Prurigo nodularis is a chronic condition that is triggered by repetitive rubbing or scratching of discrete areas of the skin. It may alternatively be induced by repetitive picking or rubbing of nonpruritic skin.

Although the exact prevalence is unknown, it is most commonly seen in patients aged 45 years and older and seems to be more common in women. Prurigo nodularis presents as one or more (usually multiple) discrete, severely pruritic nodules that mostly appear on the extensor surfaces of extremities and anterior areas of the thighs and legs. The lesions are rarely seen on the face. Pruritus is described as severe and distressing and can become worse with heat, sweating, or irritation from friction.

Prurigo nodularis may be secondary to skin conditions associated with pruritus, such as atopic dermatitis and xerosis, as well as systemic conditions associated with generalized pruritus without a primary skin rash, such as HIV infection, iron-deficiency anemia, diabetes mellitus (type 1, type 2), gluten enteropathy, thyroid disease, renal or hepatic impairment, malignancies, and others. In most cases, the etiology of pruritus is unknown. Studies have suggested that prurigo nodularis may be a form of subclinical small fiber neuropathy and that Th2 cytokines play an important role in its pathogenesis. In the nonpruritic cases, repetitive picking induces the lesions. In these cases, there may be an underlying psychological component that results in the inability to break the itch-scratch cycle.