Altitude sickness

Altitude sickness can happen when you are at high altitude or during a rapid ascent if your body is not adequately acclimatised to the conditions. The cause is the reduced oxygen content in the air, which leads to lower oxygen levels in the blood and can result in symptoms. The body needs time to adjust to the decreased oxygen levels (acclimatisation). The higher the altitude or the quicker the ascent, the greater the risk of altitude sickness. Symptoms are more likely to appear above 2,500 metres; however, susceptibility can vary from person to person, meaning some individuals may experience symptoms at lower altitudes, while others may not develop any symptoms even at high altitudes.

When can altitude sickness occur?

Typically, symptoms occur at altitudes above 2,500 metres.

What are the symptoms?

Symptoms usually manifest a few hours to a day after reaching a high altitude. The following symptoms may occur:

• Headache
• Nausea and/or vomiting
• Difficulty sleeping

• Dizziness and/or weakness

On average, these symptoms last for a few days. The condition is benign, provided you do not ascend further while experiencing them. Mild altitude sickness can progress to severe altitude sickness. This is characterised by worsening headache and shortness of breath, even at rest and particularly at night. Individuals may become so fatigued that they require assistance with eating and dressing. Severe altitude sickness requires you to descend immediately. If left untreated, altitude sickness can lead to fluid accumulation in the lungs and brain (pulmonary and cerebral oedema), which can result in coma and death.

How to prevent altitude sickness?

Several strategies can help prevent altitude sickness. For instance, it is important to acclimatise properly when you are in an area above 1,500 metres. For altitudes between 1,500-2,500 metres, it is recommended to stay at least two nights at that elevation. If you fly directly to 2,500 metres or higher, it is best to remain at that altitude for several days before proceeding.

Additionally, acclimatisation can be facilitated by limiting exertion and by climbing higher during the day than you sleep at night (climb high, sleep low). Avoid heavy physical activity for the first two days above 2,500 metres.

When above 3,000 metres, it is advisable not to ascend more than 500 metres each night you are there. When ascending more than 500 metres, spend at least two nights at the same altitude. Maintaining a flexible itinerary allows for rest days in case altitude sickness occurs.

It is crucial to stay well-hydrated, aiming for several litres each day to keep urine light and clear. The use of alcohol and sleeping aids is discouraged.

To promote acclimatisation, medication may be prescribed such as acetazolamide (Diamox®). Always read the patient information leaflet before use. The medication should be taken to prevent altitude sickness. Start it 24 hours before reaching 3,000 metres and continue until two days after reaching your highest altitude.

If you have a heart or lung condition, consult your doctor for personalised advice to ensure you are well-prepared for your trip.

More information

Mild altitude sickness: do not ascend further. Start with acetazolamide. Descend if symptoms do not improve within a day. For headache relief, paracetamol can be used. Anti-nausea medication may help with nausea. Once symptoms have lessened, you may cautiously continue your ascent.

Severe altitude sickness: descend immediately and seek medical assistance (including oxygen and medication). Keep in mind that access to medical care is limited in remote areas!