Wildfire smoke-related PM2.5 concentration measurements, perceived indoor air quality, and health symptoms among Southern California residents during the 2025 Los Angeles wildfires: A latent class mediation approach

• The 2025 Los Angeles wildland-urban interface fires exposed residents to toxic pollutants. • Los Angeles residents experienced adverse physical and mental health symptoms during the fires. • Indoor air quality is an important measurement when researching wildfire health effects. • Brain fog may be a novel wildfire-related neurological health symptom. Numerous studies have linked wildfire exposure to adverse physical and mental health outcomes and symptoms. However, few studies incorporate both outdoor wildfire smoke-related PM 2.5 concentration and indoor air quality measurements. Understanding the mechanisms by which objectively measured and perceived wildfire smoke impact people’s health could facilitate interventions to mitigate adverse health effects. Survey data were obtained from N = 849 adult residents in the Los Angeles area 2–3 months after the 2025 wildfires. A latent class analysis identified subgroups of people with similar symptom experiences. Associations between wildfire smoke-related PM 2.5 concentration and indoor air quality with likely class membership were examined. We identified three latent subgroups: Physical and Mental Health Symptoms, Physical Health Symptoms, and Low Symptoms. Higher outdoor wildfire smoke-related PM 2.5 levels were associated with a higher likelihood of belonging to the symptomatic classes, and indoor air quality statistically explained most of this association. Indoor exposure may be an important mechanism by which people are exposed to wildfire smoke, which can cause adverse health symptoms. While outdoor PM 2.5 concentration is commonly used in wildfire exposure research, our findings suggest that perceived indoor air quality provides additional explanatory information about who experiences more severe symptom profiles, particularly for wildland-urban interface fires where many residents are sheltering in place.