The novel coronavirus disease-2019 (COVID-19) was first detected in December 2019 and has since become a pandemic. Thereafter, on January 30, 2020, the World Health Organization (WHO) declared COVID-19 a public health emergency of international concern [1]. The virus has a short incubation period, rapid onset of symptoms, rapid change of symptoms, and is highly contagious. Consequently, COVID-19 poses a significant threat to patients as well as healthy individuals [2]. The COVID-19 pandemic is not limited to physical illness or death, but has brought about a period of change, ranging from sudden changes in the daily lives of individuals to global economic crises and socio-cultural changes [3].

Following the first confirmed case of COVID-19 reported in Korea on January 20, 2020, social distancing was introduced on February 29, 2020. On March 21, 2020, the government announced enhanced social distancing, which restricted the operation of multiuse facilities [4]. Subsequently, the distancing stage was adjusted according to the change in the number of confirmed patients, and all social distancing measures were lifted on April 18, 2022 [5]. Vaccinations in Korea started with medical personnel and those vulnerable to infection on February 26, 2021, and were subsequently administered to the whole country. According to the Korea Centers for Disease Control and Prevention (KCDC), 97.4% of adults were vaccinated up to the first shot, 96.6% were vaccinated up to the second shot, and 75.0% received a booster shot by midnight on August 19, 2022 [6].

The COVID-19 pandemic has affected the mental health of the general population. As per a survey conducted by the Korean Society for Traumatic Stress Studies and the Ministry of Health and Welfare in March, 2020, the risk groups for anxiety, depression, and suicidal ideation were 19.0%, 17.5%, and 9.7%, respectively. This is relatively high compared to the depression risk (3.79%) and the suicidal ideation rate (4.7%) identified in the 2018 Community Health Survey Report [7]. In a subsequent survey conducted in September 2020, anxiety risk had become 18.9%, which was at the same level as that in the March survey, while the risks for depression and suicidal ideation were 22.1% and 13.8%, respectively, both of which were relatively higher than those identified in the March survey [8]. According to a previous study in Korea, as the damage to society due to COVID-19 continues, accumulated stress on the general population has caused or exacerbated mental health problems [9]. The results of studies conducted in other countries on the mental health of the general population during the COVID-19 pandemic were similar. According to a systematic review, studies in various countries, such as China, Spain, Italy, Iran, the United States, Turkey, Nepal, and Denmark, also showed high anxiety, depression, post-traumatic stress disorder, and psychological stress in the population owing to the COVID-19 pandemic [10].

However, few studies have investigated how different characteristics of individuals affect their mental health during the pandemic. We attempted to identify the relationships between the stress caused by COVID-19 and various characteristics of individuals. Based on the statistical data and research results mentioned above, we hypothesized that individuals with psychiatric symptoms would be more vulnerable to stress than would individuals without such symptoms during the COVID-19 pandemic [7-10]. Since people suffered from economic problems during the pandemic, we hypothesized that the socioeconomic statuses of individuals would affect their stress [3]. Various experiences related to the COVID-19 pandemic were also expected to affect individuals’ stress. Therefore, we investigated demographic factors, psychosocial scales, and experiences related to COVID-19 to identify the factors affecting the stress and mental health of the participants during the pandemic.

This study attempted to identify the factors affecting the mental health and stress caused by COVID-19 among the public. According to the KCDC, 93.6% of adults were vaccinated up to the first shot, 91.6% were vaccinated up to the second shot, and 8.1% had received a booster shot by midnight on December 3, 2021, when this study was conducted [22]. Regarding the results of COVID-19-related experiences in the study, the vaccination rates of the participants in this study were similar to the total vaccination rate in Korea [22]. Further, 0.8% of the participants in this study responded that they had experienced COVID-19, and this figure is also similar considering the cumulative number of confirmed cases announced by the KCDC at the same time [22].

Insomnia severity exhibits a positive relationship with the degree of stress caused by COVID-19. These results are consistent with those of previous studies showing that elevated stress increases awareness of the surrounding environment and lowers the quality of sleep [23]. In terms of sleep physiology, the set point of the hypothalamic-pituitary-adrenal axis, which plays an important role in regulating the sleep-wake cycle, can be modulated and reset to other levels by stressful experiences, and this process may affect the quality of sleep [24]. Additionally, it can be assumed that sleep hygiene has become poorer as participants spend more time at home during the COVID-19 pandemic.

The study revealed that female sex had a positive relationship with the degree of stress caused by COVID-19, especially in terms of fear of infection and anger towards others. This is consistent with previous studies showing that women are more likely to experience psychological distress during the COVID-19 pandemic [25,26]. Best et al. [25] estimated that women are generally more likely to experience parenting stress and parenting responsibilities, and that their work responsibilities may worsen psychological distress during the pandemic [25,27]. Rodriguez-Besteiro et al. [26] reported that women presented relatively higher levels of perceived risk of COVID-19 than that presented by men owing to their emotional vulnerability. These interpretations may explain the results of women experiencing greater stress in this study.

The degree of income decline and the level of COVID-19 stress exhibited a positive relationship, especially in terms of difficulties due to social distancing. Furthermore, being self-employed had a positive relationship with COVID-19 stress; in this case, it was prominent in terms of the fear of infection and anger towards others. Since the beginning of the COVID-19 pandemic, Korea has implemented social distancing measures, such as restrictions on the number of private gatherings and limitations in multiuse facilities [28]. According to a survey conducted by the Seoul Metropolitan Government on 526 self-employed individuals from November 20 to December 10, 2021, 93.7% of the participants reported suffering from COVID-19 and 93.7% reported that sales had declined [29]. In 2021, according to data from the Small Enterprise and Market Service, an average of 20,000 individuals had closed their shops or kiosks every month [30]. An August 2021 research by the Korea Development Institute revealed that the total debt within the self-employed sector increased by 21% year-on-year [31]. In this context, it is believed that the extent of the decrease in income and whether they were engaged in self-employment affected individuals’ level of COVID-19-related stress. The results of our study were consistent with those of previous studies. According to Rodríguez et al. [32], low income or economic instability is associated with stress during the COVID-19 pandemic. Shevlin et al. [33] found that low income or a decrease in income was related to depression and anxiety during the COVID-19 pandemic, which can lead to stress caused by COVID-19.

Further, we found that having religion was associated with reduced COVID-19 stress, especially in terms of anger towards others. Ellison and George [34] reported that enhancing emotional and tangible support during a stressful event through religious activities helps buffer the effects of stress. Religious commitment purportedly helps control stress or plays an immunomodulatory role in regulating hormones such as cortisol, which is associated with stress and depression [35,36]. The influence of religious factors on COVID-19 stress in this study can be considered in the same context.

We found that having a graduate degree or higher education was associated with a reduction in COVID-19 stress, especially in terms of the difficulties of social distancing and anger towards others. According to a study that analyzed the differences in risk perception, knowledge, and protective behavior regarding COVID-19 by educational level, high levels of education and knowledge correlated with good adherence to protective behaviors such as hand hygiene and social distancing [37,38]. A low level of education was associated with a greater perceived severity of COVID-19, which can lead to COVID-19-related stress during the pandemic [37]. Considering the results of these preceding studies, participants with a high level of education in this study might have experienced relatively less stress based on up-to-date and more accurate health information, and good adherence to precautionary measures.

Among the four types of marital status (“single,” “married and living with spouse,” “divorced,” and “separated by death”), living with one’s spouse after marriage exhibited a positive correlation with stress caused by COVID-19, especially in terms of the difficulties associated with social distancing. Living alone (among the residence status options) was related to less stress from COVID-19, especially with respect to the fear of infection. The perceived social support of the participants had a positive relationship with COVID-19 stress, especially in terms of fear of infection and anger towards others. Previous studies have shown that the physical illness of one’s spouse can act as a stressor to oneself [39]. These stressors are estimated to increase the stress of participants living with their spouses during the COVID-19 pandemic. Due to social distancing, facilities such as schools and daycare centers for children or the elderly were closed, which increased the burden of supporting their families [40]. It can be assumed that people living with others experience greater COVID-19-related stress owing to the fear of infection from their roommates. In this context, living alone may be associated with a relatively low level of stress during the pandemic. The perceived social support surveyed in this study consisted of three areas, including friends and significant others, in addition to family members. As face-to-face contact with people other than family members has been restricted during the COVID-19 pandemic, those who perceive high social support from friends and meaningful others may have experienced relatively higher stress.

Finally, the degree of depression and anxiety showed a positive relationship with the stress experienced during the COVID-19 pandemic. These results are consistent with those of previous studies showing that COVID-19 results in stress and various psychological symptoms, including anxiety and depression [33,41,42]. According to a systematic review and meta-analysis conducted by Cénat et al. [43], the pooled prevalence of depression, anxiety, and psychological distress were 15.97%, 15.15%, and 13.29%, respectively. Compared to the WHO study on mental health disorders in the general population, the prevalence of depression in populations affected by COVID-19 is more than three times higher than that in the general population, while it is four times higher for anxiety [43]. Esterwood and Saeed [44] found that emotional responses such as extreme fear and uncertainty became more evident during the pandemic. These responses contributed to increased stress responses, which are particularly pronounced in people with pre-existing mental health problems such as depression and anxiety.

Per our expectations, psychiatric symptoms such as depression, anxiety, insomnia, and socioeconomic profiles, including occupations or changes in income, affected stress during the COVID-19 pandemic. The strength of this study is that we investigated and analyzed various individual factors that are expected to influence the stress and mental health of the public during the COVID-19 pandemic, not limited to examining statistical figures. By investigating experiences related to COVID-19, such as of infection, transmission, self-quarantine, and changes in income during the pandemic, we attempted to identify the impact of this special situation on the public. We highlighted the differences between groups with different characteristics and identified both protective and risk factors by analyzing various sociodemographic characteristics and psychosocial scales. We expect the results of this study to be used for screening high-risk groups that are expected to be more susceptible to stress from public health crises. Moreover, it may be helpful to relieve stress and improve people’s mental health by providing individualized psychological interventions and determining appropriate psychiatric services according to their own characteristics, rather than a one-size-fits-all approach. By appropriately allocating limited resources, it will be possible to effectively manage the mental health problems in the general population, which can continue even after the COVID-19 pandemic. Furthermore, the design and results of our study can be used to plan and conduct new research in the event of a public health crisis. We also expect that the results of this study can be used to establish policies related to public health crises.

Nevertheless, our study had several limitations. Although the Bucheon City Mental Health Welfare Center randomly sent the message containing the survey to people, there is possibility that the enrolled subjects may not fully represent the entire population. Therefore, these points should be considered when generalizing our research results and applying them to the entire population of Bucheon or Korea. Among our study participants, the number of those who experienced COVID-19 infection and transmission to others was low. It can be estimated that those who have experienced these experiences might have experienced relatively greater stress; however, we have not sufficiently enrolled these people. As we targeted participants who were able to respond voluntarily due to the study design, people with serious health problems were not included. Regarding the age of the participants, the participants were limited to those in their 20s and 60s, excluding children and the elderly. Lastly, since this study had a cross-sectional design and was conducted for one month, changes in participants’ stress and mental health over time were not reflected. Therefore, if a similar study is conducted, a longitudinal study involving a wider variety of participants is recommended.

In conclusion, suffering from insomnia, female sex, experiencing a large decline in income during the pandemic, being self-employed, and having high levels of depression and anxiety are likely to heighten stress from COVID-19. Being married and living with a spouse, having roommates, and high levels of perceived social support were also associated with higher levels of stress. As we identified various factors that affect the stress and mental health of the general population during the COVID-19 pandemic, we expect that our findings will help improve the mental health of the public during the pandemic.