The Oxygen Effect refers to the discovery (made in 1921) that living cells are significantly more damaged by radiation (X-ray, particle beams etc) in the presence of oxygen.

It's currently of particular significance to radiologists, who want to preserve cells undamaged (e.g.during medical X-rays) - or, when deliberately trying to damage cells in tumour radiation etc. The presence of oxygen can increase the rate of damage by up to 300%.

There are several theories which attempt to explain the effect - but no general agreement as yet.

The best known explanation of the oxygen effect is the oxygen fixation hypothesis developed by Alexander in 1962, which posited that radiation-induced non-restorable or "fixed" nuclear DNA lesions are lethal to cells in the presence of diatomic oxygen. Recent hypotheses include one based on oxygen-enhanced damage from first principles.. Another hypothesis posits that ionizing radiation provokes mitochondria to produce reactive oxygen (and nitrogen species), which are leakage during oxidative phosphorylation that varies with a hyperbolic saturation relationship observed with both the oxygen and nitric oxide effects

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