Above roughly 2,500 metres, the air holds noticeably less oxygen, and your body needs time to adjust — that adjustment is acclimatization. Rush it, and altitude sickness follows: headache, nausea, dizziness, and exhaustion that can strike anyone, however fit, and however many times they have been fine before. The good news, confirmed by mountain medicine and generations of trekker experience, is that altitude sickness is largely preventable with a few simple, disciplined habits.
How Acclimatization Works
When you ascend, your body compensates by breathing faster and deeper, producing more red blood cells, and adjusting blood chemistry. This takes days, not hours — which is why the single biggest risk factor for altitude sickness is speed of ascent, not fitness. Previous trouble-free trips give you no guarantee for the next one; susceptibility varies from person to person and even from trip to trip. The practical consequence: plan your itinerary around your body’s clock, not your ambition. An extra rest day at intermediate altitude is the cheapest insurance on any high trek.
Safe Ascent Rates
The widely cited guideline from mountain-medicine practice is to limit your sleeping-altitude gain to about 300–500 metres per day once you are above 3,000 metres, and to add an extra acclimatization day every three to four days of gain. The classic technique is climb high, sleep low: hike to a higher point during the day, then descend to sleep — your body gets practice with thin air and recovers where oxygen is thicker. The corollary is the trekker’s golden rule: don’t go up until symptoms go down. If mild symptoms appear, rest at the same altitude until they clear before gaining more height.
Hydration, Food, and Daily Habits
Dehydration and altitude sickness feed each other, so aim for generous fluid intake — around three to four litres a day is a common trekker benchmark — and watch that your urine stays pale and copious. Eat plenty: altitude suppresses appetite while increasing calorie burn, and a carbohydrate-rich diet is widely recommended for high-altitude trekking. Avoid alcohol, especially in the first days at altitude; it dehydrates you, worsens sleep, and masks symptoms. The same caution applies to sedative sleeping pills, which can depress breathing during sleep. Keep warm, eat well, and don’t trek alone at altitude — a companion can spot the confusion and denial that sometimes accompany altitude illness.
Recognizing Altitude Sickness
Acute Mountain Sickness (AMS) is the common, mild form: headache plus one or more of nausea, dizziness, fatigue, poor sleep, or loss of appetite. It usually improves with rest, fluids, and a pause in ascent. HAPE (fluid in the lungs: breathlessness at rest, persistent cough, extreme fatigue) and HACE (brain swelling: confusion, clumsiness, severe headache) are medical emergencies that can kill within hours. Any worsening symptom at altitude — especially breathlessness at rest, a wet cough, or unsteady walking — means descend immediately and get medical help. People at altitude often deny or fail to recognise their own symptoms, so trek with others and take their word over your own judgment.
Medication: What Diamox Does and Doesn’t Do
Acetazolamide (commonly known as Diamox) is the one medication with solid evidence for preventing AMS — it speeds up the acclimatization process by helping you breathe deeper and faster. Travel-medicine guidance commonly cites a low preventative dose (often around 125 mg twice daily, started before ascent), but it is a prescription drug with real side effects — tingling fingers and lips, increased urination, altered taste — and it must not be taken by people allergic to sulfa drugs. Consult a doctor or travel clinic before your trip; do not buy and dose it on the fly in a trekking town. Crucially, Diamox is preventative, not a cure, and it never justifies ascending faster than your body allows. It also does nothing for HAPE or HACE, for which descent is the treatment.
The Descent Rule
If mild symptoms do not improve after a rest day, or if they get worse at any point, descend — even a few hundred metres can bring dramatic relief. The only genuinely effective treatment for altitude sickness is getting to lower altitude; everything else buys time. Never leave a sick person alone to descend by themselves, and never let summit pressure override symptoms. Mountains will still be there next season; a bad call at altitude is not one you get to retake.
A Note on This Guidance
This article summarises widely discussed trekking-community and mountain-medicine guidance, but it is general planning information, not medical advice. Altitude affects everyone differently, and medication decisions belong with your doctor or a travel clinic — ideally weeks before you fly, not the night before the trek. Plan conservatively, build in rest days, and treat the itinerary as a draft your body is allowed to edit.
Arjun Mehta is the pen name behind Mountains Bliss — practical mountain-travel guides with routes, costs, seasons and safety notes, researched from real trekker discussions and cross-checked before publishing. No sponsored posts, ever.
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