High-Altitude Travel: Plan, Prevent and Recognise Altitude Sickness

Altitude sickness is the main health risk on a high-altitude trip, and the single most effective thing you can do is to gain height slowly. The NHS says you can get altitude sickness above roughly 2,500 metres, and that you are more likely to get it if you travel or climb to a high altitude quickly. The CDC adds that any unacclimatised traveller heading to a sleeping altitude of 2,450 metres or more is at risk. Most cases improve with rest in one to three days, but it can become life-threatening and need treatment.

Who this affects

Altitude sickness can affect anyone who goes high, including fit, trained travellers. The CDC states that training and physical fitness do not affect risk, that children are as susceptible as adults, and that people over 50 have slightly less risk. Susceptibility is partly genetic, and there is no simple screening test to predict it. A traveller's sex plays a minimal role, if any, in determining predisposition. The goal for the traveller might not be to avoid all symptoms of altitude illness but to have no more than mild illness, thereby avoiding itinerary changes or the need for medical assistance or evacuation. You cannot get altitude sickness in the UK.

How you responded to altitude before is the most reliable guide for future trips, but only if the altitude and rate of ascent are similar, and even then it is not infallible. Travellers who have successfully adjusted to an altitude are at risk when moving to higher sleeping altitudes, especially if the altitude gain is 600–900 metres. The CDC lists common high-altitude destinations including Cusco in Peru (about 3,350 metres), La Paz in Bolivia (about 3,650 metres), Lhasa in Tibet (about 3,700 metres), Everest base camp in Nepal (about 5,400 metres) and Mount Kilimanjaro in Tanzania (about 5,900 metres). The NHS also names Mount Everest, Mount Kilimanjaro, some places in the Alps and La Paz. The UK government's Peru travel advice notes that altitude sickness is a serious risk in parts of Peru, including Cusco, Puno, the Colca Canyon and Kuelap.

Some itineraries carry more risk than others. The CDC says flying directly to destinations above about 3,400 metres puts travellers in a high-risk category for acute mountain sickness, with rates approaching 50% in those situations. On trekking routes such as Everest base camp, prevalence can approach 30% even on standard acclimatisation schedules.

What to do step by step

1. Plan your ascent before you book. The CDC advises avoiding a jump from low altitude (1,200 metres or below) to a sleeping altitude of 2,750 metres or more in one day. The NHS says try not to travel from below 1,200 metres to above 3,500 metres in one day. The NHS also advises spending a few days at an altitude below 2,500 metres before going any higher. A high-altitude exposure (>2,750 m) for ≥2 nights, within 14 days before the trip, is useful but closer to the trip departure is better.
2. Stage the climb. The CDC says acclimatising for at least 2 to 3 nights at around 2,450 to 2,750 metres before going higher is markedly protective against acute mountain sickness.
3. Limit daily sleeping gains. Once above 3,000 metres, the CDC recommends moving sleeping altitude by no more than 500 metres per day and adding an extra night for every 1,000 metres of sleeping altitude gain. The NHS gives the same 500-metre sleeping rule above 3,000 metres.
4. Take rest days. The NHS advises a rest day at the same altitude every 3 to 4 days at 3,000 metres or more.
5. Avoid direct flights to altitude if you can. The NHS says try not to fly directly to a high-altitude place; if it is unavoidable, rest for one day before going higher. The CDC notes that in places such as Cusco and La Paz, travellers can sleep 1 to 2 nights lower than the airport before starting their ascent.
6. Keep the first 48 hours easy. The CDC advises only mild exercise for the first 48 hours and avoiding alcohol for the first 48 hours. The NHS says do not drink alcohol while travelling or climbing. If you normally drink caffeine, the CDC suggests continuing, to avoid a withdrawal headache that could be mistaken for an altitude headache.
7. Drink enough water. The NHS lists staying hydrated as a way to reduce risk.
8. Speak to a GP or travel clinic before you go, especially if you have had altitude sickness before or are travelling to altitude quickly. The NHS says they may prescribe medicine to help prevent it. The CDC suggests considering acetazolamide to speed acclimatisation if abrupt ascent is unavoidable.
9. If symptoms start, stop climbing. Tell someone you are travelling with, rest at the same altitude, and do not go higher. The NHS says you can take anti-sickness medicine or painkillers such as ibuprofen or paracetamol to ease symptoms. If your symptoms have gone and you feel better, you can travel or climb to a higher altitude.

Costs and timing

The main cost is time in your itinerary. Extra nights at intermediate altitude are the cheapest form of prevention, and the CDC notes that adding extra days to a trek can make it safer and more enjoyable. Build those nights into your plan before you book flights and lodges.

Medication is a decision for a clinician, not a self-service purchase. The CDC describes three risk levels: at low risk, acetazolamide prophylaxis is not indicated, but travellers should carry over-the-counter painkillers for headache and have acetazolamide to speed acclimatisation or treat early acute mountain sickness; at medium risk, acetazolamide prophylaxis would be beneficial and should be considered, with dexamethasone considered for emergency use; at high risk, acetazolamide prophylaxis is strongly encouraged and dexamethasone should be carried for emergency use. The NHS says a GP or travel clinic may prescribe preventive medicine if you have had altitude sickness before or are going high quickly.

Sort this out weeks before departure, alongside your other pre-travel checks. For Peru, the UK government advises checking vaccine recommendations and health risks at least 8 weeks before your trip, and notes that medical treatment is not easily available and can be harder to access outside Lima. It also advises making sure you have appropriate travel insurance and accessible funds to cover treatment abroad and repatriation.

Exceptions and special situations

The CDC notes that travellers with compromised lung function must be cautious, and that all travellers should avoid respiratory depressants. It also advises that people with chronic illnesses, those dependent on electronic devices, those who have difficulty walking or who are medically frail are likely not good candidates for adventure travel. If you have a heart, lung or other long-term condition, or you are pregnant, discuss the trip with a clinician before booking. Travellers might need medical clearance to participate in a trip. For travellers with chronic diseases, healthcare professionals should carefully consider medical clearance and provide prescriptions for regular medications. Screen travellers for conditions that can be exacerbated by environmental hazards or exertion. Check for a history of anaphylaxis-level allergies, asthma, cardiac disease, deep vein thrombosis and pulmonary embolism, diabetes, joint replacement, opioid-dependent pain, oxygen-dependent emphysema, recent surgery, sleep apnea, or stroke. Travellers with a previous history of environmental illness could be at risk for recurrence. Counsel travellers to carry electronic copies of their most recent electrocardiogram and chest x-ray, their medical and surgical history, and a medication list. Blood type may be useful to know for trips in extremely remote locations or long expeditions. Caution travellers who rely on battery-operated devices about the possibility of device failure or lack of electricity and discuss the need for a backup plan or the possibility that they should avoid adventure travel altogether. Some people with chronic illnesses, especially those who are medically dependent on electronic devices, who have difficulty ambulating, or who are medically frail, likely are not good candidates for adventure travel. Adequate hydration, nutrition, and sleep could be in short supply, especially with increased demands due to exertion, terrain, and weather. During the planning stages, travellers should pay attention to how they will obtain food, rest, and water on their journey.

Children are as susceptible as adults. Older travellers are not protected either, though risk is slightly lower over 50.

Adventure trips bring their own planning needs. The CDC advises travellers on guided trips to ask organisers about emergency contingency plans, guide experience and medical training, recommended medications and supplies, medical kits and safety equipment carried by guides, and recommended insurance. It warns that having insurance does not guarantee rescue, that you may need to pay up front for rescue, evacuation and repatriation, and that policies often exclude wilderness rescue and activities such as mountaineering and skiing unless you add a rider. Insurance comes in many forms and is widely variable; having insurance does not guarantee rescue. Warn travellers that they might need to pay in advance for rescue, evacuation, and repatriation, especially for aeromedical transport from remote locations, so they should bring a credit card with a high credit limit and emergency cash. Insurance coverage can be contingent on deductibles, maximum expenditures, medical control approval, and preexisting conditions. Insurers also might not authorize aeromedical transport. Insurance companies might deny claims involving acts of war or civil unrest, alcohol or drugs, chronic illness, mental health, and pregnancy. Travellers should read policies carefully before purchasing insurance and departing on their trip. Types of travel insurance important for adventure travel: comprehensive expedition policies can include travel, medical, rescue, repatriation, and security services. Domestic health insurance might or might not be effective outside a home country. Often, travellers need to pay up front for medical care and get reimbursed from health insurance providers once they return home. Short-term rescue insurance is available in some destination countries through local helicopter rescue companies, mountaineering clubs, and ski resorts. Travel insurance, which often includes medical, trip cancellation, evacuation, and repatriation benefits, might exclude coverage for wilderness rescue and adventure sports like diving, mountaineering, and skiing. An adventure sports rider is available with some travel insurance policies. Wilderness rescue insurance policies are available through specialty clubs, outdoor and professional associations, and organizations. If travellers have time, they should consider completing basic life support and first aid courses before departure. Travellers should always keep their credit cards, immunization records, money, passport, and other documents on their person because they might need to seek medical care or evacuate urgently without their luggage. Travellers also can store backup copies as a PDF or JPG format.

What is not yet confirmed

Altitude thresholds and ascent advice come from established official guidance and are not expected to change. One date to note: the NHS altitude sickness page was last reviewed on 31 July 2023 and its next review is due on 31 July 2026, so check the page again before you travel in case the advice has been updated. For country-specific risk, use the TravelHealthPro website, which the NHS recommends for checking travel risk.

This is general guidance only. Ask a doctor, pharmacist or travel clinic about your own situation, ideally weeks before you travel.