Altitude sickness: what causes it and how to avoid it

Have you ever felt dizzy or had a mild headache while you’ve been at high elevation? This could be a sign of altitude sickness.

More and more travellers are heading to high-altitude regions for activities like skiing, trekking, or mountain climbing, opens in a new tab. As you prepare for your trip, learn the signs and ways to prevent altitude sickness (also known as Acute Mountain Sickness, or AMS). It's an important part of your safety toolkit, both mentally and physically.

What causes altitude sickness?

Altitude sickness typically affects around 20% per cent of people, opens in a new tab at 2,500m, and 40% at 3,000m. It happens because the air thins as you ascend, meaning your body gets less oxygen. Symptoms at the most basic level can be as mild as headaches but can escalate in rare circumstances to being fatal. No one is immune – being extremely fit could actually have a greater impact, for example, as that person might ascend more quickly, opens in a new tab.

Dr Deb Mills runs a specialist travel clinic, opens in a new tab out of Brisbane and says the speed of an ascent is the most important contributing factor to altitude sickness.

“Most people in Australia have no experience of altitude effects because our mountains are not high enough to give symptoms,” she says.

Andrew Lock OAM, opens in a new tab is one of Australia’s most accomplished mountaineers and the only Australian to have climbed all 14 “eight-thousanders”, the mountains with peaks higher than 8,000m. He says high-altitude regions need to be approached with the right mental approach.

“Take the time to immerse yourself in the environment, adapt to it and enjoy it,” he says. “They are not to be rushed.”

In Australia, the highest peak is Mount Kosciuszko at 2,228m. But around the world, high-altitude destinations are becoming more popular and easier to reach, opens in a new tab, including Machu Picchu at 2,430m, Bolivia’s capital La Paz at 3,660m, Everest Base Camp at 5,364m, and Mount Kilimanjaro at 5,895m.

There are also other popular tourist spots that might not seem like high-altitude places. For example, Mexico City is 2,240m above sea level, and most ski resorts, opens in a new tab in Colorado, USA, are more than 3,000m high.

Dr Ivan Parise is an Australian GP with a special interest in travel medicine. He says high-altitude travel can be risky without proper preparation and awareness of altitude sickness.

“Many millions of people each year travel to high altitude, understandably with such beautiful views, interesting cultures and historical cities,” Dr Parise explains. “Climbing in general requires special skills, special preparations and often the involvement of support groups that are well aware of what altitude illness is, how to avoid it and how to treat it.”

Altitude sickness symptoms, opens in a new tab can range in severity. Most commonly, the initial symptoms include:

• headache

• nausea

• poor appetite

• fatigue

• difficulty sleeping

• dizziness

“These symptoms usually start 6-12 hours into the ascent,” says Dr Parise. “If you rest and don’t go any higher, symptoms can dissipate in a day or two. However, if ignored and the ascent continues, it can lead to worsening illness.”

In extreme cases, altitude sickness can cause life-threatening conditions that require urgent medical assistance:

High-Altitude Cerebral Edema (HACE), opens in a new tab or swelling of the brain. It’s rare in travellers under 3,500m. Symptoms include severe headache, unsteadiness, confusion, vomiting or drowsiness.

High-Altitude Pulmonary Edema (HAPE), opens in a new tab or fluid on the lungs, is rare below 4,500m. Symptoms include shortness of breath, cough, chest tightness and weakness. It’s the most common cause of death from altitude illness, opens in a new tab if not treated by an experienced doctor.

Lock's advice is simple and crucial: if you start feeling the symptoms of altitude sickness, stop climbing higher.

“For many people with mild symptoms of AMS, an additional day or two at the same altitude will enable them to acclimatise and continue. If it is more serious, then the cure is descent into higher pressure,” he says.

“It is how we respond to AMS that is critical: rest, rehydrate, acclimatise, descend or evacuate if necessary. If ignored, it will almost certainly worsen.”

For more severe cases like HACE and HAPE, you need to act fast. Climbers should descend immediately, opens in a new tab, aiming for a descent of around 500 - 1,000m, and seek emergency medical help.

While a portable hyperbaric chamber can help by simulating a lower altitude and easing symptoms, it's really just a temporary fix. The priority is to get down to a safer altitude as quickly as possible.

Ascend slowly

Lock’s top tip is to take it slow. “It’s much better to go for a gradual ascent than to rush and risk having to descend and restart your acclimatisation or, even worse, evacuate,” he advises.

“The mantra many mountaineers live by is ‘climb high, sleep low.’”

If you’re heading above 3,000m, try not to increase your sleeping altitude by more than 300-500m a day, opens in a new tab. And remember to take a rest day every three to four nights, opens in a new tab to sleep at the same altitude.

“This helps your body keep adapting while you’re at a safer altitude,” Lock explains.
“Altitude can be deadly, and the mountains are massive,” he adds. “So, make sure you understand the ascent process and be patient with your climb.”

Rest and hydrate

To help your body adjust to high altitudes, take a couple of days to rest before you start your climb. Keep your hydration up, opens in a new tab, and steer clear of alcohol, caffeine, and other stimulants. Once you arrive at high altitude, give yourself 48 hours to acclimate, opens in a new tab. This will help you handle the lower oxygen levels and make your ascent smoother.

Be prepared

“As with all travel, it’s strongly recommended to find out all you can about health hazards overseas, so the holiday of a lifetime does not turn into the trip you want to forget,” Dr Mills reminds us.

Before your trip, talk to your GP about medications for altitude sickness, opens in a new tab They might suggest over-the-counter options like ibuprofen to help with headaches.

Make sure you’re physically ready for your adventure. Discuss your fitness level with your doctor, be honest about your skills, and plan for any medical needs during your trip. Make sure you’re prepared in case you need medical help with travel insurance for overseas medical expenses, opens in a new tab.

Travelling soon? Consider nib Travel Insurance and get a quote, opens in a new tab.

To learn more about what’s covered, see nib travel insurance, opens in a new tab. Nib Health insurance members get a 10% discount off their travel insurance.*

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