Granular parakeratosis

A 40-year-old man presented with symmetrical erythema and desquamation in intertriginous areas accompanied by mild itching for 3 months. Physical examination revealed symmetrical annular erythema and papules with scaling at the posterior neck, axillae, groin, antecubital fossae and popliteal fossae (Figure 1). The patient had previously been diagnosed with atopic dermatitis and treated with topical corticosteroids but experienced minimal improvement and recurring flare-ups. Skin biopsy showed hyperkeratosis, mild epidermal hyperplasia with blurred interface, and infiltration of neutrophils, lymphocytes and plasma cells around the superficial dermal vessels. A detailed medical history revealed that the patient had started using a benzalkonium chloride-based laundry disinfectant 4 months prior. Based on the contact history and clinical presentation, granular parakeratosis (GP) was diagnosed, a rare condition with an incidence of approximately 0.005%, which has become more common with the increased use of benzalkonium chloride during the COVID-19 pandemic. The histopathological features of GP are diverse, with the early stage often presenting as non-specific. While the pathogenesis remains unclear, common triggers include benzalkonium chloride, zinc oxide and antiperspirants. This study was supported by the National Natural Science Foundation of China (82373490). All authors declare no conflict of interest. The authors declare that the procedures followed were in accordance with the ethical standards of Xinhua Hospital affiliated to Shanghai Jiaotong University School of Medicine (XHEC-D-2022-003) and with the 1975 Helsinki Declaration, as revised in 1983. The patient in this manuscript has given written informed consent to the publication of their case details. The data that support the findings of this study are available from the corresponding author upon reasonable request.