###### Abstract  
Antioxidants are indispensable in protecting the skin from oxidative stress caused by environmental factors such as ultraviolet (UV) radiation, pollution, and lifestyle-related influences. This review examines the essential role of antioxidants in modern cosmetology, highlighting their dual functionality as protective agents and active components in skincare formulations. Oxidative stress, primarily driven by an imbalance between reactive oxygen species (ROS) production and the skin's defense mechanisms, accelerates aging processes, damages cellular structures, and compromises skin integrity. Antioxidants, whether natural or synthetic, act by neutralizing ROS, reducing inflammation, and promoting cellular repair, effectively mitigating these harmful effects. This comprehensive analysis synthesizes findings from 280 studies accessed via key databases, including PubMed, Scopus, and ScienceDirect. It investigates the biochemical mechanisms of antioxidant activity, emphasizing compounds such as vitamins (C, E, A), carotenoids, polyphenols, peptides, and minerals, alongside bioactive extracts derived from algae, fungi, lichens, and plants. Carotenoids, including \(\beta\)-carotene, lutein, lycopene, and astaxanthin, demonstrate potent antioxidant activity, making them crucial for photoproduction and anti-aging. Phenolic compounds, such as ferulic acid, resveratrol, hesperidin, and xanthohumol, play a significant role in neutralizing oxidative stress and improving skin health. This review also highlights bioactives from algae, fungi, and lichens. Algae, particularly microalgae like _Haematococcus pluvialis_, known for astaxanthin production, are highlighted for their extraordinary photoprotective and anti-aging properties. Brown algae (_Fucus vesicususus_) and red algae (_Perphyra_) provide polysaccharides and bioactive molecules that enhance hydration and barrier function. Fungi contribute a wealth of antioxidant and anti-inflammatory compounds, including polysaccharides, \(\beta\)-glucans, and enzymes, which support cellular repair and protect against oxidative damage. Lichens, through unique phenolic metabolites, offer potent free-radical-scavenging properties and serve as effective ingredients in formulations targeting environmental stress. Plant-derived antioxidants offer a diverse range of benefits. Plant-derived antioxidants, such as flavonoids, phenolic acids, and carotenoids, further amplify skin resilience, hydration, and repair mechanisms, aligning with the growing demand for nature-inspired solutions in cosmetics. The integration of these diverse natural sources into cosmetic formulations reflects the industry's commitment to sustainability, innovation, and efficacy. By harnessing the synergistic potential of bioactives from algae, fungi, lichens, and plants, modern cosmetology is advancing toward multifunctional, health-conscious, and eco-friendly products. Future research directions include optimizing delivery systems for these bioactives, enhancing their stability and bioavailability, and expanding their applications to meet evolving dermatological challenges.  
**Keywords:** cosmetology; antioxidants; free radicals; reactive oxygen species; oxidative stress