6 Things That Happen Inside Your Body During a Hyperbaric Session

From the outside, a hyperbaric oxygen therapy (HBOT) session looks almost boringly calm: someone lying comfortably in a chamber, reading or dozing while the pressure rises. But under the surface, your physiology is doing some genuinely fascinating things. Here are six of the stranger ones – and why they matter.

1. Your blood starts carrying oxygen in an unusual way

Normally, almost all the oxygen in your blood hitches a ride on haemoglobin inside your red blood cells. But here’s the quirk: those cells are already nearly full at sea level, so simply breathing harder can’t add much more. Inside a hyperbaric chamber, the increased pressure forces large amounts of oxygen to dissolve directly into the blood plasma – the liquid part – bypassing the red cells entirely. This is oxygen delivery through a side door your body rarely uses, and it lets oxygen reach places normal circulation struggles to supply. Our explainer on how hyperbaric chambers work breaks the physics down further.

2. Your ears do the “aeroplane” thing

This one you’ll actually feel. As pressure increases, the air in your middle ear compresses, creating that familiar full or blocked sensation you get during a flight’s descent. Your body handles it the same way – a swallow, a yawn, or a gentle equalisation technique pops things back to normal. It’s completely routine, but it’s the most noticeable sign that real pressure changes are happening around you. Our guide to what to expect and possible side effects covers how to manage it smoothly.

3. Oxygen-starved tissues get a rare drink

Some tissues in the body are chronically under-supplied with oxygen – around old injuries, inflamed areas, or regions with poor circulation. Because plasma is a fluid, the dissolved oxygen can seep into these hard-to-reach zones far more effectively than red-cell-bound oxygen can. It’s a bit like watering the corners of a garden the sprinkler never quite reaches. This is central to why HBOT is studied for healing and recovery.

4. Your body may start building new blood vessels

Give it repeated sessions, and something remarkable is thought to happen over time: the oxygen-rich environment can stimulate angiogenesis, the growth of new small blood vessels. More vessels mean better long-term blood supply to the treated tissue – a structural change rather than a temporary boost. This regenerative effect is one of the most studied and interesting aspects of HBOT, summarised in this review in Frontiers in Neurology.

5. Your inflammation and repair signals shift

At the cellular level, the pressure-and-oxygen combination is thought to influence the signals that govern inflammation, stem cell activity, and tissue repair. Rather than simply “adding oxygen,” HBOT appears to nudge the body’s own regenerative machinery – which is why the effects tend to build gradually and can outlast the session itself. It’s less like a caffeine hit and more like tending a slow-burning fire.

6. You often feel calm – sometimes sleepy

Here’s the pleasant surprise. Many people find sessions deeply relaxing, and a fair number drift off. Part of it is the enforced stillness; part may be the physiological shift as tissues are richly oxygenated. Whatever the mechanism, “I slept better that night” is one of the most common things new users report – which is why HBOT and sleep are so often discussed together, as we explore in our piece on oxygen and better sleep.

The takeaway

A hyperbaric session may look uneventful, but your body is quietly doing several clever things at once – rerouting oxygen delivery, reaching neglected tissues, and nudging its own repair systems into gear. None of it is instant or magical, and HBOT isn’t a cure-all; the changes are subtle and cumulative. But understanding what’s happening under the calm surface makes it a lot easier to appreciate why so many people build regular sessions into their routine – ideally with a healthcare professional’s guidance.

Frequently Asked Questions

What actually happens to oxygen in my blood during HBOT?

Under increased pressure, large amounts of oxygen dissolve directly into your blood plasma rather than only binding to red blood cells. This lets oxygen reach tissues that normal circulation struggles to supply.

Why do my ears feel blocked in the chamber?

The pressure change compresses air in your middle ear, just like during an aeroplane’s descent. Swallowing, yawning, or gentle equalisation techniques relieve it. It’s normal and usually easy to manage.

Can HBOT really grow new blood vessels?

Research suggests that repeated sessions can stimulate angiogenesis – the growth of new small blood vessels – over time. This is a gradual, structural effect rather than a temporary one, and it’s a key reason HBOT is studied for recovery.

Why do I feel sleepy or calm during a session?

Many users find sessions relaxing, partly due to the enforced stillness and partly due to the physiological effects of rich tissue oxygenation. Better sleep afterwards is a commonly reported experience.

Are these effects immediate?

Mostly no. Some sensations (like ear pressure) are immediate, but the meaningful effects – improved circulation, repair, and vessel growth – build cumulatively over a course of sessions rather than after one visit.

This article is for informational purposes only. Hyperbaric oxygen products are intended for wellness use and are not intended to diagnose, treat, cure, or prevent any disease. Always consult a qualified healthcare professional before beginning any new therapy.