Mild Hyperbaric Therapy vs Medical HBOT: Key Differences

Mild Hyperbaric Therapy and Medical HBOT Are Not the Same Treatment

Mild hyperbaric therapy (often shortened to mHBOT) usually means lying in a soft, inflatable chamber pressurised with ordinary air to about 1.3 atmospheres absolute (ATA). Medical hyperbaric oxygen therapy (HBOT) means breathing near-100% oxygen in a rigid chamber, at 2.0 ATA or more for the conditions it is accepted for.

The Undersea and Hyperbaric Medical Society (UHMS) states that breathing air at less than 1.4 ATA does not meet the definition of hyperbaric oxygen therapy, and that the soft chambers used for mild hyperbaric therapy are FDA-cleared only for acute mountain sickness.

This guide explains the difference in pressure, oxygen, regulation and evidence, so you know which one a clinic is actually offering.

What Counts as Hyperbaric Oxygen Therapy?

The UHMS defines HBOT as breathing near 100% oxygen while enclosed in a hyperbaric chamber at a pressure equal to or greater than 1.4 ATA. It adds that all UHMS-approved indications currently require near-100% oxygen at a minimum of 2.0 ATA.

In practice, a 2017 review in Advances in Wound Care describes typical clinical treatment pressures as 2 to 3 ATA. Treatment happens in one of two chamber types:

• Monoplace chambers hold one person. The whole chamber is usually filled with oxygen.
• Multiplace chambers hold several people. The room is pressurised with air and patients breathe oxygen through a mask or hood, often with a staff member inside.

What Is Mild Hyperbaric Therapy?

Mild hyperbaric therapy is delivered mostly in portable fabric chambers. The UHMS position statement describes them as operating at less than 1.4 ATA and designed to be pressurised only with air.

The FDA's 510(k) summary for one such device, the Flexi-Lite chamber (K051759), shows what these devices are cleared for:

• It is described as a "mild hyperbaric chamber for pressures less than 5 psi", with relief valves set at 4 psi. Four psi above sea-level pressure works out to roughly 1.3 ATA.
• It is pressurised with atmospheric air from a compressor.
• Its indicated use is "to provide mild hyperbaria for the treatment of Acute Mountain Sickness (AMS) and its associated mild symptoms."
• It is a prescription device: federal law restricts its sale to "by or on the order of a physician."

The FDA's consumer guidance on HBOT says the same about this category of device. It describes a zippered bag cleared to treat altitude sickness only, notes that the FDA has not cleared these bags for use with oxygen tanks or oxygen concentrators, and warns that using them as homemade HBOT devices can pose a risk of fire and suffocation.

Mild pressures are not limited to soft chambers. The UHMS notes that mild hyperbaric therapy is also offered in clinical hard-shell chambers. The chamber type alone does not tell you the dose, so always ask what pressure and what gas a session uses.

How Much Oxygen Does Each One Deliver?

The amount of oxygen that dissolves in your blood depends on the pressure of the oxygen you breathe. You can estimate that pressure by multiplying the oxygen fraction of the gas by the chamber pressure. Air is 21% oxygen, according to the FDA.

On this simple calculation, a medical session at 2.4 ATA exposes you to roughly nine times the oxygen pressure of a mild session on air. The UHMS puts it more bluntly: mild hyperbaric exposure with air delivers no more oxygen to the body than breathing oxygen by mask at normal sea-level pressure.

Side-by-Side Comparison

For a broader look at the two chamber designs, see our hard-shell vs soft-shell chamber guide.

What Does the Research Say?

Medical HBOT

As of July 2021, the FDA listed the conditions hyperbaric chambers are cleared for. They include air or gas bubbles in blood vessels, carbon monoxide poisoning, crush injury, decompression sickness, gas gangrene, sudden hearing loss, severe skin and bone infections, radiation injury, skin grafts or flaps at risk, sudden vision loss from blocked blood flow, and non-healing diabetic foot ulcers. Our HBOT indications list compares the UHMS, European and Medicare lists.

Some of these rest on randomised trials. In one double-blind trial of 152 patients with carbon monoxide poisoning, three hyperbaric oxygen sessions within 24 hours cut the rate of cognitive problems at six weeks from 46.1% to 25.0%. HBOT for other uses, such as brain injury or long COVID, is still investigational.

Mild hyperbaric therapy

The UHMS position statement says: "We are not aware of any reliable clinical evidence that mild compression to less than 1.4 ATA has any therapeutic effect." The society does not recommend mild hyperbaric therapy for any medical purpose other than acute mountain sickness.

Some researchers have used mildly pressurised air as a control group. In a 2001 randomised trial in The Lancet, 111 children with cerebral palsy received 40 sessions of either 100% oxygen at 1.75 ATA or air at 1.3 ATA. Both groups improved on every outcome, with no difference between them: gross motor scores rose 2.9% with oxygen and 3.0% with pressurised air. Ear problems were more common in the oxygen group (27 children) than the air group (15 children).

That result is sometimes cited as proof that 1.3 ATA works. The trial was not designed to test that, and it had no group without any chamber sessions, so it cannot separate a pressure effect from the effects of attention, routine or natural development. The investigators concluded only that the improvement in both groups deserves further study.

Which One Fits Your Situation?

Look for medical HBOT if:

• You have a condition on the FDA or UHMS list, such as a non-healing diabetic foot ulcer or radiation tissue injury.
• A physician has referred you for hyperbaric oxygen treatment.
• You want the pressures and oxygen levels that were actually tested in clinical trials.

Emergencies are different. For suspected carbon monoxide poisoning or decompression illness, call your local emergency number first. Emergency hyperbaric treatment happens in hospital chambers. Divers can also call the DAN Emergency Hotline on +1-919-684-9111 after contacting emergency services.

Mild hyperbaric therapy may appeal if:

• Your interest is general relaxation or wellness rather than treating a diagnosed condition.
• You accept that professional bodies do not consider it hyperbaric oxygen therapy and that evidence of benefit is lacking.
• You will use the chamber as designed, with air only, and never add an oxygen concentrator.

What about 1.5 ATA sessions?

Some clinics run hard-shell chambers at around 1.5 ATA. With near-100% oxygen, that meets the UHMS pressure threshold for HBOT (1.4 ATA). It is still below the 2.0 ATA minimum used for every UHMS-approved indication, so ask the clinic what evidence supports that pressure for your goal.

Questions to Ask Any Provider

1. What pressure does your chamber reach during my session, in ATA?
2. Will I breathe air, or near-100% oxygen, and how is it delivered?
3. Is the chamber FDA-cleared (or CE-marked in Europe), and for which uses?
4. Is a physician involved in my assessment and supervision?
5. What evidence supports this pressure and number of sessions for my condition?
6. Is the facility accredited, for example by the UHMS?

Our guide on how to choose an HBOT clinic covers accreditation and staff credentials in more detail, and HBOT side effects explains the risks.

Finding the Right Clinic

If you are comparing chamber types before buying or booking, read soft shell vs hard shell hyperbaric chambers. To see providers close to you, use find HBOT clinics near me and check each listing for chamber type and pressure.

Sources

• Undersea and Hyperbaric Medical Society, UHMS Position Statement: Low-Pressure Fabric Hyperbaric Chambers (created 2017, revised 2018). Also published as UHMS Position Statement in full: low-pressure fabric hyperbaric chambers. Undersea Hyperb Med. 2018;45(4):486-487.
• U.S. Food and Drug Administration, 510(k) summary K051759: Flexi-Lite Hyperbaric Chamber (2005).
• U.S. Food and Drug Administration, Hyperbaric Oxygen Therapy: Get the Facts (consumer update, content current as of July 2021; archived copy).
• Heyboer M 3rd, Sharma D, Santiago W, McCulloch N. Hyperbaric Oxygen Therapy: Side Effects Defined and Quantified. Adv Wound Care. 2017;6(6):210-224.
• Undersea and Hyperbaric Medical Society, Ten Guidelines for Patients and Referring Physicians in Selecting Safe Hyperbaric Oxygen Treatments (April 2025).
• Weaver LK, Hopkins RO, Chan KJ, et al. Hyperbaric oxygen for acute carbon monoxide poisoning. N Engl J Med. 2002;347(14):1057-1067.
• Collet JP, Vanasse M, Marois P, et al. Hyperbaric oxygen for children with cerebral palsy: a randomised multicentre trial. Lancet. 2001;357(9256):582-586.
• Divers Alert Network, Emergency Assistance

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Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. The choice between medical HBOT and mild hyperbaric therapy should be made with a qualified healthcare professional. Neither should replace conventional medical treatment for serious conditions.