Altitude Sickness: Symptoms, How to Prevent It and When You Must Go Down

Fitness does not protect you from altitude sickness. Marathon runners get it. Teenagers get it. People who were fine on their last trip get it. What protects you is how fast you go up, and knowing when to come down.

Imagine flying straight into Cusco, Peru, at about 3,400 metres. You feel fine at the airport. By evening you have a pounding headache, you feel sick, and you can’t sleep. Your friend says it’s just the flight. The next morning, a guide asks how you slept, takes one look at you and tells you to rest today instead of hiking. That guide knows something every traveller should.

Who gets altitude sickness?

Altitude sickness can affect anyone who goes above about 2,500 metres (8,000 feet), especially if they go up quickly. Popular places at that height include Cusco and the Inca Trail, La Paz, Quito, Lhasa, parts of the Alps and Rockies, and treks to Everest Base Camp or Kilimanjaro. Your risk is higher if you’ve had it before, if you ascend fast, or if you sleep high on your first night.

The three types

• Acute mountain sickness (AMS): the common, mild form. Headache plus one or more of nausea or vomiting, tiredness, dizziness, loss of appetite or poor sleep. It usually starts 6 to 12 hours after arriving.
• High altitude cerebral oedema (HACE): swelling of the brain. Severe headache, confusion, strange behaviour, drowsiness and clumsiness, such as being unable to walk in a straight line.
• High altitude pulmonary oedema (HAPE): fluid in the lungs. Breathlessness even at rest, a cough (sometimes with frothy or pink phlegm), chest tightness and extreme tiredness.

HACE and HAPE are life-threatening and can develop quickly.

How to prevent altitude sickness

• Go up gradually. Above 3,000 metres, aim to increase the height where you sleep by no more than about 500 metres a day.
• Build in rest days: one every three to four days, with no gain in sleeping height.
• “Climb high, sleep low”: day hikes higher are fine, but return lower to sleep.
• Avoid alcohol and sleeping tablets for the first couple of days.
• Drink enough fluid, eat regularly and take it easy on arrival.
• Ask about medication. A doctor may prescribe acetazolamide to help prevent altitude sickness if you can’t ascend slowly or have had it before. Discuss this at a travel clinic before you go.

But when do you have to go down?

Follow three simple rules:

1. If you feel unwell at altitude, assume it is altitude sickness until proven otherwise.
2. Never go higher with symptoms. Rest at the same height until they’ve gone. Simple painkillers and anti-sickness medicine can help mild AMS.
3. If symptoms get worse, or any sign of HACE or HAPE appears, go down immediately, even at night, and get medical help. Descending even 300 to 1,000 metres often brings rapid improvement. Never let someone who is unwell descend alone.

Check your travel insurance covers trekking at your planned altitude and emergency evacuation.

Sources: US Centers for Disease Control and Prevention (CDC Yellow Book: High-altitude travel), NHS (Altitude sickness), Wilderness Medical Society clinical practice guidelines. This guide is for general information and does not replace advice from your own nurse, doctor, travel clinic or pharmacist.