Yoyo, two years old, has suffered from systemic atopic dermatitis since he was 6 months old. It is found that the times of his acute attack coincide with the high concentration periods of PM 2.5. The rise of aerosol concentration in the air stimulated Yoyo’s fragile and sensitive skin, causing uncontrollable symptoms and repeated outbreaks. Long Hou-ling, attending physician at the Pediatrics Department of the Yangming Branch of Taipei City Hospital, expresses that the causes of atopic dermatitis comprise a genetic allergic constitution and environmental allergen stimulation. In recent years, the latest studies around the world have found that the defect of the natural skin barrier is also an important cause. Young children with atopic dermatitis have congenital defects in their skin lipid composition filaggrin and ceramide and thus cannot withstand external stimulation. When the concentration of PM 2.5 and other air pollutants in the environment rises, the exposure to damaged skin will allow such aerosols to react directly with the immune cells in the dermis layer, causing an inflammatory reaction and severe itching. Therefore, Dr. Long Hou-ling suggests that pregnant women and young children with an allergic constitution shall stay indoors as much as possible, close doors and windows and turn on an air filter with high-efficiency particulate arrestance (HEPA) during days when PM 2.5 concentration is high. Avoid roads with busy traffic and wear face masks when it is necessary to go out. Wash as soon as possible after returning home, change into clean clothes and moisturize the skin immediately. Young children with atopic dermatitis require frequent skin care in their daily life, such as using nourishing lotion containing ceramide and without fragrances, coloring or other chemicals. Children with more serious skin conditions can apply the skin moisturizer more frequently, wear 100% cotton clothes, wipe their sweat with a wet handkerchief immediately after sweating and change into dry and clean clothes when possible. Seek medical attention as soon as possible in case of acute attack and apply drugs locally or orally under the directions of a physician to avoid deterioration of the symptoms.