Food or environmental allergens play a significant pathogenic role in a subgroup of patients with atopic dermatitis (AD) and can trigger eczema flares. This review focuses on when and which diagnostic and allergen-avoidance measures are beneficial. Diagnosis of allergic triggers may be aided by skin-prick tests measuring serum-specific IgE and/or atopy patch tests (APT) based on the patient’s history, and when necessary, oral food challenges (OFC). In a subset of patients, therapeutic measures, such as elimination of the incriminated allergen(s), can lead to marked improvement of AD; this is especially true for food allergens, but can also apply to inhalant allergens.