Commentary: the oxygen effect as a possible contributing factor to the mechanism for FLASH protection of normal tissue.

This commentary will review the discovery of the 'Oxygen Effect', discuss problems associated with original and alternative models, and summarize a radiation-chemistry-based model that is relevant to interest in dose-modification. The radiation chemistry background to this model shows directly how radiation depletes oxygen (and other molecules) and that while this depletion is a part of the oxygen effect, it does not define it. Finally, the impact of a shift in half-maximal resistance on radiation protection by FLASH will be illustrated.