Purpose of review: Urticaria is a common skin manifestation with many different causes. It is characterized by local or generalized edematous erythema with itching and increased blood flow and vascular permeability. Individual urticaria lesions typically last less than 24 h (usually less than 12 h), but new lesions may appear and resolve sporadically. Since the diagnosis is usually made based on the history and clinical appearance of the lesions, skin biopsy is not necessarily performed, but it is recommended for evaluating patients with refractory eruptions or suspicion of other diseases exhibiting urticaria-like lesions. The histopathological features of urticaria are dermal edema and perivascular and interstitial inflammatory cell infiltration, and there is only minimal change in the epidermis. Cellular infiltrates are composed of lymphocytes, neutrophils, and eosinophils. Recent findings: In our 64 patients with urticaria, severe edema was found in 48 cases (75%) with mixed cellular infiltration in 45 (70%), lymphocytic infiltration in 17 (27%), and neutrophilic infiltration in 2 cases (3%). Perivascular infiltration was found in 35 cases (55%), and the others were classified into the perivascular and interstitial infiltration type. Subcutaneous cellular infiltration has been shown to be associated with poor treatment response. Summary: In this review, we summarize the histopathological findings of urticaria and its differential diagnosis. Evaluation of the histopathological features may provide further insight into the mechanism of urticaria and potentially provide valuable information to develop more effective treatments.
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