<p>Reactive oxygen species (ROS) have double-edged effects on skin, serving as signaling molecules at low levels and inducing oxidative damage when overproduced. Synthetic antioxidants are extensively used but often induce skin irritation and provide temporary benefits. Microalgae and cyanobacteria synthesize a large variety of bioactive molecules with high antioxidant activities, such as carotenoids, polysaccharides, phycocyanin, polyphenols, mycosporine-like amino acids (MAAs), and scytonemin. These molecules exhibit multiple modes of actions: direct scavenging of ROS and metal ions, activation of endogenous antioxidant system, and modulation of expression of oxidative enzymes. Moreover, these antioxidants provide additional advantages in combating skin damages by alleviating inflammation, inhibiting matrix metalloproteinases (MMPs), suppressing tyrosinase to inhibit hyperpigmentation, and enhancing skin hydration and repair. These ingredients are commercially available in moisturizers, anti-aging cosmetics, sunscreens, and therapeutic formulations. However, challenges still exist in large-scale production, extraction methods, bioavailability, biosafety, and rigorous clinical validation. In conclusion, microalgae and cyanobacteria are a promising resource of multifunctional antioxidants that can meet the modern cosmetic needs as well as the “clean beauty” concept. Further studies should focus on technological inventions in processing and delivery systems, and large-scale clinical trials to fully harvest their potential in dermatology and cosmetics.</p>