In recent decades, there has been a marked surge in the development of marine-by-product-derived ingredients for cosmetic applications, driven by the increasing demand for natural, sustainable, and high-performance formulations. Marine animal by-products, particularly those from fish, crustaceans, and mollusks, represent an abundant yet underutilized source of bioactive compounds with notable potential in cosmeceutical innovation. Generated as waste from the fishery and seafood-processing industries, these materials are rich in valuable bioactives, such as chitosan, collagen, peptides, amino acids, fatty acids, polar lipids, lipid-soluble vitamins, carotenoids, pigments, phenolics, and mineral-based substrates like hydroxyapatite. Marine by-product bioactives can be isolated via several extraction methods, and most importantly, green ones. These compounds exhibit a broad spectrum of skin-health-promoting effects, including antioxidant, anti-aging, anti-inflammatory, antitumor, anti-wrinkle, anti-hyperpigmentation, and wound-healing properties. Moreover, applications extend beyond skincare to include hair, nail, and oral care. The present review provides a comprehensive analysis of bioactives obtained from marine mollusks, crustaceans, and fish by-products, emphasizing modern extraction technologies with a focus on green and sustainable approaches. It further explores their mechanisms of action and documented efficacy in cosmetic formulations. Finally, the review outlines current limitations and offers future perspectives for the industrial valorization of marine by-products in functional and environmentally-conscious cosmetic development.

Vitamin D, also called the “sunshine” vitamin, has gained great attention recently due to the observed high percentage of the worldwide population being deficient in this essential bioactive vitamin. Primarily, vitamin D was known for its important role in bone health. Nevertheless, recent research has shown its importance for the brain, heart, muscles, immune system, and skin health, due to its distinct bio-functionality in almost every tissue in the human body. Therefore, its deficiency has been highly correlated with multiple diseases, including skin and dermatologically associated ones. Moreover, different methodologies are applied to synthesize vitamin D, while the main vitamin D sources in human plasma levels and the factors that can cause adverse modifications are multiple. Further research upon vitamin D has exhibited its notable role against skin diseases, such as psoriasis, atopic dermatitis, vitiligo, acne, and rosacea. In this article, a critical review of the most relevant and significant information regarding the relationship between vitamin D and skin health is thoroughly conducted, while emphasis is given to its potential uses and benefits in several cosmetic applications. Current status, limitations, and future perspectives of such a potent bioactive are also extensively discussed.