History of hyperbaric oxygen.

Nathaniel Henshaw, a British physician, builds the first known pressurised therapeutic chamber in Ireland. He calls it a domicilium — a small sealed room pressurised by bellows. Henshaw believes elevated pressure aids digestion and treats acute conditions; depressurised exposure treats chronic illness.

He publishes his ideas in Aero-Chalinos (1664). The mechanism is wrong (oxygen wouldn't be discovered for another 110 years), but the empirical observation — that pressure changes biology — is correct, and the idea sticks.

The domicilium is largely forgotten for the next 170 years.

Antibiotic discovery and the pharmaceutical revolution displace hyperbaric medicine in mainstream care. The technique survives mainly in two contexts: respiratory medicine (limited use), and the dive industry.

Naval and commercial diving generates the decompression-sickness problem — the bends — and with it the first rigorous research on pressure physiology. Haldane (1908) develops the staged-decompression tables that make deep diving survivable. The relationship between hyperbaric exposure and tissue oxygen / nitrogen dynamics becomes scientific rather than empirical.

By mid-century, hyperbaric chambers exist mainly in military and commercial diving operations. Therapeutic use is largely dormant. The post-war pharmaceutical era doesn't leave much room for pressurised oxygen medicine.

Boerema's work catalyses hyperbaric medicine's second renaissance. Hospital hyperbaric units open across Europe and North America through the 1960s. Carbon monoxide poisoning, decompression sickness, gas gangrene, and crush injuries become established indications.

In 1967, the Undersea Medical Society is founded in the United States — the body that will eventually become the Undersea and Hyperbaric Medical Society (UHMS), the standard-setting organisation for hyperbaric medicine globally. It defines training standards, certifies chambers, and maintains the list of approved indications that still anchors clinical HBOT today.

Jacques Cousteau's work expanding recreational diving in the 1960s also drives popular awareness of hyperbaric exposure. The Cousteau Society funds research on diving physiology that further refines decompression and hyperbaric oxygen treatment.

In the early 2000s, soft-shell chambers (Vitaeris, OxyHealth, Summit-to-Sea) open the door to wellness-side HBOT. Operating at 1.3 ATA — below the medical-indication pressures but still meaningfully above sea level — they make hyperbaric exposure accessible outside hospitals.

The category attracts mixed reception. Proponents point to plausible mechanisms (improved cerebral perfusion, mild stem cell mobilisation, sleep support). Critics correctly note that the headline RCT evidence is at 2.0 ATA, not 1.3 ATA. The space accumulates both genuine value and overstated marketing through the 2000s.

Athletes are early adopters. Michael Phelps's use in the 2000s training cycles, NBA franchise adoption (LeBron James, Cristiano Ronaldo's Real Madrid era), and the broader celebrity recovery-tool trend make HBOT mainstream-aware for the first time.

Zilberman-Itskovich et al. (2022, Scientific Reports) publish the long-COVID RCT — 73 patients, sham-controlled, 40 sessions at 2.0 ATA — with significant improvements in cognitive function, energy, sleep, psychiatric symptoms and pain. The sham used a small pressure increase with normal air, the strongest blinding HBOT research has produced.

Long COVID's emergence as a global condition coincides with the strongest sham-controlled HBOT trial to date. The result puts HBOT in the conversation for the millions of people living with post-viral fatigue and brain fog — and expands wellness-side HBOT demand sharply.

Today, HBOT sits at the most interesting moment in its history. Three centuries after Henshaw, the field has rigorous RCT evidence for the strongest aging signal published, FDA-cleared medical indications, an active wellness category, and an explosion of new research into cognitive, neurological, and longevity applications. R1SE Kelham opened in 2024 to bring trial-grade HBOT (2.0 ATA hard-shell) to Sheffield — one of the few UK wellness facilities running hard-shell at the dose that underwrites the cited research.