Despite decades of progress in tobacco control, smoking cessation success rates remain stubbornly low. Even with optimal pharmacological and behavioral interventions, sustained abstinence is achieved by a minority of individuals attempting to quit. This commentary advances the thirdhand smoke exposure nicotine ? relapse hypothesis, proposing that residual tobacco smoke pollution in indoor environments represents an overlooked, modifiable determinant of nicotine relapse risk. Thirdhand smoke (THS), the persistent chemical residue of tobacco smoke that accumulates on surfaces, dust, and personal belongings, contains substantial nicotine reservoirs and emits a characteristic stale tobacco odor long after active smoking has ceased. We argue that THS undermine cessation through three interacting pathways: [1] biological re-exposure to nicotine via inhalation, dermal absorption, and ingestion; [2] psychological conditioning through olfactory cues that provoke craving and withdrawal-related distress; and [3] social and structural factors that disproportionately burden populations already at elevated risk for nicotine relapse. Emerging empirical evidence suggests that higher household THS contamination predicts shorter abstinence duration following quit attempts. We contend that incorporating environmental remediation of THS into cessation strategies represents a novel approach to improving long-term cessation outcomes. Future research directions and translational implications are discussed.