Abstract
BACKGROUND: Multiple chemical sensitivity (MCS) lacks definitive biomarkers, making differential diagnosis reliant on exclusion and symptom reproducibility. In automobile repair shops, volatile organic compounds (VOCs) from cleaning agents pose risks not only to primary users but also to co-workers via indirect exposure. We report a case of MCS suspected to be triggered solely by bystander VOC exposure, highlighting the clinical significance of uncaptured peak exposures in Korea. CASE PRESENTATION: A 23-year-old mechanic experienced recurrent headaches, throat irritation, and nausea immediately after co-workers used aerosolized cleaners in a poorly ventilated workspace. Symptoms consistently improved when he was away from work. Routine clinical evaluations were unremarkable. Although the patient underwent surgery for chronic rhinosinusitis, the symptoms persisted specifically upon re-exposure, effectively ruling out structural otorhinolaryngologic causes. Mental health screening indicated only mild depressive symptoms, insufficient to account for the severity of the physical symptoms. The Quick Environmental Exposure and Sensitivity Inventory (QEESI) scores were in the "suggestive" range for MCS. While routine workplace monitoring (8-hour time-weighted average [TWA]) showed non-detectable solvent levels, the nature of aerosol application suggested uncaptured short-term peak exposures. Based on the distinct temporal relationship, the patient was placed under medical observation and assessed as fit for work with restrictions on solvent exposure. CONCLUSIONS: This case highlights the role of indirect VOC exposure as a trigger for MCS symptoms even when routine TWA monitoring indicates minimal concentrations. The discrepancy likely stems from the brief peak exposures triggering central sensitization, underscoring the limitations of standard monitoring. Management strategies must focus on peak-exposure control and fitness-for-work assessments that mandate strict avoidance of organic solvents, regardless of average ambient concentrations.