Does a microbial-endocrine interplay shape love-associated emotions in humans? A hypothesis

Emerging evidence suggests that the human gut microbiome plays a regulatory role in the endocrine system, influencing hormone activity and potentially shaping the emotional and physiological dimensions of behaviors such as aggression and emotional states, including love. Here, we review the hypothesis that microbial-endocrine interactions shape love-associated emotions by modulating hormone levels and activity. While the division of love into discrete components such as lust, attraction, and attachment is somewhat artificial and may not fully capture the complexity of human experience, the associated emotions nevertheless correspond to well-characterized neuroendocrine processes. Psycho-endocrinological theory proposes that the complex and nonlinear interplay between testosterone, estradiol, and other hormones drives emotions associated with lust; serotonin and dopamine play a role in emotions linked to attraction; and oxytocin and vasopressin influence the modulation of attachment and social bonds. Microbial communities may influence emotions and relationship dynamics through effects on the hormonal pathways linked to love-associated emotions. While non-human animal studies suggest microbiota can impact social bonding, sexual preferences, and stress-related behaviors, direct evidence in humans remains limited. Investigating the evolutionary underpinnings of microbial-endocrine interactions could provide insights into how microbes influence emotions beyond love, including hate and aggression—with important societal implications. Indeed, understanding these mechanisms could have profound implications for human relationships, mental health, and even therapeutic interventions targeting the microbiota-gut-brain axis. Future research is needed to unravel the extent to which microbiomes contribute to the neurobiology of love (and other emotions) and whether manipulating microbial communities could modulate emotional and social behaviors.