PP-31-011 Background/Aims: It is well documented that the environmental factors, such as air pollutions, volatile organic compounds (VOCs), and suspended bacteria and molds, are important for the development of atopic disease and for triggering atopic symptoms. But there are not enough universal results, which verify the relations. The low allergen room is aimed to minimize the environmental factors that could aggravate the atopic dermatitis. It is designed to remove inhalant allergens, dust, and micro-organisms, which could cause allergic symptoms, and minimize exposure to indoor air pollutants such as VOCs and formaldehyde. The purpose of this study was to verify if improvement in indoor environment can relieve the clinical manifestations of atopic dermatitis and to find the relationship between indoor environment and severity of atopic dermatitis. Methods: A total of 35 children (mean age, 24.3 months) with severe atopic dermatitis (Severity Scoring of Atopic Dermatitis [SCORAD] > 15) and 21 children from a day-care center without atopic dermatitis (mean age, 37.4 months) were recruited. Patients with severe atopic dermatitis were admitted in the low allergen room for 3–4 days (mean, 3.32 days) to see whether clinical symptoms were improved by temporary changing the patient's residential environment while maintaining the regular medical treatment. Severity was assessed using the SCORAD. We compared residential environment in their homes with environment of the low allergen room by measuring indoor air pollutants. Dust, formaldehyde, VOCs (benzene, toluene, ethyl-benzene, xylene, and styrene), carbon monoxide, carbon dioxide, nitrogen dioxide, ozone, suspended fungi, and bacteria were analyzed. Results: SCORAD score was reduced from 44.3 ± 10.9 to 33.2 ± 8.5 by hospitalization in low allergen room. Wilcoxon Signed-Rank test showed significant improvements of symptom scores in patients with atopic dermatitis (P < 0.001) and suspended fungi (P = 0.010) was significantly high in residential environment compared to the low allergen room. Conclusion: The change in residential environment is likely to improve clinical symptoms of atopic dermatitis. It is presumed that particulate matter, formaldehyde, suspended bacteria, and suspended fungi could aggravate atopic dermatitis, but it is too early to conclude that particulate matter, formaldehyde, suspended bacteria, and suspended fungi act as aggravating factors in atopic dermatitis. Further studies are needed for clarifying the relationship between indoor environment and the severity of atopic dermatitis.