficacy can also be affected by interpersonal processes, such as social interaction and social support [82,83,84,85]. For example, Siciliano argued that self-efficacy can be strengthened by relevant knowledge and beliefs accessed from the individual’s social network [86]. Indeed, there is evidence to support the positive correlation between social support and self-efficacy, i.e., people with a higher level of perceived social support often feel more confident in their abilities [87,88]. Hence, self-efficacy is positively associated with perceived social support while negatively related to depression. Moreover, some studies have empirically confirmed the mediating role of self-efficacy between some environmental variables (e.g., stressful life events, intimate partner violence) and depression [73,89]. Considering all these relationships, self-efficacy may be expected to mediate the link between perceived social support and depression, but few empirical studies have rigorously tested this mediating relationship.