Social Vulnerability, Wildfire Exposure, and Mental Health.

Importance: Wildfires are projected to increase in frequency and severity, yet their mental health consequences, particularly the social factors associated with vulnerability, are not well understood. Objectives: To estimate the association between wildfire exposure and psychological distress and to assess the social factors that modify this association. Design, Setting, and Participants: In this longitudinal survey study, a probability-based internet panel of Los Angeles County residents in California was surveyed monthly, before and after the January 2025 wildfires, generating prefire measures of social vulnerability, postfire measures of wildfire impact, and prefire and postfire mental health assessments. Exposure: Residence in an evacuation warning or order zone during the January 2025 wildfires, based on respondents' residential census tracts. Main Outcomes and Measures: Psychological distress was measured monthly using the validated 4-item Patient Health Questionnaire (PHQ-4; range, 0-12, with higher scores indicating greater distress); subscales assessed anxiety and depression. Two-way fixed-effects (TWFE) models with respondent and month-year fixed effects were used to estimate wildfire-associated mental health changes. Results: The analytic sample included 1510 adults (mean [SD] age, 47.2 [15.5] years; 924 [61.2%] female) and 31 632 respondent-month observations spanning October 1, 2023, through December 31, 2025; at wildfire onset, 143 (9.5%) were residing in an evacuation order or warning zone. TWFE models interacting wildfire onset with evacuation zone residence indicated that evacuation zone residents experienced a 0.28-point greater increase in PHQ-4 score (β [SE] = 0.28 [0.09]; P = .002) after wildfire onset. This association showed no significant attenuation over the 11-month follow-up and was concentrated among individuals with household incomes below $100 000, extreme housing cost burden, prefire psychological distress, or limited instrumental social support. Subscale analyses suggest that the increase in PHQ-4 scores was associated primarily with increases in anxiety; after wildfire onset, evacuation zone residents exhibited greater increases in both anxiety (β [SE] = 0.17 [0.05]; P = .002) and depression (β [SE] = 0.12 [0.05]; P = .02), but only anxiety increased significantly from its prefire baseline. Conclusions and Relevance: In this longitudinal survey study of Los Angeles County residents, residential exposure to the January 2025 wildfires was associated with increased psychological distress, but only among individuals with preexisting psychosocial or economic vulnerabilities. Policies that strengthen housing security and instrumental support networks may reduce wildfire-related mental health burdens.