The term dermal hypersensitivity reaction (DHR) originated among dermatopathologists to describe a particular histologic reaction pattern seen in a variety of skin disorders. It has been adopted as clinical nomenclature for the diagnosis of a poorly understood but commonly observed skin eruption that carries the same histologic reaction pattern but does not fit any other diagnosis. In this sense, DHR as a clinical diagnosis should be a diagnosis of exclusion.

DHR presents as a pruritic rash characterized by either an urticaria-like morphology or as crusted erythematous papules, similar to arthropod bites. Unlike urticaria, lesions are fixed and last more than 24 hours. Pruritus is often intense and debilitating. Variants of DHR that appear predominantly urticarial have sometimes been labeled as urticarial dermatitis in the literature, whereas the more papular forms have been labeled variably as urticarial papulosis, subacute prurigo, papular dermatitis, and itchy red bump disease. Patients can present with both morphologies simultaneously.

Research into epidemiology, risk factors, and comorbidities is sparse. Patients are typically females in their sixth to seventh decade of life, but any sex and age can be affected. Some studies suggest an association with hematologic and internal malignancy. Medications are known triggers of DHR as well. Although the pathogenesis of DHR is not well understood, the histology can be readily identified as a superficial to mid-dermal perivascular infiltrate of lymphocytes and eosinophils with minimal epidermal change.

The clinical course of DHR is unpredictable. Some patients may experience resolution within a couple years, but DHR is often a chronic, persistent disease.