The prevalence of allergic diseases is increasing gradually. Exposure to allergens is one of the trigger factors for symptoms in sensitized individuals. House dust mites and cockroach are the two most common indoor aeroallergens in Taiwan. There are wide differences in the numbers in different locations and in different seasons of these allergens. Sensitization to food allergens is prominent in young infants and can predict further aeroallergen sensitization. However, whether early exposure to allergens might develop or prevent allergic diseases in later childhood requires further research. Up to the present, allergen avoidance has demonstrated no prominent clinical efficacy in the improvement of allergic symptoms, although it is able to reduce allergen load in the environment. In a clinical regard, allergen avoidance should still be included as a part of treatment plans and be well explained to patients.