Association of season of birth with personality traits and schizotypy: a systematic review

Season of Birth (SoB) has been hypothesized to influence personality through early developmental exposures such as photoperiod, environmental temperature, and maternal hormones during gestation and neonatal period. This systematic review aimed to synthesize and critically evaluate existing evidence on the association between SoB and personality traits across different theoretical frameworks, psychometric instruments, and populations. This systematic review followed PRISMA 2020 guidelines. Comprehensive searches were conducted in PubMed, Scopus, Web of Science, and PsychINFO from inception to May 2026 using keywords and MeSH terms related to “season” and “personality” or “temperament.” Grey literature was also reviewed. Eligible studies included observational designs assessing personality, temperament, or schizotypy in relation to SoB, using validated psychometric instruments. Risk of bias was assessed via the Newcastle–Ottawa Scale. A narrative synthesis was performed due to methodological heterogeneity. Studies were grouped by theoretical framework (e.g., Big Five, temperament, schizotypy), psychometric tool, and outcome domain. Out of 5,952 identified records, 21 studies ( n = 51,192 participants) met inclusion criteria. Most studies employed cross-sectional designs and used tools like the Temperament and Character Inventory (TCI), Schizotypal Personality Questionnaire (SPQ), and NEO Personality Inventory (NEO-PI). Associations between SoB and personality were most consistent for schizotypy where winter birth was linked to elevated scores. In temperament frameworks, the majority of studies found no significant effects; while some isolated reports noted seasonal associations with Novelty Seeking, Reward Dependence, Persistence, and Cooperativeness, these were inconsistent and often moderated by age and sex. In contrast, models based on the Big Five or Eysenck’s framework showed minimal or inconsistent associations. Effect sizes across studies were small, and findings were often moderated by age, gender, or clinical risk status. While SoB is not a major determinant of personality, it may contribute modestly to individual differences within biologically based models, particularly in temperament and schizotypy research.