Itch is a common symptom of AD which provokes the scratching of the skin causing defective epidermal barrier which leads to the entry of allergens/irritants; eventually the allergen stimulates the release of chemokines (CCL17/TARC and CCL22/MDC) and alarmins (IL-25, IL-33 and TSLP). This evidence concerns the gene CCL17 and Alzheimer disease.