Key Factors in the Complex and Coordinated Network of Skin Keratinization: Their Significance and Involvement in Common Skin Conditions.

The epidermis serves many vital roles, including protecting the body from external influences and healing eventual injuries. It is maintained by an incredibly complex and perfectly coordinated keratinization process. In this process, desquamation is essential for the differentiation of epidermal basal progenitor cells into enucleated corneocytes, which subsequently desquamate through programmed death. Numerous factors control keratinocyte differentiation: epidermal growth factor, transforming growth factor-α, keratinocyte growth factor, interleukins IL-1-ß and IL-6, elevated vitamin A levels, and changes in Ca2+ concentration. The backbone of the keratinocyte transformation process from mitotically active basal cells into fully differentiated, enucleated corneocytes is the expression of specific proteins and the creation of a Ca2+ and pH gradient at precise locations within the epidermis. Skin keratinization disorders (histologically characterized predominantly by dyskeratosis, parakeratosis, and hyperkeratosis) may be categorized into three groups: defects in the α-helical rod pattern, defects outside the α-helical rod domain, and disorders of keratin-associated proteins. Understanding the process of keratinization is essential for the pathogenesis of many dermatological diseases because improper desquamation and epidermopoiesis/keratinization (due to genetic mutations of factors or due to immune pathological processes) can lead to various conditions (ichthyoses, palmoplantar keratodermas, psoriasis, pityriasis rubra pilaris, epidermolytic hyperkeratosis, and others).

Cutaneous manifestations of the COVID-19 pandemic in schoolchildren and adolescents.

This review article focuses on cutaneous manifestations in schoolchildren and adolescents 6 to 18 years old connected with various aspects of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, including personal protective equipment (PPE), SARS-CoV-2 infection, and the SARS-CoV-2 vaccine. The use of PPE has been associated with mask-related acne due to microbiome dysbiosis and disruption of skin homeostasis, leading to the emergence of new acne or exacerbation of preexisting acne. Chilblain-like lesions, erythema multiforme-like eruptions, and cutaneous manifestations of multisystem inflammatory syndrome related to SARS-CoV-2 are the most commonly described skin manifestations of SARS-CoV-2 infection. The proposed mechanisms involve either the direct interaction of the virus with the skin through cutaneous receptor angiotensin-converting enzyme 2 in the epidermal basal layer or hyperactive immune responses. The impact of SARS-CoV-2 infection has also been described on adnexa, including hair changes such as alopecia areata and telogen effluvium, as well as nail changes presenting as onychomadesis and periungual desquamation. Cutaneous adverse effects of the SARS-CoV-2 vaccine have been described in case reports and differ from those in adults. Therefore, there is a need for increased awareness regarding the most prevalent cutaneous manifestations associated with COVID-19 in children because they tend to be mild or nonspecific in nature.