Hyaluronic acid (HA) is a linear, unbranched polysaccharide classified as a glycosaminoglycan. While HA is found in various tissues throughout the body, over half of its total proportion is found in the skin. The role of HA in the skin is complex and multifaceted. HA maintains proper hydration, elasticity, and skin firmness, serving as a key extracellular matrix (ECM) component. With age, HA production gradually decreases, leading to reduced water-binding capacity, drier and less elastic skin, and the formation of wrinkles. Additionally, HA plays an active role in the wound-healing process at every stage. This review summarizes the current background knowledge about the role of HA in skin aging and wound healing. We discuss the latest applications of HA in aging prevention, including anti-aging formulations, nutricosmetics, microneedles, nanoparticles, HA-based fillers, and skin biostimulators. Furthermore, we explore various HA-based dressings used in wound treatment, such as hydrogels, sponges, membranes, and films.

In recent years, interest in the impact of diet on the skin has increased significantly, and dietary interventions are now considered an essential part of managing certain dermatological conditions. Among them, the ketogenic diet (KD) has gained particular attention. KD is a high-fat, very low-carbohydrate, and moderate-protein dietary approach that induces ketosis, defined by serum ketone body concentrations exceeding 0.5 mmol/L. Although initially developed for the treatment of drug-resistant epilepsy in children, its applications have broadened over time. Current evidence on KD and the skin remains limited, focusing mainly on inflammatory skin diseases such as acne, psoriasis, and hidradenitis suppurativa (HS), as well as cutaneous melanoma. In this review, we summarize the existing data on these conditions and discuss the molecular mechanisms underlying the potential effects of KD, including anti-inflammatory and antioxidant pathways, modulation of signaling cascades, and interactions with the gut microbiota. Finally, we also address the reported adverse effects of KD on the skin.