By Louisa Lee, FMCHC · Updated August 2026
The honest answer is: possibly, for some people, at a dose most wellness sessions do not deliver. A randomised sham-controlled trial found that 40 sessions of hyperbaric oxygen improved global cognitive function in people with post-COVID symptoms (Zilberman-Itskovich et al., 2022). Across the wider literature the results are mixed, and no agreed protocol exists. A single session is not what was studied.
Brain fog is a description, not a diagnosis. People use it for losing the thread mid-sentence, rereading the same paragraph three times, or finding that work which took an hour now takes three. Because it is a description rather than a condition, it has no single cause and no single answer. The commonest drivers in working adults are unremarkable: accumulated sleep debt, sustained stress load, low iron or thyroid function, alcohol, certain medications, the hormonal shifts of perimenopause, and recovery from a viral illness. That matters for anyone considering a therapy for it, because the useful question is never “what fixes brain fog” but “what is producing mine”.
Common enough that the government measures it. Answering a parliamentary question on 22 September 2025, the Ministry of Manpower reported that among more than 15,000 employees whose employers used the iWorkHealth assessment tool in 2024, about one in three had experienced work-related stress or burnout (Ministry of Manpower, 2025). MOM adds its own caveat, which is worth carrying: participation in iWorkHealth is voluntary, so the sample may not represent the whole workforce. Read it as a signal of scale rather than a precise national rate. Stress and burnout are not brain fog, but they are among its most reliable producers, which is why so many people in Singapore arrive at this question through work rather than illness.
The proposed mechanism is that pressure changes how much oxygen your blood can carry, and the brain is the organ least tolerant of a shortfall. Under normal conditions almost all the oxygen in your blood travels bound to haemoglobin, which is close to saturated already, so breathing harder adds very little. Raising the ambient pressure while you breathe oxygen-enriched air pushes additional oxygen into the plasma itself, where it dissolves and can reach tissue independently of red blood cells. The research interest in cognition rests on the idea that this may support tissue where blood flow is impaired, and the 2022 post-COVID trial did report changes in brain perfusion on MRI alongside its cognitive findings (Zilberman-Itskovich et al., 2022). That is a plausible mechanism with imaging alongside it, which is not the same as a demonstrated benefit for everyday tiredness. Our overview of hyperbaric oxygen therapy in Singapore covers the basics of how a session works.
Mixed results overall, with one strong recent trial and a large body of older work that does not agree with itself. The most rigorous evidence is a randomised, sham-controlled, double-blind trial of 73 people with post-COVID symptoms lasting at least three months. Those receiving hyperbaric oxygen showed significant improvement against sham in global cognitive function (effect size 0.495, p = 0.038), attention (0.477, p = 0.04) and executive function (0.463, p = 0.05), along with energy, sleep and pain measures (Zilberman-Itskovich et al., 2022). Those are modest-to-moderate effects in a small sample, and several of the authors declare financial interests in a hyperbaric company, which is disclosed in the paper and worth knowing when you read it.
Set against that, a systematic review published in Neuropsychology Review gathered 42 studies of hyperbaric oxygen and cognition across a range of neurological conditions and reported that the findings were inconsistent. Its authors were direct about why, noting that “there is still no agreement about an HBOT protocol, specifically the appropriate air pressure and the time and repetition of treatment sessions”, and concluded only that hyperbaric oxygen “may have potential” once the methodological problems they describe are addressed (Marcinkowska et al., 2021). A field with no agreed protocol is a field where two studies can reach opposite conclusions while both being competently run.
Pressure appears to matter a great deal, and this is the detail most pages leave out. The post-COVID trial that produced the clearest cognitive result used 2.0 ATA for 90 minutes, with five-minute air breaks every 20 minutes, 40 sessions over two months (Zilberman-Itskovich et al., 2022). Soft-shell wellness chambers, including the one used at Avantir, operate at 1.5 ATA. That is a real difference in the intervention, not a marketing distinction.
Lower pressure is not automatically weaker. A dosage-focused systematic review found that 40 sessions at 1.5 ATA produced statistically significant cognitive improvements across four randomised trials in people with persistent post-concussion syndrome after mild traumatic brain injury, and argued that pressure within a narrow range may matter more than the oxygen concentration (Harch, 2022). Its author also co-owns a hyperbaric business, which is disclosed. Pulling the other way, a review of hyperbaric oxygen in children with cerebral palsy, where trials used 1.5 to 1.75 ATA, concluded there was high-level evidence of no benefit to motor or cognitive function, and found middle ear barotrauma in up to half of the children (Laureau et al., 2022). Low pressure works in some populations and not in others, and neither result transfers automatically to a healthy adult who is simply tired.
| The post-COVID cognition trial | A typical wellness session | |
|---|---|---|
| Pressure | 2.0 ATA | 1.5 ATA soft-shell |
| Sessions | 40, five days a week for two months | Booked one at a time |
| Population | Symptoms for 3+ months after confirmed infection | Generally well adults |
Around 40, consistently, across the protocols that reported a cognitive benefit. The post-COVID trial used 40 daily sessions over two months. The post-concussion trials in the dosage review used 40 sessions at 1.5 ATA. That consistency is the single most practical thing in this literature, and it is the thing least often mentioned in consumer material. No published trial has shown that one session, or three, does what 40 did. If you are weighing this up, the realistic question is not whether to try a session but whether a course of that size fits your time and your budget, and whether the reason for your brain fog is the kind these trials were studying. Two sessions is not a fair test of it, and neither is forty booked on the strength of a page like this one.
Side effects in the main cognitive trial were common in both arms and no more frequent with real treatment than with sham: 35.1% of the hyperbaric group and 38.9% of the sham group reported one, and no participant stopped because of them (Zilberman-Itskovich et al., 2022). The most frequent issue with pressure is ear and sinus barotrauma, which is why the paediatric review recorded rates as high as 50% in young children (Laureau et al., 2022). Hyperbaric sessions are generally not suitable if you have untreated pneumothorax, certain ear or lung conditions, uncontrolled fever, or if you are pregnant, and any current medication or implanted device should be raised beforehand. Speak to your doctor before booking if any of that applies. Our page on HBOT for recovery and energy covers what a session involves in more detail.
The unglamorous causes, because they are far more likely and most of them are correctable. Before spending on any therapy for brain fog, establish how much sleep you are getting and how broken it is, since chronic short sleep produces exactly this symptom cluster and no amount of oxygen substitutes for it. A blood panel covering thyroid function, iron and ferritin, vitamin B12 and vitamin D catches several common and treatable causes. Women in their forties and fifties should consider whether this sits alongside other changes, because cognitive complaints are a recognised part of the perimenopausal picture and are often attributed to stress instead. Alcohol, antihistamines and some blood pressure medications all contribute. A root-cause approach to persistent fatigue starts here rather than with a device, and sleep quality is usually the first thing worth working on.
It may, for some people, at doses most wellness bookings do not reach. One randomised sham-controlled trial of 73 people with post-COVID symptoms found significant improvement in global cognition, attention and executive function after 40 sessions. A broader review of 42 studies found results inconsistent and no agreed protocol. It is a reasonable thing to explore and not an established answer.
The protocols that reported a cognitive benefit used around 40 sessions, delivered five days a week over roughly two months. No published trial has shown that a single session or a short handful produces the same result. If you are considering it, plan around the size of the course rather than around one appointment, and treat a two-session trial as inconclusive rather than as evidence of failure.
Not always. The clearest post-COVID cognition trial used 2.0 ATA. Separately, four randomised trials in persistent post-concussion syndrome did report significant cognitive improvement at 1.5 ATA across 40 sessions. So 1.5 ATA has supporting evidence in that specific population, while the strongest post-COVID result came from a higher pressure. The pressure is part of the intervention and worth asking about.
In the main cognitive trial, side effects were reported by 35.1% of the hyperbaric group and 38.9% of the sham group, and nobody discontinued because of them. Ear and sinus barotrauma is the most common issue with pressure. Sessions are generally unsuitable during pregnancy, with untreated pneumothorax, and with some ear and lung conditions. Raise any medication or implanted device with your doctor first.
Very often, yes. Sleep debt, low iron or ferritin, thyroid changes, vitamin B12 or D deficiency, alcohol, some medications, and perimenopause all produce the same symptom cluster and most are correctable. A blood panel and an honest look at your sleep will resolve more cases than any device. Working through those first also tells you whether something is left over that a therapy might address.
No. Persistent cognitive change deserves a medical assessment first, both because the common causes are treatable and because a few uncommon ones matter. Wellness sessions are not a substitute for that assessment. If your thinking has changed noticeably, or has worsened over weeks, see your doctor before spending on any therapy programme.
The interesting thing about hyperbaric oxygen and cognition is not that the evidence is bad, it is that the evidence is specific: a particular dose, over a particular course, in particular groups of people. Very little consumer writing carries that specificity across, which is how a therapy studied at 40 sessions ends up sold as a single afternoon. If you are curious, go in knowing what was actually tested. Book a consultation at Avantir Wellness in Katong to talk through whether it fits what you are dealing with.
Louisa Lee is the Founder of Avantir Wellness and a Functional Medicine Certified Health Coach (FMCHC). She champions the philosophy “Breathe Right, Sleep Well, Live Long”, helping people optimise their healthspan through sleep, airway health, lifestyle change, and evidence-informed wellness technologies. Read more on her author profile.
