The phrase "HBOT" gets used for two very different things. One is the hospital wound-care protocol at 2.0 to 2.4 ATA in a hard-shell chamber. The other is the wellness protocol at 1.3 ATA in a soft-shell chamber.
The pharmacology, the FDA pathway, and the evidence base are all different.
This guide compares the two head to head. The goal is not to declare one better; it is to make the differences explicit so patients can match the right modality to the right use case.
The biggest fault line: soft-shell 1.3 ATA chambers are sold as "general wellness" devices, not as medical devices. The FDA explicitly distinguishes the two pathways in its 2019 wellness guidance. The marketing often blurs the line.
The pressure difference is physical, not semantic
The shorthand "ATA" stands for atmospheres absolute. Sea level is 1.0 ATA. A medical chamber at 2.4 ATA puts the patient at 2.4 times sea-level pressure. A wellness chamber at 1.3 ATA puts them at 1.3 times.
This is not a trivial difference. The physics matters.
At 1.0 ATA on room air (21% oxygen), arterial PO2 is roughly 100 mmHg. On 100% oxygen at the same pressure, it rises to ~600 mmHg.
At 1.3 ATA on 100% oxygen, arterial PO2 reaches roughly 600 to 800 mmHg (Tibbles & Edelsberg 1996). At 2.4 ATA on 100% oxygen, it reaches ~1500 mmHg.
The 2.4 ATA condition delivers roughly two to three times the arterial oxygen of the 1.3 ATA condition. That is not a small gap. It is the difference between two distinct interventions.
For more background on chamber operating pressures, read our chamber-verification guide.
The FDA pathway difference
Hard-shell chambers are cleared as medical devices under 510(k) product code CBF. The FDA reviews them for pressure safety, oxygen fit, and "substantial equivalence" to prior devices.
Soft-shell 1.3 ATA chambers are typically sold under the general wellness pathway. This pathway, introduced in 2019, allows low-risk products to be sold for "general wellness" use without 510(k) clearance.
The general wellness pathway has a key restriction: the product cannot claim to treat any specific disease. A soft-shell chamber can be marketed for "general wellness" or "recovery." It cannot be marketed for autism, long COVID, traumatic brain injury, or any other named condition.
Some soft-shell manufacturers have pursued 510(k) clearance for their devices. These are the exception. Most soft-shell chambers in the US market operate under general wellness.
The FDA published a 2019 consumer warning calling out clinics that misrepresent soft-shell chambers as medical devices.
The evidence base difference
Medical HBOT at 2.0+ ATA has decades of RCTs behind it for set indications. The Faglia diabetic foot trial 1996, the Marx radiation bone work 1985, and the Weaver CO trial 2002 set the evidence base for the 14 conditions Medicare now covers.
Mild HBOT at 1.3 ATA has a much thinner evidence base. The primary research came out of work in pediatric autism and post-concussion populations in the 2000s and 2010s.
The Rossignol 2009 autism trial reported benefit at 1.3 ATA in 62 children. A subsequent Granpeesheh 2010 trial at the same pressure found no benefit. The American Academy of Pediatrics does not recommend HBOT for autism.
The HOPPS trial 2015 and the BIMA trial 2018 tested HBOT for post-concussion syndrome at 2.0 ATA. Both used hard-shell chambers. Both found no statistical benefit over sham.
The evidence base for 1.3 ATA mild HBOT specifically remains limited. Some downstream effects (gene expression changes, growth-factor release) may still occur at lower pressures. Whether those translate to clinical benefit for any specific condition is not yet established.
The chamber engineering difference
A hard-shell monoplace chamber is a pressure vessel rated for 2.0 to 3.0 ATA operating pressure. It is typically made of steel or acrylic with steel reinforcement. It costs $80,000 to $150,000 new.
Hard-shell chambers have oxygen-compatible interior surfaces (no static-prone fabrics, no flammable materials). They have multiple safety interlocks. They have grounding systems for electrostatic discharge.
A soft-shell chamber is a flexible fabric envelope (typically urethane-coated nylon) rated for 1.3 ATA maximum. It uses an air compressor for pressurization and an oxygen concentrator for breathing gas.
Soft-shell chambers cost $5,000 to $20,000. They are portable. They can be set up in a home office or wellness clinic without specialized facility modification.
The engineering difference reflects the regulatory difference. A 2.4 ATA chamber with 100% oxygen flow is a different engineering problem than a 1.3 ATA chamber with concentrated air. Both are pressure vessels; only one is a medical device.
The safety profile difference
Medical HBOT carries known risks. The most common is ear barotrauma during compression and decompression. Lung oxygen toxicity, CNS oxygen toxicity (seizures), and chamber fires are real but less common (UHMS safety review 2018).
Chamber fires in medical HBOT have killed patients. The most cited cases include the 2009 Lauderhill, FL incident that killed a child and her grandmother. Hospital-grade chambers use rigorous fire-safety controls; soft-shell wellness chambers have different fire profiles.
Mild HBOT at 1.3 ATA has a lower safety risk on most dimensions. Pulmonary oxygen toxicity is rare at 1.3 ATA. CNS oxygen toxicity is essentially absent. Ear barotrauma is still possible but less common because pressure changes are smaller.
That does not mean mild HBOT is risk-free. Soft-shell chambers have caught fire, and the 1.3 ATA pressure change is still real. Patients with claustrophobia, sinus issues, or untreated ear problems can have trouble in either type.
The cost difference
A 40-session protocol at a hospital wound-care center, billed to Medicare for an FDA-approved indication, costs Medicare roughly $25,000 to $30,000. Patient out-of-pocket is the standard Part B copay.
A 40-session protocol at an independent hard-shell clinic, private-pay, runs $10,000 to $20,000.
A 40-session protocol at a soft-shell wellness clinic runs $2,000 to $4,000. Membership models can lower per-session cost further.
The cost difference roughly tracks the chamber cost and the regulatory burden. It does not necessarily track therapeutic value.
For more on session counts and pricing math, read our 40-session protocol explainer.
When mild HBOT may be appropriate
Honest framing. Mild HBOT may have a role for some uses.
Recovery and athletic-performance use. Some athletes use 1.3 ATA sessions for recovery from intense training. The mechanism is unproven but the safety profile is favorable.
Post-procedure mild HBOT for elective surgery patients. Some cosmetic and plastic surgeons recommend 1.3 ATA sessions post-procedure. Evidence is anecdotal.
General wellness experiences for healthy adults curious about HBOT. As a low-risk experience without clinical claims, soft-shell 1.3 ATA can be a reasonable introduction.
What mild HBOT is not appropriate for: any FDA-approved indication. Diabetic foot ulcers, radiation tissue injury, carbon monoxide poisoning, and the other 11 approved conditions all require medical-grade pressure and oversight.
When medical HBOT may be appropriate
For the 14 conditions Medicare covers under CMS LCD L33718 2024, medical HBOT at 2.0+ ATA in a UHMS site is standard care. This list includes diabetic foot ulcer, late radiation injury, stubborn bone infection, decompression sickness, and CO poisoning. See the osteomyelitis evidence atlas for the full study-by-study evidence breakdown.
For off-label uses with strong off-label evidence (such as some forms of crush injury or compromised flap recovery), medical HBOT is also appropriate. The evidence is weaker than for the FDA-approved indications but stronger than for wellness use. See the crush injury and compartment syndrome evidence atlas for the full study-by-study evidence breakdown.
For off-label uses with weak or mixed evidence (long COVID, autism, anti-aging, TBI), medical HBOT may be tried under close oversight. The evidence does not strongly support these uses, and clinics that push them hard are running ahead of the data.
The Aviv Clinics protocol at The Villages uses medical-grade 2.0 ATA chambers for anti-aging and cognitive applications. The chambers are appropriate; the marketing of the indication is what gets controversial. Our Aviv evidence-vs-marketing analysis covers the gap.
The dose-equivalence claim
Some wellness clinics argue that long exposure at 1.3 ATA is "dose-equal" to shorter exposure at 2.4 ATA. The argument goes: 3 sessions a week at 1.3 ATA over 16 weeks equals 5 sessions a week at 2.4 ATA over 8 weeks.
The math does not work that way. Arterial PO2 is the dose-driving variable, and PO2 at 1.3 ATA is roughly one-third of PO2 at 2.4 ATA (Tibbles & Edelsberg 1996). Time at depth does not linearly compensate.
Some cellular effects (gene activity, growth-factor release) may still happen at lower pressures and build up over time. Others — like new vessel growth — appear to need the higher pressure to kick off.
The honest answer: dose-equivalence between 1.3 and 2.4 ATA HBOT has not been established in controlled trials for any specific outcome. Claims of equivalence are mostly marketing.
The "mild" branding problem
The word "mild" carries a specific marketing implication. It suggests a milder, safer version of the same intervention. This framing is misleading.
Mild HBOT is not a less intense version of medical HBOT. It is a different intervention with a different dose, different evidence base, different regulatory pathway, and different clinical role.
A more accurate framing might be "low-pressure HBOT" or "general-wellness HBOT." The "mild" branding came out of the marketing strategy for soft-shell chambers in the 2000s; it has stuck despite being imprecise.
For patients, the practical takeaway: the chamber pressure rating matters. "Mild" tells you nothing precise; "1.3 ATA soft-shell" tells you a lot.
What hospital wound-care physicians say
A useful triangulation. The hospital-based UHM physicians who treat FDA-approved indications generally do not use 1.3 ATA mild HBOT in their practice. The UHMS Indications Manual does not include any indication for 1.3 ATA treatment.
This is partly because the evidence base for 1.3 ATA does not meet the UHMS threshold for indication. It is partly because hospital chambers are not built for low-pressure operation; running a 2.4 ATA-rated chamber at 1.3 ATA is mechanically possible but operationally unusual.
The split is roughly clean: medical HBOT for clinical indications happens at 2.0+ ATA in hospital wound centers. Mild HBOT happens at 1.3 ATA in wellness clinics. There is little crossover in practice.
For more on academic medicine's stance on off-label HBOT, see our institutional silence analysis.
Bottom line
Medical HBOT and mild HBOT are different interventions. They use different chambers, different pressures, different evidence bases, and different FDA pathways. Both are sold as "HBOT," but the term is doing too much work.
For FDA-approved indications, choose medical HBOT at 2.0+ ATA in a UHMS-accredited facility. For off-label uses with strong evidence, medical HBOT is also appropriate. For wellness or recovery use without clinical claims, soft-shell 1.3 ATA may be a reasonable low-risk option.
What the two should not be is interchangeable. A clinic that markets 1.3 ATA soft-shell sessions as equivalent to hospital wound-care HBOT is misrepresenting the pharmacology and the regulatory category.
If a clinic uses the word "mild" without specifying chamber pressure and shell type, ask the clarifying question. The answer will tell you which intervention you are buying.
Related Reading
- How to verify a clinic's chamber is medical-grade
- FDA-cleared hyperbaric chambers complete list
- UHMS-accredited HBOT facilities: what certification means
- The 40-session HBOT protocol explained
- Aviv Clinics: evidence vs marketing
Frequently asked questions
Is 1.3 ATA actually hyperbaric?
Yes, technically. Hyperbaric means "above atmospheric pressure." 1.3 ATA is above 1.0 ATA, so the term applies. The clinical meaning of "hyperbaric oxygen therapy" in most medical literature, however, refers to 2.0+ ATA protocols.
Are soft-shell chambers safe?
Mostly. The pressure differential is smaller than in medical chambers, so the pressure-related risks (ear barotrauma, decompression injury) are lower. Chamber fires are still possible. Patients with sinus or ear issues can still have problems.
Can I do mild HBOT at home?
Some soft-shell chamber manufacturers sell home-use units. The home use is technically permitted under FDA general wellness, but without medical oversight. Home HBOT is not a substitute for clinical care for any medical condition.
Why is medical HBOT so expensive?
Hospital-grade chambers cost $80,000 to $300,000+, the facility requires specialized fire-safety modifications, and the supervising physician must hold UHM credentials. The regulatory burden and capital investment drive the cost.
Should I try mild HBOT for my chronic condition?
Discuss with a physician who is not selling the treatment. The evidence for 1.3 ATA HBOT on most chronic conditions is weak. For FDA-approved indications, use medical HBOT at a UHMS-accredited facility instead.
Medical disclaimer: This guide is informational and does not constitute medical advice. HBOT carries real risks including ear barotrauma, oxygen toxicity, and chamber fire. Discuss any HBOT plan with a physician trained in undersea and hyperbaric medicine before starting. The FDA has cleared HBOT for 13 specific indications; uses outside those indications are off-label and not supported by FDA evaluation.
-- The HBOT Finder Team