Vitamin D, a hormone synthesized in the skin through ultraviolet B radiation (UVB), plays a crucial role not only in calcium and phosphate homeostasis but also in regulating skin homeostasis and modulating immune responses. In keratinocytes, vitamin D is converted to its active form, 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D), which interacts with the vitamin D receptor (VDR) to regulate gene expression involved in proliferation, differentiation, and antimicrobial defense. Dysregulation of this pathway has been implicated in inflammatory skin diseases such as psoriasis, atopic dermatitis, acne vulgaris, and hidradenitis suppurativa. These conditions are associated with altered epidermal differentiation, immune imbalance, and microbial interactions, where vitamin D plays a modulatory role by suppressing proinflammatory cytokines, enhancing antimicrobial peptide synthesis, and restoring skin barrier integrity. Topical vitamin D analogues have shown therapeutic benefits in psoriasis, while emerging evidence supports the adjunctive role of vitamin D supplementation in acne, hidradenitis suppurativa, and atopic dermatitis. Despite promising associations between low serum vitamin D levels and disease severity, a causal relationship remains uncertain. This review integrates molecular mechanisms with clinical findings, emphasizing the role of vitamin D in cutaneous physiology and pathology, and highlights the need for further research into targeted supplementation strategies in dermatological disorders.

Frontal fibrosing alopecia (FFA) is a primary lymphocytic cicatricial alopecia characterized by progressive frontotemporal hairline recession, frequently accompanied by eyebrow and body hair loss. Once considered rare, FFA is now recognized as the most common form of scarring alopecia, predominantly affecting postmenopausal women. Although its pathogenesis remains unclear, hormonal, genetic, autoimmune, and environmental factors have been implicated. Among environmental contributors, the potential role of cosmeceuticals has received increasing attention, with particular emphasis on sunscreen and facial moisturizers. Patch testing has identified sensitization to allergens frequently found in these products. However, due to numerous limitations in the existing studies, the association between cosmeceuticals and FFA remains controversial. As the prevalence of FFA continues to rise alongside widespread cosmetic product use, understanding their potential role in disease pathogenesis is essential. Current findings highlight the need for further investigation into environmental triggers.