• Unpleasant yet common sensation that provokes a desire to scratch
  • Chronic if persisting for more than 6 wk (incidence increases with age)
  • Generally accepted to be mediated by unmyelinated C-fibers in upper portion of dermis (distinct from those for pain):
    • Transmitted to dorsal horn of spinal cord
    • Via spinothalamic tract to cerebral cortex
  • Peripheral mediators (e.g., histamine and peptides such as substance P that release histamine) stimulate C-fibers and induce itching
  • Prostaglandins (PGE2, PGH2) lower threshold to pruritus
  • Opiates cause pruritus by acting on central receptors
  • No single pharmacologic agent effectively treats all causes of pruritus
  • “Itch–scratch–itch” cycle:
    • Itching triggers scratching
    • Scratching damages skin and stimulates nerve endings, thereby producing even greater itching


  • Dermatologic causes
  • Neurologic causes: Due to CNS or PNS lesions
  • Psychogenic causes
  • Systemic causes

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