itching

Itching, or pruritus, is an unpleasant sensation that provokes the urge to scratch. It is a symptom rather than a disease and can affect any part of the body. It may be brief (acute) or persistent (chronic), lasting more than six weeks in the latter case.

Causes of itching are diverse and are often categorized as dermatologic, systemic, neuropathic, or psychogenic. Dermatologic causes include dry skin, eczema (atopic dermatitis), psoriasis, contact dermatitis, fungal infections, and insect bites. Systemic causes encompass iron deficiency, chronic kidney disease–associated pruritus, liver or biliary disease (cholestasis), thyroid disorders, diabetes, and various cancers. Medications such as opioids, some antibiotics, diuretics, and antihypertensives can induce itching. Itching may also occur during pregnancy or without an identifiable rash (pruritus sine materia). Neuropathic itch arises from nerve injuries or disorders, while psychogenic itch is linked to psychological factors.

Pathophysiology involves itch-sensing nerve fibers in the skin (primarily unmyelinated C-fibers) and complex central processing. Histamine release can contribute, but many cases involve histamine-independent pathways and immune mediators. Skin barrier disruption and chronic inflammation can perpetuate itch, and chronic itch may involve ongoing nerve sensitization.

Evaluation starts with a careful history and physical examination to identify distribution, onset, duration, exposure, and associated symptoms. Red flags include unexplained weight loss, night sweats, widespread persistent itch in older adults, or a new rash with systemic symptoms. Basic laboratory testing (eg, blood count, liver and kidney function, thyroid tests) may be used, with further tests guided by findings.

Management focuses on treating the underlying cause and relieving symptoms. General measures include regular emollients, avoiding irritants, gentle cleansing, and keeping nails short. Pharmacologic options include non-sedating antihistamines for mild itch and topical therapies (steroids or calcineurin inhibitors) for inflammatory skin conditions. For chronic or refractory itch, gabapentinoids or certain antidepressants may help. Phototherapy is an option for selected cases, and systemic treatment should address the underlying disease or involve specialists as needed.