Reactive oxygen species (ROS) are essential for normal physiological processes and play a crucial role in both health and disease. While high levels of ROS can cause damage to proteins, lipids, and nucleic acids, moderate levels regulate cell signaling and are involved in processes such as redox regulation, ion channel function, and transcription factor activity. ROS are also required for biosynthetic processes like thyroid hormone production and extracellular matrix crosslinking. ROS are generated by various sources, including NADPH oxidases (NOX), and are degraded by antioxidant systems. ROS-related diseases can result from either a deficiency or excess of ROS. Antioxidant supplementation has proven largely ineffective in clinical studies, suggesting that their action is too late, too little, or too non-specific. Specific inhibition of ROS-producing enzymes is a more promising approach for clinical efficacy. ROS are involved in immune function, particularly in microbial killing and inflammation resolution. Deficiencies in ROS production, such as in chronic granulomatous disease (CGD), lead to immunodeficiency and recurrent infections. ROS also play a role in thyroid function, as hydrogen peroxide is necessary for thyroperoxidase activity. In cognitive function, ROS are involved in neuronal apoptosis and signaling, and deficiencies in ROS production are associated with cognitive impairments. ROS contribute to various diseases, including cancer, cardiovascular disease, and neurodegenerative disorders. ROS are involved in DNA damage, which can lead to mutations and cancer progression. In cardiovascular disease, ROS contribute to hypertension and vascular dysfunction. In neurological diseases, ROS are involved in neuroinflammation and neurodegeneration, such as in Alzheimer's and Parkinson's diseases. ROS are also implicated in sensory impairment and psychiatric diseases. Antioxidant supplements have not been effective in preventing disease, suggesting that they are too late, too little, or too non-specific. Inhibitors of ROS production, particularly NOX enzymes, are a promising therapeutic approach. NOX inhibitors can be designed to target specific ROS-generating systems, offering a more specific and effective treatment. However, first-generation NOX inhibitors are non-specific and toxic, while newer compounds are more specific and have fewer side effects. Overall, understanding the role of ROS in health and disease is crucial for developing targeted therapies and individualized medicine approaches.Reactive oxygen species (ROS) are essential for normal physiological processes and play a crucial role in both health and disease. While high levels of ROS can cause damage to proteins, lipids, and nucleic acids, moderate levels regulate cell signaling and are involved in processes such as redox regulation, ion channel function, and transcription factor activity. ROS are also required for biosynthetic processes like thyroid hormone production and extracellular matrix crosslinking. ROS are generated by various sources, including NADPH oxidases (NOX), and are degraded by antioxidant systems. ROS-related diseases can result from either a deficiency or excess of ROS. Antioxidant supplementation has proven largely ineffective in clinical studies, suggesting that their action is too late, too little, or too non-specific. Specific inhibition of ROS-producing enzymes is a more promising approach for clinical efficacy. ROS are involved in immune function, particularly in microbial killing and inflammation resolution. Deficiencies in ROS production, such as in chronic granulomatous disease (CGD), lead to immunodeficiency and recurrent infections. ROS also play a role in thyroid function, as hydrogen peroxide is necessary for thyroperoxidase activity. In cognitive function, ROS are involved in neuronal apoptosis and signaling, and deficiencies in ROS production are associated with cognitive impairments. ROS contribute to various diseases, including cancer, cardiovascular disease, and neurodegenerative disorders. ROS are involved in DNA damage, which can lead to mutations and cancer progression. In cardiovascular disease, ROS contribute to hypertension and vascular dysfunction. In neurological diseases, ROS are involved in neuroinflammation and neurodegeneration, such as in Alzheimer's and Parkinson's diseases. ROS are also implicated in sensory impairment and psychiatric diseases. Antioxidant supplements have not been effective in preventing disease, suggesting that they are too late, too little, or too non-specific. Inhibitors of ROS production, particularly NOX enzymes, are a promising therapeutic approach. NOX inhibitors can be designed to target specific ROS-generating systems, offering a more specific and effective treatment. However, first-generation NOX inhibitors are non-specific and toxic, while newer compounds are more specific and have fewer side effects. Overall, understanding the role of ROS in health and disease is crucial for developing targeted therapies and individualized medicine approaches.