Altitude Sickness and Acclimatization

Trekking The Inca Trail Trek often means going to high altitude. It is important that you understand the risks of high altitude and take the right precautions to acclimatize properly.

We have written a detailed guide on acclimatization and altitude sickness which we highly recommend you read.


Most mountainous treks and climbs will ascend to “high altitude” points, which obviously come with certain altitude sickness risks.

Understanding these risks is the key to ensuring your safety and will give you the knowledge to deal with altitude sickness symptoms and its severe variants

  • High Altitude Cerebral Edema (HACE) and
  • High Altitude Pulmonary Edema (HAPE)

In this article on acclimatization and altitude sickness we have provided general information on acclimatization and a full outline on altitude sickness, HACE and HAPE, as well as set out best practice information on preventative medications like Diamox.


Acclimatization is a process that results in the body becoming accustomed to lower levels of oxygen at altitude. It is only achieved by spending extended periods of time at various levels of altitude before progressing higher.

The trekkers typically refer to three main levels of altitude. The first level, aptly called “high altitude”, describes the altitude zone between 2,500m and 3,500m. Altitudes between 3,500m and 5,000m are referred to as “very high altitude”. The third level is called “extreme altitude” and is characterized by zones above 5,000m.

When it comes to trekking at altitude, most people can ascend from sea level (say your hometown) to 2,400m without experiencing altitude illness symptoms. Once you get beyond this height though, changes in oxygen and pressure levels begin influencing the body’s physiology.

To illustrate these changes consider the following. At sea level oxygen air saturation is about 21 per cent and barometric pressure is approximately 760mmHg (millimetres of mercury). As one ascends oxygen saturation stays about the same but air density decreases, which means the percentage of oxygen per breath reduces. You can imagine this as oxygen molecules moving further and further away from each other at higher altitudes, hence the term “thin air”.

The good news is that as oxygen per breath decreases, the body very quickly and cleverly starts to adapt to the new environment. Four main changes occur. Firstly, breathing becomes a lot faster and deeper (even at rest). Secondly, blood concentration changes – red blood cells, the part of your blood responsible for carrying oxygen, increases. The third change occurs in your lungs and is a result of increased pressure in your pulmonary capillaries. This forces blood into areas of the lungs that are not used when breathing at sea level. The final change involves the secretion of an enzyme that promotes more effective transfer of oxygen from your hemoglobin to your blood tissue.

With these changes and, assuming you have given yourself enough time to rest at a “reasonable” starting altitude, the body will acclimatize. Progressing to higher altitudes on a slow and incremental scale thus becomes possible.

To demonstrate acclimatization in action, trekkers and mountaineers have come up with a term called the acclimatization line – an arbitrary altitude line that describes the point at which someone’s altitude sickness symptoms appear.

For instance, let’s assume that your altitude line is around 3,000m. On the first day of your trek you ascend to 3,000m and remain asymptomatic as you are on or just below your acclimatization line. Resting at this altitude for a night or two should ensure that you are fully acclimatized to this altitude and your line might move to around 3,800m. Trekking to 3,700m will ensure you remain asymptomatic, but if you continued further to say, 4,000m, it is likely that you will start experiencing altitude illness symptoms. Descent back down to below your acclimatization line (in this example, 3,400m) to rest for a few days should resolve any symptoms. Continued ascent would only result in the deterioration of your condition.

So what is the learning? If you want to acclimatize properly make sure you build in rest days as you ascend, make sure to take note of your altitude if symptoms present themselves. Near your acclimatization line altitude sickness symptoms typically resolve after a day or two, but continued ascent before you have properly acclimatized will almost certainly lead to the worsening of your symptoms and further acclimatization will not occur. The only sure way to improve is to get below the altitude line where your symptoms first occurred.

Altitude Sickness Symptoms

Altitude illness (Acute Mountain Sickness (AMS) or altitude sickness), is a condition caused by fast ascents to high altitudes. Susceptibility to altitude sickness increases for most people at around 3,000m some can experience altitude illness symptoms as low as 2,400m.

There is little in the way of identifying whether you are susceptible to altitude sickness as there is no correlation between age, fitness, health, gender, or indeed previous experiences of going to high altitude. What we are sure about is that climbing more than 500m a day from 2,400m increases the probability of altitude illness; exerting yourself at high altitude and dehydration also exacerbates symptoms.

Additional Tips To Follow for the Inca Trail Treks

  • On your trek make sure to build in acclimatization days where you relax and drink lots of fluids
  • Ensure you remain very well hydrated on the trail – drink two to three liters of water a day
  • Go slowly and don’t over-exert yourself
  • Avoid alcohol, smoking and stimulants whilst trekking
  • Work with a respectable operator or guide who understands the risks of altitude illness and is trained / has the equipment to deal with any potential problems
  • Try to ascend in small increments of 500-700 meters a day, this can include trekking high (say 1,000m up) to sleep low (600m from the start point from that day)
  • Consider taking a preventative medication like Acetazolamide (Diamox) as an extra precaution – see below

Prescribed Medication – Diamox

Diamox, clinically known as Acetazolamide, is a prescription drug that effectively helps mitigate altitude illness. It is a preventative medication (aka a prophylactic), and not a cure. This means that it helps with promoting faster acclimatization and thus prevents the potential onset of altitude illness, but does not cure it.

Depending on where you live in the world you may need to get a doctor’s prescription, but more often than not it can be bought over the counter at a pharmacy. We recommend you consult your doctor before using it. The drug should not be taken by pregnant women or people with kidney and liver issues.

Side effects of the drug include frequent urination; taste alterations; numbness and tingling in toes, finger and nose; and drowsiness, nausea and vomiting. Many of these side effects can be misdiagnosed as altitude illness. To avoid confusion we recommended that you take a short dose of Diamox a few weeks before departing for your trek to test if you experience any side effects.

Diamox is usually sold in a 250g tablet. Most hikers take 125g in the morning and the remaining 125g in the evening, starting one day before starting a trek and finishing on the day one returns to the trek start point.

In our opinion we think it is worthwhile taking Diamox as a preventative measure if you plan to do a trek that goes above 5,000m but recommend consulting your doctor before you do so.