Background <p>While household dysfunction (HD) is associated with negative health outcomes, it remains unclear whether the duration or timing of exposure contribute to aggression. The underlying mechanisms in the HD-aggression relationship are also understudied. This study examined the effects of HD duration and timing on aggression while investigating potential mediating role of depressive symptoms. Sex differences were also explored.</p> Methods <p>Data were obtained from 7,800 participants in the Taiwan Birth Cohort Study (52.32% male, 47.68% female) followed to ages 17 or 18 years. HD were coded at five life stages: infancy, early childhood, middle childhood, late childhood, and early adolescence. A structured life course modeling approach was used to assess whether the accumulation of HD (duration), or the timing of exposure, including exposure during sensitive periods and more recent periods, exhibited the strongest association with aggression at age 17 or 18. Causal mediation analysis was conducted to evaluate the role of depressive symptoms in the pathway from HD to aggression.</p> Results <p>Among males, both HD accumulation (β = 0.04, 95% CI: 0.004–0.07) and middle childhood HD (β = 0.04, 95% CI: 0.01–0.07) were associated with increased adolescent aggression at age 17/18. Depressive symptoms at age 12 mediated the effects of both cumulative HD and middle childhood HD on aggression at ages 17/18, accounting for an estimated 33% and 20% of the total effects, respectively. No significant association between HD and aggression was observed among females.</p> Conclusions <p>Interventions should address HD early and sustain support throughout adolescence, while also targeting depressive symptoms, to effectively reduce aggression, particularly among males.</p>