It is estimated that one in 10 young adults (aged 18–24 years) experience homelessness in the United States each year [1]. Compared to their housed counterparts, these young adults report higher rates of risky sexual behaviors (including trading sex for shelter), substance use, and poor physical and mental health [[2], [3], [4], [5], [6]]. Within this population, evidence suggests that longer durations of homelessness and more frequent episodes of homelessness may contribute to worse health outcomes [[7], [8], [9]]. For example, studies have found that compared to newly homeless young adults, those homeless for > 6 months were more likely to use drugs intravenously, engage in sex work, have at least four sexual partners, and report worse physical and mental health [10,11]. A study of homeless adolescents found that for each additional year of age, there was a 37% reduction in the likelihood of exiting [10]. In addition to duration, research on adults highlights the unique burdens facing those with multiple episodes of homelessness, whose “episodic” experiences may be associated with destabilizing transitions between homelessness, carceral systems, institutions, or unsafe residential arrangements [12]. Furthermore, the chances of exiting homelessness in later life may decrease with longer duration and more frequent episodes of young adult homelessness [13,14].
The purpose of this study is to examine the impact of duration and number of homelessness episodes on health outcomes for unsheltered homeless young adults, which refers to those living on the street, in cars, abandoned buildings, and other places not meant for human habitation. Research suggests that unsheltered homelessness versus sheltered homelessness contributes to worse health outcomes [8,15], yet few studies have specifically focused on unsheltered young adults. Our lack of understanding of health risks facing unsheltered young adults limits our ability to address health needs and set priorities for homelessness prevention and early intervention. Furthermore, the relationship between health and homelessness in young adults experiencing unsheltered homelessness is not fully understood; in particular, whether increased duration and frequency of homelessness leads to worse health outcomes, or whether youth with health challenges are at an increased risk of becoming homeless.
While we hypothesize that rates of physical health conditions, mental health conditions, and substance use disorder will be highest among unsheltered young adults with longer durations and more frequent episodes of homelessness, for this study, duration and frequency of homelessness were combined and operationalized as homeless trajectory groups based on previous work demonstrating differential experiences and health outcomes of homelessness by trajectory [[16], [17], [18]]. Specifically, unsheltered young adults were classified into three homeless trajectory groups: (1) short-term–homeless less than a year and one time, (2) episodic–homeless less than one year and more than one time, and (3) long-term–homeless more than or equal to one year. While we expect that rates of physical health conditions, mental health conditions, and substance use disorder will be highest among unsheltered youth experiencing episodic and long-term homelessness, we further test whether these differences can be explained by observable differences in the sociodemographic background and structural burdens characterizing individual case histories, or whether differences by trajectory persist even in the presence of statistical controls for case history.