PATHOPHYSIOLOGY OF ITCHING

Itching is the predominant symptom of skin disease but it is ill-under stood and a challenge for future research. Even the major nerve pathwa ys for itch, and its relationship to pain are debatable. In inflamed s kin, histamine plays a major role and its mode of release from mast ce lls in, for example, chronic urticaria is now better appreciated. Tach ykinins including substance P and cytokines including interleukin-2 ar e evidently important peripherally. Opioid mu-receptor-dependent proce sses activate inhibitory circuits in the central nervous system and re gulate the extent of intensity and quality of perceived itch. It is pr oposed that stimulation of large areas of skin such as by scratching, generates inhibitory activity which suppresses itch excitation. Therap eutic intervention based upon understanding these regulatory processes is a real prospect.