What is altitude sickness? And can I prevent it?

This is an important question that's asked often by those preparing to go on a high-altitude trek.

At its simplest, altitude sickness is your body reacting badly to the lower oxygen intake associated with a very high or higher altitude. It usually strikes from anywhere over 3,000 m (9,000 ft) above sea level.

Many trekkers develop mild altitude sickness, also known as acute mountain sickness (AMS). Such folks can experience symptoms like a headache, fatigue even when resting, nausea, vomiting, lightheadedness, breathlessness, loss of appetite, muscle aches, vivid dreams, and insomnia or interrupted sleep. Usually AMS isn't a worry in itself – it's more unpleasant than anything else. The main thing is to monitor it to ensure it doesn't develop into moderate or severe altitude sickness.

The next level of intensity is moderate altitude sickness, which can cause high altitude pulmonary oedema (HAPE), which is where your lungs fill up with fluid and you start coughing and spluttering. You need urgent medical attention if you develop HAPE as it can kill you quite quickly.

The most severe form of altitude sickness causes high altitude cerebral oedema (HACE), which is a build up of fluid in the brain, causing it to swell. This also needs urgent medical intervention or it can kill you.

You can keep trekking if you only have AMS, but if it develops into moderate or severe altitude sickness then you need to stop trekking immediately and seek medical attention.

Many folks who develop mild altitude sickness keep trekking. Though be careful if you're trekking to an even higher elevation as this could tip the scale and make things worse. But if you feel able to push through the unpleasant symptoms of AMS, then have at it!

However, if your AMS develops into moderate or severe altitude sickness, then you need to descend to a safe altitude immediately. It will depend on your condition if you hike down in altitude yourself or if you need to be evacuated via pack animal, stretcher or helicopter.

With this in mind, it's critical that you only trek with comprehensive travel insurance to ensure that you can be evacuated by air should that option exist and be the quickest way of transporting you out of the high elevation zone. You also want to know that your policy will cover any possible hospitalisation.

The best thing you can do for yourself is to trek with an experienced guide who's a certified wilderness first aider. These folks are very experienced in detecting the symptoms of altitude sickness and knowing when it's safe to keep pushing ahead and when it's advisable to turn back (in other words, descend in altitude).

We would always encourage you to take your trek guide's advice in such matters, even if that advice is disappointing in terms of not completing your adventure. Remember, advanced altitude sickness can be very dangerous.

High-altitude trek guides are trained to detect altitude sickness

By far the best way to prevent altitude sickness is to never leave the coast. But who wants that life? Adventure awaits, and you definitely should go high-altitude trekking if you hear the mountains calling your name.

There’s no surefire way to prevent yourself developing altitude sickness. The illness is no respecter of age nor fitness, and seemingly strikes at random.

That said, there are some things you can do to help minimise your chances of developing altitude sickness, or at least minimise the intensity of the symptoms ...

As discussed, the cause of altitude sickness is ascending too rapidly into a very high altitude zone. Whatever the trek or other high-altitude adventure you intend to tackle, do your homework in terms of determining a safe route or itinerary that will give your body enough time to adjust to each new bump in elevation. Look for advice from past trekkers as well as from tour operators with a good safety record in that region.

Often it's a good plan to have a rest day or two in your trek, or to allow for wiggle room so that you can take a rest day should you feel the need for one arise. Also take note that dropping down a little in elevation (by a few hundred metres at least) during your ascent into high altitude can really help your body to acclimatise (adjust) well.

So if you have a nine-day upwards high-altitude trek planned, for instance, you might want to consider incorporating one or two rest days, as well as see if there's a route you can walk that drops down a little in elevation for a night or two.

Finally, a word of advice: don’t opt for a too-short trek route because it saves you the expense of an extra day, or similar. Remember, you’re investing in a potentially life-enhancing adventure, and trying to reduce costs by cutting down on your days could mean you develop altitude sickness and consequently don’t end up summiting or completing your trek.

It's a very good idea to visit your doctor before embarking on a high-altitude adventure. In fact, a GP visit before any type of international travel is always a good idea.

Speak to your GP about your high-altitude plans. He or she might be able to prescribe you an altitude medication (like acetazolamide) that can lessen the intensity of some of the symptoms of AMS. You also want to discuss any possible complications that could arise in terms of your personal medical history.

Your doctor might also like to prescribe you some backup medications should you develop a more intense form of AMS. We're talking things like a corticosteroid should you start coughing and spluttering or an antiemetic medication should you start to suffer from terrible nausea. These can be good-to-haves since often high-altitude treks take place in regions far from hospitals and pharmacies.

Drinking plenty of clean water helps your body to acclimatise better, and also ameliorate the unpleasant symptoms of AMS. So be sure to carry at least three litres of water for each day, and try to take small sips often. Don't wait till you feel thirsty before drinking.

We hope that was helpful. If you're looking for your next high-altitude adventure, you might enjoy reading 15 of the world's best high-altitude treks.