Itch Neuro-Immune Circuits in Atopic Dermatitis: From the Itch-Scratch-Inflammation Feed-Forward Loop to Counter-Regulatory Negative Feedback

Itch and inflammation in atopic dermatitis (AD) have long been read as two parallel outputs of a single disease process. That framing sits awkwardly with the anatomy. Cutaneous sensory neurons and immune cells sit side by side in the skin and speak a shared language of ligand-receptor pairs. We recast that interface here as a bidirectional regulatory network, not a one-way road running from inflammation to itch. Going in one direction, type 2 and innate cytokines act straight on sensory neurons as pruritogens, each through its own receptor and signalling route. Going the other way, neuron-derived mediators such as substance P, VIP and NGF reshape how immune cells are recruited, polarized and how tissue is remodelled. Put together, the two arms form a feed-forward loop. Scratching, barrier disruption, cutaneous dysbiosis and central sensitization all feed one another. Within this framework, several counter-regulatory mechanisms have also been identified, including the capacity of CGRP to restrain type 2 immunity and the immunomodulatory functions of IL-31 that extend beyond its pruritogenic role. What the circuit does, then, hinges on how the work is split among sensory neuron subsets and on the state of each node, rather than on any linear cascade. Seen through this lens, today's and tomorrow's therapies-dupilumab, tralokinumab, nemolizumab, JAK inhibitors and kappa-opioid agonists-each land on a specific node of the circuit. The picture helps make sense of treatment-resistant itch and argues for rational, combination targeting of the circuit.