Reactive Oxygen Species ROS and free radicals

Reactive Oxygen Species ROS and free radicals are related concepts, but there are important distinctions between the two terms.

Difference between ROS and Free Radicals

Reactive Oxygen Species (ROS):

ROS is a general term that encompasses a variety of molecules derived from oxygen that are highly reactive and capable of causing cellular damage. ROS include not only free radicals but also non-radical oxygen species that are involved in oxidative reactions. Examples of ROS include superoxide anion (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (•OH), and singlet oxygen (^1O2).

Free Radicals:

A free radical is a specific type of molecule with an unpaired electron in its outer shell. This unpaired electron makes free radicals highly reactive and prone to participate in chemical reactions in order to stabilize themselves by either gaining or losing an electron. Free radicals can be generated from various sources, including normal metabolic processes, exposure to environmental toxins, and cellular responses like inflammation.

So, the main difference between ROS and free radicals is that ROS is a broader term that includes both free radicals and non-radical reactive oxygen molecules. All free radicals are considered ROS, but not all ROS are free radicals. Non-radical ROS like hydrogen peroxide (H2O2) are not free radicals because they do not possess unpaired electrons.

Both ROS and free radicals can cause cellular damage through a process called oxidative stress. Oxidative stress occurs when the balance between ROS production and the body’s ability to neutralize them with antioxidants is disrupted. This imbalance can lead to damage to lipids, proteins, DNA, and other cellular components, contributing to various diseases and aging processes.

In summary, reactive oxygen species (ROS) is a general term encompassing various oxygen-derived molecules, including both free radicals and non-radical species. Free radicals are a specific type of ROS characterized by having unpaired electrons, which makes them highly reactive and capable of initiating chemical reactions that can lead to oxidative stress and cellular damage.

How Free Radicals are Produced in Body

Free Radicals Production is closely related to inflammation.  Free radicals are highly reactive molecules that are produced in the body as a natural byproduct of various biochemical processes. They play a role in normal physiological functions, such as immune response and cell signaling, but when their levels become excessive, they can lead to oxidative stress and cellular damage. Here’s how free radicals are produced in the body:

Mitochondrial Respiration:

Mitochondria are the energy-producing organelles within cells. During the process of generating energy through oxidative phosphorylation, some oxygen molecules can be incompletely reduced, leading to the formation of free radicals such as superoxide anion (O2-).


Immune cells produce free radicals as part of their defense mechanisms. Neutrophils and macrophages release reactive oxygen species (ROS) to destroy pathogens during the immune response. However, excessive ROS production can lead to tissue damage.

Metabolism of Drugs and Toxins:

The metabolism of certain drugs and environmental toxins in the liver can generate free radicals as a side effect.

UV Radiation and Environmental Factors:

Exposure to ultraviolet (UV) radiation from the sun and environmental pollutants can trigger the formation of free radicals in the skin and other tissues.

Enzymatic Reactions:

Certain enzymes within cells can generate free radicals during their normal catalytic processes. For example, some enzymes involved in detoxification reactions can produce free radicals as intermediates.

Mitochondrial Dysfunction:

Cellular stressors, such as disruptions in mitochondrial function, can lead to the release of ROS, contributing to oxidative stress.

Ionizing Radiation:

High-energy radiation, such as X-rays and gamma rays, can ionize molecules in the body, generating free radicals as a result.

Cellular Signaling:

Free radicals can also play a role in cell signaling pathways. They are involved in transmitting signals related to growth, differentiation, and responses to external stimuli.


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