Ozone and oxygen
Singlet oxygen / reactive oxygen species (ROS)
Reactive oxygen species are chemically reactive oxygen-containing molecules — superoxide, hydrogen peroxide, the hydroxyl radical and singlet oxygen. Singlet oxygen is ordinary O2 raised to an excited state, not ozone and not a free atom of oxygen. The two terms are often wrongly used as synonyms.
Also called ROS, singlet oxygen, 1O2, reactive oxygen species
The chemistry
Reactive oxygen species (ROS) is an umbrella term for oxygen-derived molecules that react far more readily than ground-state O2: the superoxide anion (O2•−), hydrogen peroxide (H2O2), the hydroxyl radical (•OH) and singlet oxygen.
Singlet oxygen (¹O2) is molecular oxygen in an excited electronic state. It is still two oxygen atoms; what differs is the arrangement of electron spins, which removes the restriction that makes ordinary oxygen sluggish. It is short-lived and highly reactive.
Two of these terms are often used as though they were interchangeable, and they are not:
- Singlet oxygen is not ozone. Ozone is O3.
- Singlet oxygen is not “nascent” or atomic oxygen. A single free oxygen atom is a different species again.
Where ROS come into ozone therapy
On Velio Bocci’s account — the standard mechanistic reference in this field, reviewed in Archives of Medical Research (2006), and developed for blood plasma and extracellular fluid rather than for skin — ozone contacting a moisture film does not travel onward as ozone. It reacts immediately, preferentially with polyunsaturated fatty acids, and is consumed. Bocci describes the products of that reaction, principally hydrogen peroxide and a family of lipid oxidation products, as the actual “ozone messengers” that carry any downstream effect.
What those messengers then do inside the body — signalling, antioxidant enzyme induction, adaptation to repeated mild oxidative stress — is a proposed mechanism, and it belongs with the biology entries.
Why it matters here
These are the words that come up when someone explains what ozone does once it reaches the skin. Knowing that singlet oxygen is neither ozone nor a loose oxygen atom makes the rest of the explanation much easier to follow.