Reactive oxygen species (ROS) are normal byproducts of cellular metabolism but can cause oxidative stress when produced in excess. This stress triggers various biological processes, including apoptosis, necrosis, and autophagy. Cytochrome P450 enzymes (CYP) are significant sources of ROS, transforming toxic metabolites into ROS that can damage cells. Cells have evolved antioxidant systems, including enzymatic antioxidants (e.g., superoxide dismutase, catalase, glutathione peroxidases, thioredoxin) and non-enzymatic antioxidants, to neutralize excess ROS. Overproduction of ROS can lead to diseases such as diabetes, cancer, neurodegeneration, and aging. The article reviews the roles of ROS in cellular processes and the importance of endogenous antioxidant systems and natural antioxidants in preventing oxidative stress. It also discusses the mechanisms by which ROS induce autophagy, apoptosis, and necrosis, and their involvement in various diseases. The article highlights the potential of antioxidants in therapeutic interventions for these conditions.Reactive oxygen species (ROS) are normal byproducts of cellular metabolism but can cause oxidative stress when produced in excess. This stress triggers various biological processes, including apoptosis, necrosis, and autophagy. Cytochrome P450 enzymes (CYP) are significant sources of ROS, transforming toxic metabolites into ROS that can damage cells. Cells have evolved antioxidant systems, including enzymatic antioxidants (e.g., superoxide dismutase, catalase, glutathione peroxidases, thioredoxin) and non-enzymatic antioxidants, to neutralize excess ROS. Overproduction of ROS can lead to diseases such as diabetes, cancer, neurodegeneration, and aging. The article reviews the roles of ROS in cellular processes and the importance of endogenous antioxidant systems and natural antioxidants in preventing oxidative stress. It also discusses the mechanisms by which ROS induce autophagy, apoptosis, and necrosis, and their involvement in various diseases. The article highlights the potential of antioxidants in therapeutic interventions for these conditions.