This study aimed to compare the psychological symptoms of humidifier disinfectant survivors to the general population and explore socio-demographic factors influencing survivors’ psychological symptoms. A one-way Multivariate Analysis of Covariance (MANCOVA) and a series of two-way MANCOVA were conducted with a sample of 228 humidifier disinfectant survivors and 228 controls. The results demonstrated that the survivor group displayed higher anxious/depressed symptoms, withdrawn symptoms, somatic complaints, thought problems, attention problems, aggressive behavior and rule-breaking behavior than the general group. Moreover, among the socio-demographic factors, the two-way interaction effects of group × family economic status and group × number of friends were found to be statistically significant. The limitations and implications of this study are discussed.

This study aimed to examine group differences in the survivors of humidifier damage and the effect of individual psychotherapy on the psychological symptoms of the survivor groups, using the single group pre–post study design. A series of Wilcoxon–Mann–Whitney tests were conducted to investigate the level of psychological problems before and after psychotherapy, as well as the main and interaction effects of demographic characteristics and adaptive functioning on the treatment effects in 69 humidifier disinfectant survivors. The results demonstrated significant differences in problems with socioeconomic status (SES), life functioning, friendships, family relationships, and job adjustment in the survivor groups. Groups with high SES, low life functioning, and poor friend relationships had more problem behaviors than other groups. Problem behaviors related to friendship levels were different before and after psychotherapy. After psychotherapy, individuals with limited social connections exhibited a greater decrease in problem behaviors compared to those with strong friendships. This paper extends the international literature on the long-term consequences of environmental health hazards and the importance of tailored mental health interventions.

Evidence comparing dose-effect and good-enough level (GEL) models is drawn largely from Western outpatient and university counselling samples treating common mental health problems. It therefore remains unclear whether these models generalize to non-Western, post-disaster counselling contexts. This study examines session-by-session outcome trajectories among South Korean survivors of the humidifier disinfectant disaster and tests whether these patterns align with dose-effect and GEL predictions. We analyzed routine outcome monitoring data from humidifier disinfectant disaster survivors in South Korea (180 clients; 2307 sessions; 105 therapists). Outcome Rating Scale (ORS) scores were modelled with multilevel growth curves and compared across aggregate and treatment-length-stratified specifications. A negatively accelerating log-linear trajectory best fit the data, showing rapid early improvement followed by decelerating gains. Stratified models revealed a significant interaction between session progress and treatment length; brief care (≤5 sessions) typically did not reach the ORS clinical cutoff (25) despite exhibiting the steepest initial improvement rate. Reliable and clinically significant change peaked in the 11-20 session group compared to the brief care group, whereas individuals attending more than 20 sessions showed sustained but relatively stabilized recovery pattern. Findings support complementary dose-effect and GEL perspectives, highlighting the inadequacy of rigid session caps for highly distressed survivors. The higher odds of recovery in moderate-to-long-term group (11-20 sessions) emphasize that survivors require a sufficient dose to consolidate gains. These results underscore routine outcome monitoring and flexible care structures as practical tools for dynamically tailoring treatment lengths in national-scale trauma counselling programmes.