Itch, which is defined as an unpleasant sensation of the skin that leads to the desire to scratch, has a profound negative effect on the quality of life of our patients. Although pruritus (itch) is the most frequent symptom in dermatology, it remains a major clinical challenge. Itch can be produced by various inflammatory skin diseases, allergies, tumors, autoimmune diseases, metabolic diseases, neuropathic states, and psychiatric disorders, as well as being a side effect from medications. Optimal treatment is often hampered by our lack of understanding of the pathophysiology, the crucial mediators, and the failure to identify “itch receptors.” Similar to pain, itch is a sensation that derives from activation of the sensory nervous system. Sensory nerve endings in the epidermis and dermis transmit the “itch signal” via the spinal cord and spinalthalamic tract to the central nervous system. The brain also appears to be a major player in the processing and chronicity of itch. Thus, the itch that patients perceive is an integrated perception modulated at 4 levels in the nervous system: first, in the periphery; second, in the dorsal root ganglia; third, at the spinal cord level; and fourth, in the brain. Basic science research has elucidated the levels at which antipruritic agents work and provides potential new targets for drug development. Clinical and basic science research on itch is a fascinating field for new discoveries. Recent discoveries, such as new histamine receptors, histamine-independent itch pathways, including gastrin-releasing peptide, proteases, and cytokines, illustrate that itch research has entered a new era. The development of new drugs, such as calcineurin inhibitors, slow-release local anesthetics, the
-opiate receptor agonists, monoclonal antibodies targeting molecules involved in itch pathophysiology (eg, anti-immunoglobulin E, anti-nerve growth factor, anti-interleukin-4, anti-interleukin-31), substantiate the importance of itch in dermatology. We are delighted that, in this volume, we could bring together many of the key opinion leaders in the fields of basic and clinical “pruritology” to provide state-of-the-art reviews of the neuroanatomy and neurophysiology of peripheral and central itch. These articles are designed to help the practitioner understand the cellular and molecular basis of the itch that afflicts patients with various diseases, including atopic dermatitis and other inflammatory skin diseases, as well as systemic diseases, HIV, and cancer. We hope that this volume, which spans the basic and clinical science of pruritus, from bench to bedside, will give the reader greater insight into the pathogenesis of pruritus, and provides an approach for managing the itch patient in daily clinical practice.