Why Do So Many People Think Hyperbaric Oxygen Therapy Is Always 2.4 ATA?

If you've been researching hyperbaric oxygen therapy (HBOT) online, you've probably noticed one number appearing over and over again:

2.4 atmospheres absolute (ATA).

Many websites describe this as the "standard" treatment pressure for HBOT, leading people to assume that every hyperbaric treatment should be delivered at 2.4 ATA.

But that's only part of the story.

In reality, 2.4 ATA is primarily associated with the traditional hospital-based indications recognised by organisations such as the Undersea and Hyperbaric Medical Society (UHMS). These include conditions such as decompression illness, carbon monoxide poisoning, radiation tissue injury, diabetic foot ulcers, chronic refractory osteomyelitis, compromised grafts and flaps, and other serious conditions where HBOT has become an established part of medical care.

Many of these are what I often describe as "save a life" or "save a limb" indications—conditions where restoring oxygen delivery can prevent major disability or even death.

However, outside the hospital environment, a very different evolution has been taking place.

Across Europe, Israel, Australia, New Zealand and North America, many private hyperbaric clinics and research groups are increasingly using lower treatment pressures—typically between 1.6 and 2.0 ATA—for conditions that fall outside the traditional approved indications.

These include:

• Neurological rehabilitation

• Mild traumatic brain injury

• Persistent post-concussion symptoms

• Stroke recovery

• Long COVID

• Chronic fatigue syndromes

• Musculoskeletal injuries

• Sports recovery and athletic performance

• Difficult-to-heal wounds

• Healthy ageing and longevity research

This naturally raises an important question.

If 2.4 ATA is considered the "standard," why are so many experienced clinicians and researchers now using lower pressures?

The answer is surprisingly historical.

How did 2.4 ATA become the standard?

Much of modern HBOT practice evolved from early clinical experience, U.S. Navy treatment tables, and the wound-healing protocols developed during the 1960s and 1970s.

Clinicians discovered that pressures around 2.0–2.5 ATA produced excellent tissue oxygenation while avoiding much of the increased oxygen toxicity associated with higher pressures such as 2.8 or 3.0 ATA.

Over time, 2.4 ATA became the go-to dosage for repeated daily treatments of the previously mentioned serious conditions.

These protocols were eventually incorporated into training programmes, clinical guidelines, reimbursement systems and hospital practice.

This created what might be described as a self-reinforcing cycle.

Because 2.4 ATA became the accepted standard, most subsequent clinical trials also used 2.4 ATA. Those studies then reinforced the perception that 2.4 ATA was the "correct" dose.

Yet one important fact is often overlooked.

Very few studies have directly compared different HBOT pressures.

In other words, while we know HBOT works for many conditions, we still know remarkably little about the optimal pressure, treatment duration, treatment frequency or total number of sessions for most diseases.

Three pioneers who changed the conversation

Over the past three decades, three influential researchers have fundamentally changed the way many clinicians think about HBOT dosing.

Professor Philip James: Oxygen is the medicine

Professor Philip James has consistently reminded the hyperbaric community that oxygen—not pressure—is the therapeutic agent.

Pressure is simply the vehicle that delivers oxygen into tissues.

His philosophy has always been to use the lowest effective dose capable of achieving the desired biological response, recognising that increasing pressure also increases oxidative stress and oxygen toxicity.

Dr Paul Harch: Every disease has its own dose

Dr Paul Harch proposed that HBOT should be prescribed much like any other medication.

Rather than asking, "What is the standard pressure?", he asked:

"What is the correct dose for this disease?"

His work in neurological disorders challenged the long-held belief that "more pressure is always better," demonstrating that lower pressures may actually produce superior outcomes for some patients.

Professor Shai Efrati: Enter the molecular era

Professor Shai Efrati has provided the molecular explanation.

His research has shown that intermittent hyperoxia activates numerous regenerative pathways involved in neuroplasticity, stem cell mobilisation, angiogenesis, mitochondrial function and gene expression.

His work describing the Hyperoxic-Hypoxic Paradox suggests that carefully controlled oxygen fluctuations may stimulate many of the regenerative mechanisms that clinicians are trying to achieve—without necessarily requiring higher treatment pressures.

The future may be precision oxygen therapy

Today, growing numbers of clinicians are successfully using treatment pressures such as:

• 1.6 ATA

• 1.8 ATA

• 2.0 ATA

for selected neurological, musculoskeletal and regenerative applications.

This does not mean that 2.4 ATA is obsolete.

Higher pressures remain essential for many established medical indications and continue to save lives and limbs every day.

However, the emerging evidence suggests that the optimal dose depends on the biological target rather than a single "standard" pressure.

Perhaps the future of HBOT is not asking:

"What pressure should we treat at?"

Instead, we should be asking:

"What biological response are we trying to achieve?"

As our understanding of oxygen biology continues to evolve, hyperbaric medicine is moving away from a one-size-fits-all approach and towards precision oxygen therapy—selecting the right pressure, treatment duration and treatment frequency for the individual patient and the condition being treated.

The next question is whether a new generation of research will show that for many injuries, conditions, and for optimal physical performance, less pressure may actually be more.

- Samantha Winters