For example, patients with uremic pruritus often experience changes in skin physiology, such as dehydration (xerosis), which leads to dermatologic itching ( 70). Different subtypes of itch conditions might involve common pruriceptive factors. It should be noted that the classification of chronic itch is based on clinical relevance, not on underlying mechanisms. Psychogenic itch is attributed to psychological or psychiatric disorders, such as obsessive-compulsive disorders and delusions of parasitosis. Neuropathic itch results from nerve injury and can arise from diseases or disorders of the central nervous system (CNS) or peripheral nervous system, such as neuropathy, multiple sclerosis, brain tumors, and nerve compression or irritation. The examples of systemic itch include cholestatic pruritus and uremic pruritus. Systemic itch, by contrast, always accompanies diseases of organs other than the skin. Dermatologic itch arises from diseases of the skin, such as atopic dermatitis, eczema, psoriasis, urticaria, and xerosis. On the basis of clinical classification, chronic itch conditions can be divided into four subtypes: dermatologic, systemic, neuropathic, and psychogenic ( 15, 153). Chronic itch, however, remains a challenge in the clinic.

Acute itch evoked by insect bites can be easily relieved by scratching. Itch manifests in both acute and chronic forms. Itch, also known as pruritus, was defined 350 years ago by the German physician Samuel Hafenreffer as an “unpleasant sensation that elicits the desire or reflex to scratch” ( 54, p.

Written on His Skin by Simone Stark