Intradermal vaccination delivers antigen into the space between the epidermis and the dermis. This space is an anatomically favorable site for immune stimulation, enriched in a heterogenous population of dendritic cells, macrophages, and monocytes that endow this tissue with a potent capacity to detect and respond robustly to immunologic stimuli, including those present in vaccines. For these reasons, the role of the dermis in adaptive immunity has been exploited for allergen testing and tuberculosis skin testing. And smallpox vaccination was developed by Jenner using something similar to intradermal administration: variolation, or the practice of scratching immunizing material into the skin.