Hyperbaric Oxygen Therapy and Mild Hyperbaric Oxygen Therapy Are Not Synonymous: A Narrative Review.

Background/Objectives: Hyperbaric oxygen therapy (HBOT) and mild hyperbaric oxygen therapy (mHBOT) are two terms commonly used by hyperbaric chamber sellers, hyperbaric oxygen therapy practitioners, and even by many scientists as if they were synonymous. The following review of hyperbaric oxygen therapy goes into the relevant aspects that relate to the clinical uses of mHBOT and HBOT, such as pressure, the percentage of oxygen in inspired gas, the amount of oxygen dissolved in plasma, and biological effects, as they apply to a broad range of diseases that can be treated with mHBOT and HBOT. Methods: PubMed was searched from January 1990 to March 2026 using combinations of the following example terms: "hyperbaric oxygen therapy," "hyperbaric oxygen," "mild hyperbaric oxygen," and "mild hyperbaric therapy." Additional articles were identified through a reference list review and consensus documents from UHMS, ECHM, EUBS, and ANZHMG. Articles were selected based on relevance to pressure classification, oxygen delivery parameters, physiological mechanisms, clinical outcomes, and terminology standardization. Results: The use of inconsistent terminology for hyperbaric systems has become a serious problem, particularly because low-pressure soft-chamber systems are called "HBOT" but have very different mechanisms of action and even different regulatory requirements. Conclusions: HBOT and mHBOT are not equivalent medical interventions. A set of classification criteria for the proper characterization of pressure, oxygen, and chamber should be formulated. The issues of terminology overlap should be addressed, and how this overlap affects our perception of research data, patients' expectations, clinician-church communication, reimbursement issues, and scientific criteria for experimental design will be discussed.