Interleukin 31 (IL-31) is a neurocytokine that stimulates sensory neurons involved in pruritus. It contributes to skin barrier inflammation, dysfunction, and remodeling. As the immune and nervous systems are interrelated, IL-31 has a key role in the treatment of atopic dermatitis (AD) and prurigo nodularis (PN). Nemolizumab is a humanized monoclonal antibody that blocks the α subunit of the IL-31 receptor, modulates the neuroimmune response, and rapidly alleviates itching by directly blocking signaling. It reduces inflammation and lesion severity in AD and PN by restoring epithelial function and promoting skin barrier integrity. This review synthesizes the latest information on the functions of IL-31 and presents the current evidence, including clinical trial results, on the use of nemolizumab in the treatment of AD and PN.