Radiation dermatitis (RD) is a common side effect in patients receiving radiotherapy. Currently, clinical skincare approaches for acute RD vary widely among institutions and lack consensus. Hydrogen molecules, acting as radioprotective agents by selectively scavenging free radicals, have the potential to protect against RD. In this study, we demonstrate that hydrogen reduces double-strand breaks, mitochondrial depolarization, and inflammatory cytokines induced by irradiation damage in HaCaT cells. Furthermore, in vivo experiments reveal that exposing irradiated skin areas to a hydrogen gas environment alleviates RD. Assessment of skin appearance grade and histology staining revealed that direct transdermal application of hydrogen can prevent radiation-induced follicle damage, dermal thickening, and leukocyte infiltration, thereby reducing the severity of RD. In addition, hydrogen enhances the skin’s antioxidant capacity, leading to a reduction in the Bcl-2-associated X protein/B-cell lymphoma 2 (Bax/Bcl-2) ratio, the number of apoptotic cells, and the expression of pro-inflammatory cytokines. Our data demonstrate that hydrogen possesses antioxidant, anti-inflammatory, and anti-apoptotic properties, and could be a preventive strategy for RD.