What are reactive oxygen species? (with photos)

Ozone is considered a reactive oxygen species.

Reactive oxygen species (ROS) are molecules that contain the element oxygen and are chemically very active. These molecules, which can take many forms, achieve this reactivity due to a common characteristic: the presence of an electron that has only one single bond. Electrons in this state have a strong tendency to try to form stronger bonds, leading to chemical reactions. Reactive oxygen species can be as simple as superoxide molecules (O 2 – ) or more complex molecules such as hydrogen peroxide (H 2 O 2 2 ). These molecules, sometimes called oxidants or free radicals, are found within the human body and are utilized and formed by cellular processes.

Cigarette smoke contains large amounts of reactive oxygen species.

Cells in the human body use superoxide molecules in their conversion of food into energy and other metabolic functions. These biochemical processes are very complex, but many of them start with superoxide molecules being converted into other reactive oxygen species, which are then used in other reactions. The body has natural ways to deal with these molecules, as numerous enzymes have the purpose of neutralizing them or converting them into a less reactive form. An overabundance of reactive oxygen molecules is potentially harmful and is believed to contribute to many processes destructive to human cells, DNA, and eventually to overall health. Many foods and other supplements are marketed as containing antioxidants, which are substances that neutralize excess reactive oxygen species molecules, preventing them from causing damage to the body.

Molecules such as reactive oxygen species can be introduced into the body in a variety of ways, but they are introduced primarily through the air we breathe. Cigarette smoke and industrial exhaust contain large amounts of these types of molecules, which are known to be harmful to human tissues, particularly the lungs. Ozone (O 3 , a naturally occurring molecule, is also very reactive chemically, although it is only present in small amounts in the Earth’s atmosphere.

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Reactive oxygen species can damage human DNA by reacting with proteins contained in DNA strands. This damage can sometimes be repaired by the body’s natural defenses, but these defenses are imperfect, and when repairs fail, the damage can lead to genetic mutations. Oxidative DNA damage can cause reduced enzyme activity and has been linked to cancer. This potential for damage to the body’s cells and tissues, due to the excess of some reactive oxygen species in combination with the need for a certain number of some ROS molecules, creates something of a paradox. The body needs and uses some types of these molecules for basic metabolic functions, but an excess can be harmful.

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