摘要：Low fertility has persisted in Japan for decades. Sexless marriages may indirectly contribute to low fertility. Inactive sexual lives within intimate and committed relationships may be linked to sexual activity outside such relationships, called “casual sex”. This study aimed to explore the correlates of casual sex and sexlessness. A web-based questionnaire survey was conducted among married and single men (n = 4000) aged 20–54 years in Japan. Sexlessness were reported by 56% of men, whereas 11% had had casual sex and 31% had had non-casual sex (with spouse, fiancé, or girlfriends/boyfriends) in the last month. Among married men, higher income and long working hours were positively associated with casual sex. Regarding never-married men: those with lower educational status and without full-time jobs were more likely to report casual sex, those in rural areas were more likely to be sexless than those in urban and suburban areas, and those with depression were more likely to be sexless than those without depression. Matching app use was strongly associated with casual sex among married and never-married men, suggesting that such tools may facilitate sexual activity outside committed and intimate relationships. Sexual behavior is closely linked to one’s social and economic environment and health status.
