Oxidative stress occurs when there is an imbalance between oxidants and antioxidants, favoring oxidants. Reactive oxygen species (ROS), such as superoxide anion, hydroxyl radical, and hydrogen peroxide, are produced by normal cellular metabolism and environmental factors like air pollutants and cigarette smoke. These ROS can damage cellular components like carbohydrates, nucleic acids, lipids, and proteins, leading to various diseases, including cancer, neurological disorders, atherosclerosis, hypertension, ischemia/perfusion, diabetes, acute respiratory distress syndrome, idiopathic pulmonary fibrosis, chronic obstructive pulmonary disease, and asthma. Aerobic organisms have antioxidant systems, including enzymatic and non-enzymatic antioxidants, to neutralize ROS. However, in pathological conditions, these systems can be overwhelmed, increasing oxidative stress. ROS are generated from molecular oxygen through various pathways, including the Haber-Weiss and Fenton reactions, which produce hydroxyl radicals. These radicals can damage DNA, proteins, and lipids, leading to cellular dysfunction. Exogenous sources of oxidants include cigarette smoke, ozone exposure, hyperoxia, ionizing radiation, and heavy metal ions. These factors can increase ROS production and damage cellular components. Antioxidants, both enzymatic and non-enzymatic, help counteract oxidative stress. Enzymatic antioxidants include superoxide dismutase (SOD), catalase, and glutathione peroxidase (GSH-Px), while non-enzymatic antioxidants include vitamins C and E, beta-carotene, and glutathione (GSH). These antioxidants protect cells by scavenging ROS, reducing oxidative damage, and maintaining redox balance. Oxidative stress can lead to DNA damage, lipid peroxidation, and protein oxidation, which can result in genetic mutations, cellular dysfunction, and disease. It also affects signal transduction pathways, leading to inflammation and other cellular responses. The balance between oxidants and antioxidants is crucial for maintaining cellular function, and disruptions in this balance can contribute to various pathological conditions. Understanding the mechanisms of oxidative stress and the role of antioxidants is essential for developing strategies to prevent and treat oxidative-related diseases.Oxidative stress occurs when there is an imbalance between oxidants and antioxidants, favoring oxidants. Reactive oxygen species (ROS), such as superoxide anion, hydroxyl radical, and hydrogen peroxide, are produced by normal cellular metabolism and environmental factors like air pollutants and cigarette smoke. These ROS can damage cellular components like carbohydrates, nucleic acids, lipids, and proteins, leading to various diseases, including cancer, neurological disorders, atherosclerosis, hypertension, ischemia/perfusion, diabetes, acute respiratory distress syndrome, idiopathic pulmonary fibrosis, chronic obstructive pulmonary disease, and asthma. Aerobic organisms have antioxidant systems, including enzymatic and non-enzymatic antioxidants, to neutralize ROS. However, in pathological conditions, these systems can be overwhelmed, increasing oxidative stress. ROS are generated from molecular oxygen through various pathways, including the Haber-Weiss and Fenton reactions, which produce hydroxyl radicals. These radicals can damage DNA, proteins, and lipids, leading to cellular dysfunction. Exogenous sources of oxidants include cigarette smoke, ozone exposure, hyperoxia, ionizing radiation, and heavy metal ions. These factors can increase ROS production and damage cellular components. Antioxidants, both enzymatic and non-enzymatic, help counteract oxidative stress. Enzymatic antioxidants include superoxide dismutase (SOD), catalase, and glutathione peroxidase (GSH-Px), while non-enzymatic antioxidants include vitamins C and E, beta-carotene, and glutathione (GSH). These antioxidants protect cells by scavenging ROS, reducing oxidative damage, and maintaining redox balance. Oxidative stress can lead to DNA damage, lipid peroxidation, and protein oxidation, which can result in genetic mutations, cellular dysfunction, and disease. It also affects signal transduction pathways, leading to inflammation and other cellular responses. The balance between oxidants and antioxidants is crucial for maintaining cellular function, and disruptions in this balance can contribute to various pathological conditions. Understanding the mechanisms of oxidative stress and the role of antioxidants is essential for developing strategies to prevent and treat oxidative-related diseases.