Antioxidants and Their Effects on Free Radicals Free radicals and reactive oxygen species (ROS) are natural products of cellular metabolism, particularly during cellular respiration and mitochondrial activity. Although these reactive species have important physiological roles, excessive production or insufficient regulation may lead to oxidative stress, which can damage lipids, proteins, and nucleic acids. Antioxidants play an essential role in protecting cells against the harmful effects of reactive species. They include various compounds and enzymes that limit oxidative reactions and help maintain the balance between oxidation and reduction processes within cells. Antioxidants act through several mechanisms, including donating an electron or hydrogen atom to free radicals, thereby reducing their reactivity and limiting their ability to attack cellular components. Some antioxidants can also terminate chain reactions, such as lipid peroxidation, which may affect the integrity of cellular membranes. Al-Mustaqbal University – The First University in Iraq