Abstract
Oxidative stress is now recognized as a major factor that links metabolic disruption, cell damage, aging, and long-term disease. Reactive oxygen and nitrogen species (ROS/RNS) are normally involved in routine cell signaling, such as immune responses, cell growth, blood vessel control, and metabolic regulation. These molecules become harmful when their levels rise beyond what antioxidant defenses can manage. When this occurs, they gradually damage lipids, proteins, and DNA, disrupt organelle activity, and contribute to cell malfunction. In the past decade, and particularly from 2021 to 2025, research has grown rapidly in areas such as redox signaling, mitochondrial function, environmental sources of oxidative stress, and potential antioxidant treatments. This review brings together established knowledge and recent findings, covering the chemistry of ROS/RNS, their internal and external sources, their molecular effects, the body’s antioxidant defense systems, links to disease, current biomarkers, and developing therapeutic strategies.