Reviewed by The Wellness Team. Last reviewed October 2026.
Altitude sickness is common, unpredictable and largely preventable with the right ascent plan. It can affect anyone above about 2,500 metres, fit or unfit, and it catches out trekkers, skiers and even people flying straight into high cities such as Cusco, La Paz or Quito. As of October 2026, the single biggest factor in avoiding it is how fast you climb, not how fit you are. Planning a high-altitude trip? Message us on WhatsApp and a doctor can review your itinerary and your risks before you go.
How do I know if I will get altitude sickness?
You cannot know for certain in advance, and fitness does not protect you. The best predictor is a previous episode: if you have had altitude sickness before at a given height, you are likely to get it again at a similar height on a similar schedule. First-time trekkers above 3,000 metres should assume they are susceptible and plan accordingly.
The early symptoms feel like a bad hangover and typically start 6 to 12 hours after arriving at a new height:
- Headache (the hallmark symptom)
- Nausea, poor appetite or vomiting
- Dizziness and unusual fatigue
- Poor sleep
A headache plus any one of the others at altitude is altitude sickness until proven otherwise. Mild symptoms at a new sleeping height mean one thing above all: do not go higher until they have gone.
How do I prevent altitude sickness?
Ascent rate is the lever that matters most. As of October 2026, the Wilderness Medical Society guidelines recommend:
- Above 3,000 metres, increase your sleeping altitude by no more than about 500 metres per day
- Take a rest day (no further ascent) every 3 to 4 days
- Climb high, sleep low where the route allows
- Avoid alcohol and heavy exertion in the first 48 hours at height
For some itineraries, for example flying straight into a high city or a rapid trek such as Kilimanjaro's shorter routes, a doctor may recommend preventive medication started before ascent. Whether that is appropriate depends on your medical history, your previous altitude experience and how fast the itinerary forces you to climb, so it needs an individual assessment rather than a blanket yes. WhatsApp us with your route and we will review it with you before you fly.
When is altitude sickness an emergency?
Most altitude sickness stays mild and settles with rest at the same height. Two forms are life-threatening and need immediate descent:
- High altitude cerebral oedema (HACE): confusion, loss of coordination, unsteady walking, drowsiness, behaving strangely. An unsteady heel-to-toe walk at altitude is an emergency.
- High altitude pulmonary oedema (HAPE): breathlessness at rest, a persistent cough sometimes with frothy or blood-stained sputum, chest tightness, extreme weakness.
The treatment for both is descent, immediately, even at night. Oxygen and specific treatments help in resort or clinic settings, but nothing replaces going down. Anyone with these symptoms should not be left alone.
Can an online GP help before a high-altitude trip?
Yes, and before is the right time. A pre-travel consultation reviews your itinerary against safe ascent rates, your medical history (heart and lung conditions, pregnancy and previous altitude illness all change the advice), what to carry, how to recognise danger signs in yourself and your group, and whether preventive medication makes sense for you. If you are travelling for a trek or expedition with specific requirements, we can also help with travel health and fitness-to-fly certificates and the wider travel clinic planning around your trip.
As of October 2026, a phone consultation with The Online GP costs £59, a video consultation costs £150, and an in-person appointment at 10 Portman Square, Marylebone costs £220. Message us on WhatsApp and you can usually speak to a doctor the same day.
Frequently asked questions
At what height does altitude sickness start?
Symptoms are possible from about 2,500 metres, and become common above 3,000 metres, which includes most major trekking routes and ski resorts. The risk rises steeply the faster you gain height.
Does being fit protect me?
No. Fitness helps you climb faster, which can actually increase risk by encouraging rapid ascent. Young, fit men are statistically among the more likely groups to get into trouble, partly because they push on through early symptoms.
How long does altitude sickness last?
Mild symptoms usually settle within 24 to 48 hours if you stop ascending. If they do not, or they worsen, descend. Most people then acclimatise and can continue carefully.
Is it safe to sleep at a height where I have symptoms?
A mild headache on arrival at a new sleeping height is common. If symptoms are more than mild, worsening, or include vomiting, poor coordination or breathlessness at rest, that height is not safe to sleep at. Descend.
I only have a week. Is a fast Kilimanjaro or Everest Base Camp itinerary safe?
Shorter itineraries carry meaningfully higher altitude sickness rates because they compress acclimatisation. If your time is fixed, book a pre-travel review: route choice, an extra acclimatisation day built in where possible, and an individual prevention plan make a real difference.
Sources: Wilderness Medical Society clinical practice guidelines for the prevention, diagnosis and treatment of acute altitude illness; UIAA Medical Commission advice for travellers at altitude; NaTHNaC travel health guidance on high altitude travel.
Reviewed by The Wellness Team.