The article reviews the toxic effects of oxygen and the role of oxygen radicals, transition metals, and their interactions in various diseases. Oxygen has long been known to damage living organisms, with even 21% oxygen in the air causing slow but significant damage. The formation of oxygen radicals, particularly superoxide and hydroxyl radicals, is a key mechanism behind these toxic effects. Superoxide radicals are produced by the oxidation of molecular oxygen and can be detoxified by superoxide dismutase (SOD). However, superoxide can react with hydrogen peroxide (H₂O₂) in the presence of transition metals like iron and copper to form highly reactive hydroxyl radicals, which can damage biological molecules. The article discusses the role of iron in generating hydroxyl radicals through the Fenton reaction, where iron reduces superoxide to hydrogen peroxide, which then reacts with iron to form hydroxyl radicals. This process is catalyzed by transition metals and can lead to significant cellular damage. The formation of hydroxyl radicals is implicated in various diseases, including iron overload, rheumatoid arthritis, and cancer. Iron overload, often due to excessive dietary intake or genetic disorders, leads to the accumulation of iron in organs like the liver, spleen, and heart, causing damage through lipid peroxidation and the formation of hydroxyl radicals. Rheumatoid arthritis, an autoimmune disease, is associated with abnormal activation of phagocytes, leading to the production of oxygen radicals and subsequent tissue damage. Cancer, particularly chronic inflammation-driven cancers, also involves changes in body iron distribution, with iron accumulation in certain tissues and loss from the blood, potentially contributing to tumor growth. The article concludes by highlighting the importance of understanding the interactions between oxygen radicals, transition metals, and their role in various diseases to develop effective therapeutic strategies.The article reviews the toxic effects of oxygen and the role of oxygen radicals, transition metals, and their interactions in various diseases. Oxygen has long been known to damage living organisms, with even 21% oxygen in the air causing slow but significant damage. The formation of oxygen radicals, particularly superoxide and hydroxyl radicals, is a key mechanism behind these toxic effects. Superoxide radicals are produced by the oxidation of molecular oxygen and can be detoxified by superoxide dismutase (SOD). However, superoxide can react with hydrogen peroxide (H₂O₂) in the presence of transition metals like iron and copper to form highly reactive hydroxyl radicals, which can damage biological molecules. The article discusses the role of iron in generating hydroxyl radicals through the Fenton reaction, where iron reduces superoxide to hydrogen peroxide, which then reacts with iron to form hydroxyl radicals. This process is catalyzed by transition metals and can lead to significant cellular damage. The formation of hydroxyl radicals is implicated in various diseases, including iron overload, rheumatoid arthritis, and cancer. Iron overload, often due to excessive dietary intake or genetic disorders, leads to the accumulation of iron in organs like the liver, spleen, and heart, causing damage through lipid peroxidation and the formation of hydroxyl radicals. Rheumatoid arthritis, an autoimmune disease, is associated with abnormal activation of phagocytes, leading to the production of oxygen radicals and subsequent tissue damage. Cancer, particularly chronic inflammation-driven cancers, also involves changes in body iron distribution, with iron accumulation in certain tissues and loss from the blood, potentially contributing to tumor growth. The article concludes by highlighting the importance of understanding the interactions between oxygen radicals, transition metals, and their role in various diseases to develop effective therapeutic strategies.