Hydrogen peroxide (H₂O₂) is a reactive oxygen species that plays a dual role in cellular biology: it can cause oxidative damage but also acts as a signaling molecule in eukaryotic cells. This review discusses the molecular mechanisms by which H₂O₂ is sensed and how antioxidant enzymes regulate H₂O₂ signaling. H₂O₂ is generated by various stimuli, including cytokines and growth factors, and is involved in regulating processes such as immune cell activation, vascular remodeling, stomatal closure, and root growth. Antioxidant enzymes, such as catalase, glutathione peroxidase, and thioredoxin peroxidase, are critical in detoxifying H₂O₂ and modulating its signaling effects. These enzymes are tightly regulated in terms of localization, expression, and activity, which determines the cellular response to H₂O₂. The sensing of H₂O₂ involves the oxidation of specific cysteine residues in proteins, which can trigger changes in protein activity and signaling pathways. For example, in yeast, the transcription factor Yap1 is oxidized in response to H₂O₂, leading to its nuclear translocation and activation of antioxidant genes. Similarly, in mammals, the thioredoxin peroxidase activity of 2-Cys Prx is regulated by oxidation and deoxidation, which influences signaling pathways such as the JNK and p38 SAPK pathways. The regulation of H₂O₂ signaling is also influenced by the localization of antioxidant enzymes, as their compartmentalization can restrict H₂O₂ to specific cellular compartments. The review highlights the importance of understanding the complex interplay between H₂O₂ sensing, antioxidant enzyme regulation, and signaling pathways. It also discusses the implications of these findings for the development of therapeutic strategies targeting oxidative stress and H₂O₂ signaling in diseases such as cancer, atherosclerosis, and neurodegenerative disorders. The study of H₂O₂ signaling in various organisms, including bacteria, yeast, and mammals, has provided valuable insights into the mechanisms by which cells respond to oxidative stress and how antioxidant enzymes contribute to the regulation of H₂O₂ signaling.Hydrogen peroxide (H₂O₂) is a reactive oxygen species that plays a dual role in cellular biology: it can cause oxidative damage but also acts as a signaling molecule in eukaryotic cells. This review discusses the molecular mechanisms by which H₂O₂ is sensed and how antioxidant enzymes regulate H₂O₂ signaling. H₂O₂ is generated by various stimuli, including cytokines and growth factors, and is involved in regulating processes such as immune cell activation, vascular remodeling, stomatal closure, and root growth. Antioxidant enzymes, such as catalase, glutathione peroxidase, and thioredoxin peroxidase, are critical in detoxifying H₂O₂ and modulating its signaling effects. These enzymes are tightly regulated in terms of localization, expression, and activity, which determines the cellular response to H₂O₂. The sensing of H₂O₂ involves the oxidation of specific cysteine residues in proteins, which can trigger changes in protein activity and signaling pathways. For example, in yeast, the transcription factor Yap1 is oxidized in response to H₂O₂, leading to its nuclear translocation and activation of antioxidant genes. Similarly, in mammals, the thioredoxin peroxidase activity of 2-Cys Prx is regulated by oxidation and deoxidation, which influences signaling pathways such as the JNK and p38 SAPK pathways. The regulation of H₂O₂ signaling is also influenced by the localization of antioxidant enzymes, as their compartmentalization can restrict H₂O₂ to specific cellular compartments. The review highlights the importance of understanding the complex interplay between H₂O₂ sensing, antioxidant enzyme regulation, and signaling pathways. It also discusses the implications of these findings for the development of therapeutic strategies targeting oxidative stress and H₂O₂ signaling in diseases such as cancer, atherosclerosis, and neurodegenerative disorders. The study of H₂O₂ signaling in various organisms, including bacteria, yeast, and mammals, has provided valuable insights into the mechanisms by which cells respond to oxidative stress and how antioxidant enzymes contribute to the regulation of H₂O₂ signaling.