Reactive oxygen species (ROS) and antioxidants are central to redox biology, which underpins aerobic life. Free radicals are not inherently harmful; they play essential roles in biological processes, but excessive levels can cause damage. Antioxidants help neutralize these radicals, preventing harm while allowing beneficial functions. This balance is crucial for life, especially in plants, where redox biology is a key theme. The evolution of aerobic life was driven by the need to manage oxygen toxicity. Oxygen, while essential for energy production, is toxic in excess. The rise of atmospheric oxygen 2.2 billion years ago, due to cyanobacterial photosynthesis, led to the development of antioxidant defenses. These defenses evolved to protect against oxidative damage, enabling the transition to aerobic metabolism and the development of complex multicellular organisms. Oxygen radicals, including superoxide (O₂⁻·), hydroxyl (OH·), and singlet oxygen (¹O₂), are highly reactive and can cause significant damage to cellular components. Antioxidants, such as superoxide dismutase (SOD), catalase, and glutathione peroxidase, help neutralize these radicals. Plants and animals have evolved various antioxidant systems to manage ROS, including scavenging enzymes and metal-binding proteins that prevent Fenton chemistry. Despite antioxidant defenses, oxidative damage is inevitable, contributing to age-related diseases like cancer and neurodegeneration. However, ROS also play beneficial roles, such as in immune defense and signaling pathways. The balance between ROS and antioxidants is tightly regulated, and disruptions can lead to oxidative stress, which is linked to various diseases. Antioxidant supplements are often perceived as beneficial, but the human body maintains a delicate balance, making it difficult for external antioxidants to significantly alter this balance. Thus, while antioxidants are essential, their supplementation does not necessarily extend lifespan or prevent aging-related diseases. Understanding redox biology is crucial for developing strategies to manage oxidative stress and promote health.Reactive oxygen species (ROS) and antioxidants are central to redox biology, which underpins aerobic life. Free radicals are not inherently harmful; they play essential roles in biological processes, but excessive levels can cause damage. Antioxidants help neutralize these radicals, preventing harm while allowing beneficial functions. This balance is crucial for life, especially in plants, where redox biology is a key theme. The evolution of aerobic life was driven by the need to manage oxygen toxicity. Oxygen, while essential for energy production, is toxic in excess. The rise of atmospheric oxygen 2.2 billion years ago, due to cyanobacterial photosynthesis, led to the development of antioxidant defenses. These defenses evolved to protect against oxidative damage, enabling the transition to aerobic metabolism and the development of complex multicellular organisms. Oxygen radicals, including superoxide (O₂⁻·), hydroxyl (OH·), and singlet oxygen (¹O₂), are highly reactive and can cause significant damage to cellular components. Antioxidants, such as superoxide dismutase (SOD), catalase, and glutathione peroxidase, help neutralize these radicals. Plants and animals have evolved various antioxidant systems to manage ROS, including scavenging enzymes and metal-binding proteins that prevent Fenton chemistry. Despite antioxidant defenses, oxidative damage is inevitable, contributing to age-related diseases like cancer and neurodegeneration. However, ROS also play beneficial roles, such as in immune defense and signaling pathways. The balance between ROS and antioxidants is tightly regulated, and disruptions can lead to oxidative stress, which is linked to various diseases. Antioxidant supplements are often perceived as beneficial, but the human body maintains a delicate balance, making it difficult for external antioxidants to significantly alter this balance. Thus, while antioxidants are essential, their supplementation does not necessarily extend lifespan or prevent aging-related diseases. Understanding redox biology is crucial for developing strategies to manage oxidative stress and promote health.