Background: As the number of internet users increases, problems related to internet overuse are becoming more and more serious. Adolescents and youth may be particularly attracted to and preoccupied with various online activities. In this study, we investigated the relationship of internet addiction, smartphone addiction, and the risk of hikikomori, severe social withdrawal, in Japanese young adult. Methods: The subjects were 478 college/university students in Japan. They were requested to complete the study questionnaire, which consisted of questions about demographics, internet use, the Internet Addiction Test (IAT), the Smartphone Addiction Scale (SAS)–Short Version (SV), the 25-item Hikikomori Questionnaire (HQ-25), etc. We investigated the difference and correlation of the results between two groups based on the purpose of internet use or the total score of each self-rating scale, such as screened positive or negative for the risk of internet addiction, smartphone addiction, or hikikomori. Results: There was a trend that males favored gaming in their internet use while females used the internet mainly for social networking via smartphone, and the mean SAS-SV score was higher in females. Two-group comparisons between gamers and social media users, according to the main purpose of internet use, showed that gamers used the internet longer and had significantly higher mean IAT and HQ-25 scores. Regarding hikikomori trait, the subjects at high risk for hikikomori on HQ-25 had longer internet usage time and higher scores on both IAT and SAS-SV. Correlation analyses revealed that HQ-25 and IAT scores had a relatively strong relationship, although HQ-25 and SAS-SV had a moderately weak one. Discussion: Internet technology has changed our daily lives dramatically and altered the way we communicate as well. As social media applications are becoming more popular, users are connected more tightly to the internet and their time spent with others in the real world continues to decrease. Males often isolate themselves from the social community in order to engage in online gaming while females use the internet as to not be excluded from their communications online. Mental health providers should be aware of the seriousness of internet addictions and hikikomori.

The word hikikomori, the abnormal avoidance of social contact, has become increasingly well-known. However, a definition of this phenomenon has not been discussed thoroughly. The aim of this study is to gain a better understanding of the perception of hikikomori amongst health-related students and professionals and to explore possible psychiatric conditions underlying hikikomori. A total of 1,038 subjects were requested to complete a questionnaire regarding hikikomori phenomenon. While some differences in the perception of hikikomori do exist, all subjects tended to disagree with the statement, “hikikomori is NOT a disorder”. Regarding the underlying psychiatric disorders of hikikomori, approximately 30% of psychiatrists chose schizophrenia as the most applicable ICD-10 diagnosis for hikikomori, whereas 50% of pediatricians chose neurotic or stress-related disorders. An argument still exists regarding the relationship between hikikomori and psychiatric disorders. We propose that the term hikikomori could be used to describe severe social withdrawal in the setting of a number of psychiatric disorders.

Smartphone use is pervasive among youth in Japan, as with many other countries, and is associated with spending time online and on social media anywhere at any time. This study aimed to test a Japanese version of the Smartphone Addiction Scale-Short Version (SAS-SV) among Japanese college students. The subjects of this study were 602 college students in Japan. The study questionnaire consisted of questions about demographics (age, gender etc.), possession of a smartphone, internet use [length of internet use on weekdays and weekend, favorite social networking service (SNS) etc.], Young's Internet Addiction Test (IAT), and the Smartphone Addiction Scale-Short Version (SAS-SV) translated into Japanese. There was a total of 573 respondents (180 male, 393 female) who completed the questionnaire (mean 19.3±1.3 years). LINE was the most popular social media platform (52.0%) followed by Twitter (36.3%). The overall Internet Addiction Test (IAT) score was 45.3±13.2, with 4.5% classified as having severe addiction (IAT ≥70). The mean SAS-SV scores were 24.4±10.0 for males and 26.8±9.9 for females. Based on proposed cutoff scores, 22.8% of males and 28.0% of females screened positive for smartphone addiction. The total scores of the SAS-SV and the IAT was correlated significantly. As the number of smartphone users becomes higher, problems related to smartphone use also become more serious. Our. suggest that the Japanese version of SAS-SV may assist in early detection of problematic use of smartphones.

Aim: Internet addiction (IA), also referred to as Internet use disorder, is a serious problem all over the world, especially in Asian countries. Severe IA in students may be linked to academic failure, attention‐deficit hyperactivity disorder (ADHD), and forms of social withdrawal, such as hikikomori. In this study, we performed a survey to investigate the relation between IA and ADHD symptoms among college students.Methods: Severity of IA and ADHD traits was assessed by self‐report scales. Subjects were 403 college students (response rate 78%) who completed a questionnaire including Young's Internet Addiction Test (IAT) and the Adult ADHD Self‐Report Scale–V1.1.Results: Out of 403 subjects, 165 were male. The mean age was 18.4 ± 1.2 years, and mean total IAT score was 45.2 ± 12.6. One hundred forty‐eight respondents (36.7%) were average Internet users (IAT < 40), 240 (59.6%) had possible addiction (IAT 40–69), and 15 (3.7%) had severe addiction (IAT ≥ 70). Mean length of Internet use was 4.1 ± 2.8 h/day on weekdays and 5.9 ± 3.7 h/day on the weekend. Females used the Internet mainly for social networking services while males preferred online games. Students with a positive ADHD screen scored significantly higher on the IAT than those negative for ADHD screen (50.2 ± 12.9 vs 43.3 ± 12.0).Conclusion: Our results suggest that Internet misuse may be related to ADHD traits among Japanese youth. Further investigation of the links between IA and ADHD is warranted.