Why scientists are exploring brain cooling as a defence against altitude sickness

Kirill Skorobogatko/Shutterstock In the 2021 Netflix documentary 14 Peaks: Nothing Is Impossible, elite mountaineer Nirmal Purja races up the world’s highest summits at extraordinary speed. But even he isn’t immune to altitude. During one ascent, Purja develops symptoms of high-altitude cerebral oedema (brain swelling), a dangerous form of altitude sickness that can strike with little warning. It’s a stark reminder that when oxygen levels fall, no amount of fitness or experience guarantees protection. Research from my colleagues and I suggests that much of the damage caused by altitude sickness begins with stress inside the brain itself. If we can reduce that stress early, we may be able to interrupt the chain reaction that leads to more serious symptoms. Each year, thousands of trekkers and climbers develop some form of altitude illness after ascending above about 2,500 metres. The mild form, acute mountain sickness, is common and unpleasant: headaches, nausea, dizziness and fatigue. More severe conditions, including high-altitude cerebral oedema and high-altitude pulmonary oedema, (swelling in the lungs) can be fatal if not treated quickly. Different medications can help but are far from perfect. A diuretic medicine known as acetazolamide encourages breathing to improve oxygen levels. A steroid drug called dexamethasone can be lifesaving in high-altitude cerebral oedema, while nifedipine (a blood pressure drug) or sildenafil (better known as Viagra) can ease high altitude pulmonary oedema by reducing pressure in the lungs. But these medications come with side-effects, some of which mimic altitude sickness itself. And the only guaranteed treatment – descending to a lower altitude – is not always possible in bad weather or on crowded mountain routes. Supplemental oxygen works well once illness develops, but it is heavy, expensive and can interfere with natural acclimatisation. It’s an effective rescue tool, not a practical preventive one for most mountaineers. So what if we could be proactive rather than reactive? Why cooling the brain might help Targeted brain cooling (or therapeutic hypothermia) has long been used in hospitals for cardiac arrest, newborn babies who need oxygen, as well as treating traumatic brain injury. The principle is simple – a cooler brain requires less oxygen and generates fewer metabolic byproducts. The byproducts being referred to here are called “free radicals”. These highly reactive molecules increase when the body is stressed, as it is at altitude where oxygen is scarce. In excess, they cause what scientists call “oxidative stress”, damaging brain cells, weakening the blood–brain barrier and triggering inflammation. They also interfere with nitric oxide, a chemical that helps blood vessels open properly. Together, these effects disrupt blood flow and allow fluid to leak into brain tissue, which are processes thought to underpin acute mountain sickness and high-altitude cerebral oedema. Think of it like this: at high altitude, free radicals act like rust in your brain’s plumbing. They eat away at the seals and allow fluid to seep where it shouldn’t. Research suggests that lowering brain temperature by just 1°C can reduce its metabolic rate – and therefore oxygen demand – by roughly 5% to 9%. With less demand comes fewer free radicals and potentially less swelling. Individually, these changes are modest. Combined, they could offer meaningful protection.

How do you cool a brain on a mountain? Whole-body hypothermia is dangerous and impractical outdoors. So, the goal is selective brain cooling. In other words, lowering brain temperature while keeping the rest of the body warm. Several types of technology make this possible. Cooling helmets, already used in neurocritical care, can reduce brain temperature by nearly 2°C within an hour while leaving core temperature stable. Cervical cooling collars are devices designed to be worn around the neck and upper shoulder area, and can target the major blood vessels supplying the brain. They have shown promising improvements in cerebral blood flow. Intranasal cooling systems exist too, but they are too invasive for healthy mountaineers. So, helmets and collars are the most realistic options for expedition use. They are portable, non-invasive and are becoming lighter. But they are still far from being standard trekking gear. There is another complication. At altitude, the brain naturally increases blood flow in an effort to deliver more oxygen. That warm blood acts like a radiator, potentially cancelling out cooling if devices are used too late. Early application, before this response kicks in, may be crucial. Right now, we simply don’t know whether this could help prevent altitude sickness. The theory is strong, however, and evidence from other neurological conditions is encouraging. But selective brain cooling has not yet been tested in real (or simulated) high-altitude environments. We don’t know whether field-based cooling could meaningfully reduce oxidative stress, or whether mountaineers could even tolerate wearing cooling gear during long ascents. Altitude sickness is typically mild but can sometimes turn very serious − a high-altitude medicine physician explains how to safely prepare

Still, given the shortcomings of current treatments, and the growing popularity of high-altitude travel, the idea deserves serious investigation. Laboratory studies using simulated hypoxia (when there is less oxygen in the air), wearable biosensors and eventually field trials on trekking routes could help determine whether “brain chill” offers genuine protection. For now, selective brain cooling remains an intriguing, speculative strategy. At best, it would complement rather than replace the basics of altitude safety – gradual ascent, early symptom recognition and timely descent. Purja’s near miss in 14 Peaks shows that the mountains do not discriminate. If a simple, non-drug intervention could buy climbers more time or reduce risk, it could become a valuable addition to the mountaineer’s toolkit. Whether cooling your head could help you keep your cool at altitude remains an open question. But it’s one worth exploring.

Adnan Haq does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.