Itch

Itch, or pruritus, is an unpleasant sensation that prompts scratching. It is a symptom rather than a disease, with a wide range of causes and durations from short-lived to chronic (lasting more than six weeks).

Mechanism: Itch signals originate in specialized skin nerve fibers, primarily unmyelinated C fibers, and travel to the spinal cord and brain. Mediators such as histamine can trigger itch, especially in dermatitis, but many cases involve non-histaminergic pathways and complex central processing that modulates itch intensity.

Causes: Common skin-related triggers include inflammatory conditions such as atopic dermatitis, contact dermatitis, psoriasis, and dry skin. Systemic diseases can also cause itch, including kidney failure, cholestasis, iron deficiency, and thyroid disorders. Infections (for example, scabies), medications (opioids, gabapentinoids, certain antihypertensives), and pregnancy are additional sources. Itch can be localized or widespread and may occur with or without visible skin rash; neuropathic or central itch is possible without skin disease.

Evaluation: Diagnosis relies on history and physical examination to identify likely causes. Targeted laboratory tests or imaging may assess liver and kidney function, thyroid status, iron levels, and other organ systems as indicated. Itch severity can be assessed with scales such as a numerical rating scale or visual analog scale.

Management: Treatment focuses on addressing the underlying cause when possible. General measures include regular skin moisturization, avoiding irritants, and treating dryness. Topical therapies (emollients, corticosteroids, calcineurin inhibitors) reduce skin inflammation. For symptom relief, sedating antihistamines are sometimes used at night; gabapentinoids or certain antidepressants may help neuropathic itch. Phototherapy and systemic therapies are options for resistant cases. Behavioral strategies and good sleep hygiene can also be beneficial.