Clinical Characteristics of Granular Parakeratosis Caused by Benzalkonium Chloride: A Retrospective Case Series.

Background: Granular parakeratosis (GP) is a rare keratinization disorder. Recent studies have suggested a possible association with exogenous irritants such as benzalkonium chloride (BAK); however, the clinical features of related cases have not yet been systematically characterized. Aim: To analyze the clinical features, histopathological findings, and treatment outcomes of patients with GP induced by BAK exposure, with the aim of enhancing clinical recognition and management of this etiological subtype of GP. Methods: A single-center retrospective study was conducted on eight patients diagnosed with BAK-associated GP confirmed both clinically and histopathologically, who presented between June 2024 and June 2025. Demographic data, clinical manifestations, histopathological changes, and treatment outcomes were collected and analyzed. Results: Among the eight patients, six were male, with ages ranging from 4 to 43 years; four were children. Lesions were primarily distributed over the groin, trunk, neck, and upper chest, all presenting as erythematous-brown patches with characteristic parchment-like scaling. Histopathological examination in all cases revealed parakeratosis and retention of basophilic granules within the stratum corneum. Following definitive diagnosis and cessation of BAK exposure, combined with the use of emollients, complete resolution of lesions was achieved within 2 weeks to 1 month. Conclusion: BAK can induce GP, which presents with certain characteristic features, notably the presence of parchment-like scaling that serves as a valuable clue for differential diagnosis. Early identification and elimination of the causative irritant are key to effective treatment. Pediatric patients may be more susceptible, and the development of GP may be related to individual predisposition and cumulative BAK exposure, warranting further investigation.