Hyperbaric Oxygen Therapy

Hyperbaric oxygen therapy, or HBOT, means breathing 100% oxygen while sitting or lying inside a sealed chamber pressurized to well above normal atmospheric pressure. It is one of the few therapies that sits at two extremes at once: for a short list of serious medical problems it is genuinely life- and limb-saving, backed by decades of clinical evidence and covered by insurance. At the same time, it has become the centerpiece of a booming "wellness" industry that markets it for autism, aging, athletic recovery, and a long list of conditions where the evidence is thin, absent, or negative. This page is meant to help you tell those two worlds apart. We explain what the therapy actually is, the simple physics that make it work, the established uses recognized by hyperbaric medicine societies, the unproven and marketed uses, how a session feels, the real risks, who should avoid it, and the important difference between hospital-grade "hard" chambers and the inflatable "mild" chambers sold for home use. Throughout, our aim is to be plain, warm, and rigorously honest about where the science is solid and where it is not.

What HBOT Is and How a Chamber Works
The Physics: Henry's Law and Dissolved Oxygen
What a Session Actually Feels Like
Established, Evidence-Based Uses
Unproven, Off-Label, and Marketed Uses
Hard Chambers vs. Soft "Mild" Chambers
Risks and Side Effects
Who Should Avoid or Be Cautious
Telling a Real Program From a Wellness Upsell
Research Papers
Connections
Featured Videos

What HBOT Is and How a Chamber Works

In everyday life you breathe air that is about 21% oxygen at one atmosphere of pressure — the pressure at sea level, which clinicians call 1 ATA (atmospheres absolute). Hyperbaric oxygen therapy changes two things at the same time: it raises the pressure around your whole body, and it gives you nearly pure oxygen to breathe. A typical treatment presses you to somewhere between 2.0 and 3.0 ATA, which is like descending 33 to 66 feet underwater, while you breathe 100% oxygen either directly from the chamber atmosphere or through a mask or hood.

There are two main designs. A monoplace chamber is a clear acrylic tube built for one person; the entire chamber is filled with pressurized oxygen, and you simply lie back and breathe. A multiplace chamber is a room-sized steel vessel that seats several patients (and sometimes an attendant) who breathe oxygen through individual masks or hoods while the room itself is pressurized with ordinary air. Both are operated by trained staff, monitored constantly, and pressurized and depressurized slowly over several minutes so your ears and sinuses can keep up.

A course of therapy is not a single visit. For approved conditions it usually means daily sessions of roughly 90 to 120 minutes, five days a week, often for 20 to 60 sessions depending on the problem. Emergency uses, such as severe carbon monoxide poisoning or a diving injury, may be a single urgent treatment or a small number of treatments given right away.

The Physics: Henry's Law and Dissolved Oxygen

The whole therapy rests on a piece of high-school chemistry called Henry's law, which says that the amount of a gas that dissolves into a liquid is proportional to the pressure of that gas above the liquid. Your blood plasma is the liquid, and oxygen is the gas. Push more oxygen pressure onto the blood, and more oxygen physically dissolves into the watery part of it.

This matters because most of the oxygen your body carries normally rides on hemoglobin inside red blood cells, and at sea level that hemoglobin is already about 97% saturated — you cannot load it much higher just by breathing more oxygen. The plasma, by contrast, normally carries only a tiny amount of dissolved oxygen. Under hyperbaric conditions that dissolved fraction climbs dramatically: breathing 100% oxygen at 3 ATA can raise the oxygen physically dissolved in plasma more than tenfold compared with breathing air. In fact, under those conditions the plasma alone can carry enough dissolved oxygen to meet resting tissue needs, which is why hyperbaric oxygen can keep tissue alive even when red cells are blocked or poisoned.

That extra dissolved oxygen does several things. It can reach tissue that swollen, damaged, or clogged blood vessels can no longer supply well; it displaces carbon monoxide from hemoglobin far faster than breathing room air; it helps white blood cells kill certain bacteria; it stops the toxin production of some anaerobic microbes that cannot tolerate oxygen; and over a course of treatment it stimulates the growth of new small blood vessels (a process called angiogenesis) and mobilizes repair cells. Reviews of these mechanisms describe both the immediate pressure and oxygen effects and the slower, cumulative healing effects that build up over many sessions.

What a Session Actually Feels Like

Most people are surprised by how ordinary it feels. You change into cotton clothing (no synthetics, lotions, or anything that could spark, for reasons explained under risks), then settle into the chamber. As pressurization begins you feel your ears fill, exactly as they do on a descending airplane or when diving. Staff coach you to "clear" your ears by yawning, swallowing, or gently pushing air against a pinched nose. This early few minutes is the part that requires a little cooperation; once you reach treatment pressure, the fullness passes.

At pressure you can usually rest, nap, watch a screen, or listen to audio, depending on the chamber. The air may feel slightly warm during pressurization and cool during depressurization — a normal consequence of compressing and expanding gas. Sessions typically run an hour and a half to two hours. On the way back to normal pressure your ears may pop again. Afterward some people feel a little tired or lightheaded briefly, and a few notice temporary changes in near vision (see risks). For most patients the experience is calm and uneventful, and the main demand is simply the time commitment of coming back day after day.

Established, Evidence-Based Uses

Hyperbaric medicine is a real medical specialty, and the professional body that defines its legitimate scope is the Undersea and Hyperbaric Medical Society (UHMS). The UHMS maintains a list of conditions for which HBOT has enough evidence to be considered a standard or accepted treatment, and for which insurers such as Medicare will often cover it. The following are the well-supported indications. For these, HBOT is not "alternative" — it is mainstream medicine.

Decompression sickness and arterial gas embolism

These are the original reasons hyperbaric chambers exist. In decompression sickness ("the bends"), a diver who surfaces too fast forms nitrogen bubbles in blood and tissue; in arterial gas embolism, gas bubbles enter the arterial circulation and can block flow to the brain. Recompression in a chamber shrinks the bubbles by pressure and lets the excess gas redissolve and be breathed off, while high oxygen speeds the process. This is emergency treatment and remains the standard of care for serious diving injuries.

Carbon monoxide poisoning

Carbon monoxide binds hemoglobin roughly 200 times more tightly than oxygen, starving tissues and, in severe cases, causing lasting brain injury. Breathing 100% oxygen under pressure strips carbon monoxide off hemoglobin far faster than room air and floods the plasma with dissolved oxygen. A landmark randomized trial found that hyperbaric oxygen reduced the risk of long-term cognitive problems after acute poisoning, and it is used for severe cases — those with loss of consciousness, heart strain, neurological signs, or high carbon monoxide levels. It is worth knowing that not every trial agreed, and the exact patient selection is still debated, but HBOT is an accepted option for serious poisoning. Learn more on our Carbon Monoxide page.

Non-healing diabetic wounds

People with diabetes can develop foot ulcers that will not close because of poor circulation and poor oxygen delivery, and these wounds sometimes lead to amputation. HBOT is used as an add-on to good wound care for selected, serious, non-healing diabetic foot ulcers. Here the honesty matters: the evidence is genuinely mixed. One well-known randomized trial found faster healing with HBOT, while a later rigorous double-blind trial found no reduction in the need for amputation. This is a case where HBOT may help some patients but is not a guaranteed rescue, and it should be reserved for wounds that meet specific severity criteria after other measures have been optimized. See our pages on Diabetes and Type 2 Diabetes.

Radiation tissue injury

Radiation used to treat cancer can damage healthy tissue years later, leaving it poorly supplied with blood — problems such as osteoradionecrosis of the jaw, radiation injury to the bladder or bowel, and wounds that will not heal in irradiated areas. Because HBOT stimulates new blood-vessel growth in this oxygen-starved tissue, it is an established treatment for late radiation injury, and systematic reviews find reasonable evidence of benefit for several of these late complications.

Serious infections: necrotizing soft-tissue infection and gas gangrene

Some of the most dangerous infections are caused by bacteria that thrive without oxygen and destroy tissue rapidly. In gas gangrene (clostridial myonecrosis) and severe necrotizing soft-tissue infections ("flesh-eating" infections), HBOT is used alongside — never instead of — emergency surgery and antibiotics. High tissue oxygen halts toxin production by some of these organisms and supports the immune cells that fight them. See our page on Necrotizing Fasciitis.

Compromised skin grafts and flaps, and other accepted uses

When a skin graft or surgical flap is at risk of dying from poor blood supply, HBOT can help keep the tissue alive long enough for new vessels to form. The full UHMS list also includes severe anemia when transfusion is not possible, crush injury and other acute traumatic circulation problems, refractory bone infection (osteomyelitis), central retinal artery occlusion, sudden hearing loss in selected cases, and thermal burns — each with its own place in specialist practice.

Unproven, Off-Label, and Marketed Uses

Outside that established list is a large and growing market of "wellness" hyperbaric centers that advertise HBOT for conditions where the evidence is weak, preliminary, or missing entirely. In keeping with this site's mission to give ordinary people accurate information, it is important to be blunt here: most of these uses are not supported by strong clinical evidence, and some are actively marketed in ways that outrun the science.

Autism. HBOT has been aggressively promoted for autistic children. One small randomized trial reported modest improvements, but it has been widely criticized, and subsequent studies did not confirm a real benefit. Major pediatric and autism organizations do not endorse HBOT as a treatment for autism, and it should be viewed as unproven.
Anti-aging and "longevity." Clinics market HBOT to reverse aging, lengthen telomeres, and boost brain performance in healthy people. This is based largely on small, short, industry-adjacent studies without long-term or hard clinical outcomes. The underlying "hyperoxic-hypoxic paradox" is a real and interesting area of research, but it is far from proving that repeated HBOT makes healthy people live longer or better. Treat longevity claims with skepticism. See our Longevity Protocols page.
General "wellness," athletic recovery, energy, and detox. Marketing promises faster recovery, more energy, and "detoxification." There is little rigorous evidence that HBOT does any of this for healthy or lightly injured people, and the claims often borrow the credibility of the genuine, serious indications above.
Long-lingering post-viral fatigue. Some clinics advertise HBOT for persistent post-viral symptoms. The evidence is preliminary and far from conclusive, and it should be considered unproven rather than an established treatment.
Fibromyalgia, stroke recovery, traumatic brain injury, and others. These are active research areas with some encouraging early studies but no settled answer. A single positive small trial is not proof; be cautious about paying out of pocket for a therapy still being tested.

None of this means HBOT is fake. It means the label matters enormously: the same machine that saves a diver or a poisoned patient is often being sold for problems it has never been shown to fix. If a clinic advertises HBOT as a cure-all, that is a warning sign, not a selling point.

Hard Chambers vs. Soft "Mild" Chambers

One of the biggest sources of confusion — and marketing mischief — is the difference between medical "hard" chambers and the inflatable "soft" chambers sold for clinics and homes.

Hard chambers are rigid steel or thick acrylic vessels that can safely reach the 2 to 3 ATA pressures used in real hyperbaric medicine, and they deliver 100% oxygen. These are what hospitals and accredited hyperbaric centers use for the approved indications.

Soft chambers, often marketed as "mild hyperbaric" or mHBOT, are fabric, zip-up bags inflated with ordinary air (sometimes with an oxygen concentrator added) to only a small pressure above sea level — typically around 1.3 ATA. That is far below the pressure of genuine HBOT, and the added dissolved oxygen is a fraction of what a medical chamber delivers. There is little evidence that mild soft-chamber sessions produce the clinical effects claimed for real HBOT, and the term "hyperbaric" on the label can create a false impression of medical equivalence. The regulatory picture reflects this: low-pressure soft chambers are cleared for only a narrow set of purposes, and using them to "treat" the serious conditions above is not appropriate. If you are considering a home or clinic soft chamber, understand that you are not getting the therapy studied in the trials described on this page.

Risks and Side Effects

HBOT is generally safe when delivered by trained staff for appropriate reasons, but it is a real medical treatment with real risks, not a spa service. The most common and the most serious problems both come from the two forces involved: pressure and oxygen.

Ear and sinus barotrauma. This is by far the most common side effect. As pressure rises, the eardrum and sinuses can hurt or be injured if you cannot equalize the pressure, just as with flying or diving. Slow pressurization and ear-clearing techniques prevent most cases; occasionally a person needs ear tubes to tolerate treatment.
Temporary nearsightedness (myopia). Repeated sessions can reversibly change the lens of the eye, making near vision blurrier over a course of treatment. It usually returns to baseline over weeks to months after therapy ends. Cataracts can worsen with very prolonged courses.
Oxygen toxicity seizures. Breathing oxygen at high pressure can, uncommonly, overexcite the brain and trigger a seizure during a session. These are usually brief and resolve when the oxygen is reduced, and protocols include "air breaks" to lower the risk. Oxygen can also irritate the lungs with very long or repeated exposure.
Fire risk. An oxygen-rich, pressurized environment makes fire vastly more dangerous. This is why patients must remove synthetic clothing, cosmetics, hair products, lotions, electronics, and anything that could spark. Rare but catastrophic chamber fires have occurred, almost always in unregulated settings that ignored these rules — another reason to use accredited facilities.
Confinement and pressure discomfort. Some people feel claustrophobic in a monoplace tube. Rarely, pressure changes can affect the lungs, and pre-existing lung problems raise that risk (see below).

Who Should Avoid or Be Cautious

A few situations make HBOT dangerous or require special care, which is why every legitimate program screens patients first.

Untreated pneumothorax. A collapsed lung with trapped air is the classic absolute contraindication — changing pressure can expand the trapped gas dangerously. It must be treated before any hyperbaric exposure.
Certain lung conditions. Severe emphysema, large air-filled lung cysts (bullae), or a recent history of spontaneous lung collapse raise the risk of pressure-related lung injury and need specialist evaluation.
Ear, sinus, or airway problems. Active congestion, recent ear surgery, or an inability to equalize ear pressure make barotrauma more likely and may need to be addressed first.
Certain medications and chemotherapy agents. A few drugs interact badly with hyperbaric oxygen; your hyperbaric physician reviews your medication list before treatment.
Uncontrolled fever or seizure disorders, claustrophobia, uncontrolled high blood sugar, and pregnancy are situations that call for individual judgment rather than a blanket rule.

The practical takeaway: HBOT should be prescribed and supervised by clinicians who have examined you, not sold from a menu. Proper screening is part of what separates a medical program from a wellness storefront.

Telling a Real Program From a Wellness Upsell

If someone recommends HBOT to you, a few plain questions cut through most of the confusion:

Is my condition on the established list? Decompression sickness, gas embolism, serious carbon monoxide poisoning, selected non-healing diabetic wounds, radiation tissue injury, certain severe infections, and compromised grafts are supported. Autism, aging, general wellness, and most everything else are not.
Is this a hard chamber at medical pressures (2–3 ATA) with 100% oxygen, or a soft "mild" bag at about 1.3 ATA? For a serious indication, only a hard chamber is appropriate.
Is the facility accredited and physician-supervised, with staff trained to screen me and manage emergencies?
Will insurance cover it? Coverage for an approved indication is a useful reality check; if a clinic asks for large cash payments for an unproven use, be skeptical.
What does the clinic claim it treats? A short, specific list is reassuring. A long menu of unrelated conditions — from autism to anti-aging to "detox" — is a red flag.

Used for the right reasons, hyperbaric oxygen therapy is a powerful and sometimes life-saving tool. Used as a cure-all, it is an expensive way to breathe. Knowing the difference is the whole point of this page.

Research Papers

Tibbles PM, Edelsberg JS. Hyperbaric-oxygen therapy. New England Journal of Medicine. 1996;334(25):1642-1648. doi:10.1056/NEJM199606203342506 — a classic clinical overview of how HBOT works and its accepted indications.
Leach RM, Rees PJ, Wilmshurst P. ABC of oxygen: Hyperbaric oxygen therapy. BMJ. 1998;317(7166):1140-1143. doi:10.1136/bmj.317.7166.1140 — a plain-language introduction to the physics and clinical use of the therapy.
Thom SR. Hyperbaric oxygen: its mechanisms and efficacy. Plastic and Reconstructive Surgery. 2011;127(Suppl 1):131S-141S. doi:10.1097/PRS.0b013e3181fbe2bf — reviews the biological mechanisms, including angiogenesis and immune effects.
Weaver LK, Hopkins RO, Chan KJ, et al. Hyperbaric oxygen for acute carbon monoxide poisoning. New England Journal of Medicine. 2002;347(14):1057-1067. doi:10.1056/NEJMoa013121 — the pivotal randomized trial showing reduced cognitive problems after severe poisoning.
Weaver LK. Carbon monoxide poisoning. New England Journal of Medicine. 2009;360(12):1217-1225. doi:10.1056/NEJMcp0808891 — a clinical-practice review of when hyperbaric oxygen is indicated for carbon monoxide poisoning.
Vann RD, Butler FK, Mitchell SJ, Moon RE. Decompression illness. The Lancet. 2011;377(9760):153-164. doi:10.1016/S0140-6736(10)61085-9 — comprehensive review of decompression sickness and gas embolism, the original hyperbaric emergencies.
Löndahl M, Katzman P, Nilsson A, Hammarlund C. Hyperbaric oxygen therapy facilitates healing of chronic foot ulcers in patients with diabetes. Diabetes Care. 2010;33(5):998-1003. doi:10.2337/dc09-1754 — a randomized trial reporting improved healing of diabetic foot ulcers.
Fedorko L, Bowen JM, Jones W, et al. Hyperbaric oxygen therapy does not reduce indications for amputation in patients with diabetes with nonhealing ulcers of the lower limb. Diabetes Care. 2016;39(3):392-399. doi:10.2337/dc15-2001 — a rigorous double-blind trial that found no benefit, showing why the diabetic-wound evidence is mixed.
Kranke P, Bennett MH, Martyn-St James M, Schnabel A, Debus SE, Weibel S. Hyperbaric oxygen therapy for chronic wounds. Cochrane Database of Systematic Reviews. 2015;(6):CD004123. doi:10.1002/14651858.CD004123.pub4 — systematic review finding short-term but uncertain long-term wound-healing benefit.
Bennett MH, Feldmeier J, Hampson NB, Smee R, Milross C. Hyperbaric oxygen therapy for late radiation tissue injury. Cochrane Database of Systematic Reviews. 2016;(4):CD005005. doi:10.1002/14651858.CD005005.pub4 — systematic review supporting HBOT for several late radiation complications.
Heyboer M, Sharma D, Santiago W, McCulloch N. Hyperbaric oxygen therapy: side effects defined and quantified. Advances in Wound Care. 2017;6(6):210-224. doi:10.1089/wound.2016.0718 — a practical catalog of how common each side effect really is.
Rossignol DA, Rossignol LW, Smith S, et al. Hyperbaric treatment for children with autism: a multicenter, randomized, double-blind, controlled trial. BMC Pediatrics. 2009;9:21. doi:10.1186/1471-2431-9-21 — the small, much-debated trial often cited to market HBOT for autism; later work did not confirm benefit.

Back to Table of Contents

Connections