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How Hyperbaric Oxygen Works: Henry's Law and Dissolved Oxygen

The physics and physiology behind hyperbaric oxygen therapy — how pressure dissolves oxygen into plasma and what that does in the body.

Medically reviewed by Dr. David Greene, MD · July 2026

Hyperbaric oxygen therapy (HBOT) rests on a simple piece of physics with profound biological consequences: put a person in a pressurized chamber breathing pure oxygen, and you can dissolve far more oxygen into their blood than breathing air at sea level ever allows.

The physics: Henry's Law

The amount of a gas that dissolves in a liquid is proportional to the pressure of that gas above it. At normal pressure, hemoglobin in red blood cells is already about 97% saturated — there is little room for more oxygen in the usual carrier. But the blood plasma itself can hold much more if pressure rises. At 2.4 ATA breathing 100% oxygen, dissolved plasma oxygen rises roughly ten- to twentyfold, enough on its own to meet the body's resting needs.

Why dissolved oxygen matters

Red blood cells are large and cannot always reach damaged, swollen, or poorly-perfused tissue. Oxygen dissolved in plasma travels wherever plasma goes — diffusing into tissue that red cells struggle to reach. This is why HBOT helps precisely the tissues that are most oxygen-starved.

The biological cascade

Beyond simply delivering oxygen, repeated sessions trigger lasting changes. HBOT stimulates the growth of new blood vessels, mobilizes stem cells from bone marrow, supports the oxygen-dependent killing power of white blood cells, and modulates inflammation [1]. In chronic diabetic wounds, randomized evidence links this cascade to improved healing [2].

Dose and limits

More is not better. Oxygen at pressure is a drug with a therapeutic window; excessive exposure risks oxygen toxicity, so protocols cap pressure, session length, and total sessions, and use scheduled air breaks.

References

  1. [1] Hyperbaric oxygen: its mechanisms and efficacy — Thom SR (2011), Plastic and Reconstructive Surgery
  2. [2] Hyperbaric oxygen therapy facilitates healing of chronic foot ulcers in patients with diabetes (HODFU study) — Löndahl M, Katzman P, Nilsson A, Hammarlund C (2010), Diabetes Care

Educational content, not medical advice — see our medical disclaimer. Terms in dotted teal link to the glossary.