Cutaneous manifestations of COVID‐19 and COVID‐19 vaccination

In December 2019, a new infectious pathogen named severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) was identified in Wuhan, China. Transmitted through respiratory droplets, SARS‐CoV‐2 is the causative pathogen of coronavirus disease 2019 (COVID‐19). Although this new COVID‐19 infection is known to cause primarily interstitial pneumonia and respiratory failure, it is often associated with cutaneous manifestations as well. These manifestations with COVID‐19 can be classified into seven categories: (i) chilblain‐like skin eruption (e.g., COVID toes), (ii) urticaria‐like skin eruption, (iii) maculopapular lesions, (iv) vesicular eruptions, (v) purpura, (vi) livedo reticularis and necrotic lesions, (vii) urticarial vasculitis, and others such as alopecia and herpes zoster. The pathogenesis of skin eruptions can be broadly divided into vasculitic and inflammatory skin eruptions. Various cutaneous adverse reactions have also been observed after COVID‐19 mRNA vaccination. The major cutaneous adverse reactions are type I hypersensitivity (urticaria and anaphylaxis) and type IV hypersensitivity (COVID arm and erythema multiform). Autoimmune‐mediated reactions including bullous pemphigus, vasculitis, vitiligo, and alopecia areata have also been reported. Several cases with chilblain‐like lesions and herpes zoster after COVID‐19 mRNA vaccination have been published. Various skin diseases associated with COVID‐19 and COVID‐19 vaccination have been reported, and the mechanism has been partly elucidated. In the process, for example, some papers have reported that it is not related to COVID‐19 infection, although it was initially called COVID‐toe and considered a COVID‐19‐associated cutaneous eruption. In fact, some COVID‐19‐associated skin reactions are indistinguishable from drug eruptions. In the future, the mechanisms of COVID‐19‐ or COVID‐19 vaccine‐associated skin reactions need to be elucidated and verification of causal relationships is required.