How High Can You Climb Before You Need Oxygen?

Some people see the use of supplemental oxygen in high altitude climbs as cheating or taking the easy way out. But at the same time, a low level of oxygen is dangerous to our body. At what point do we go from pushing our own limits to pushing ourselves over the edge? I decided to find out.

So how high can we climb before we need oxygen? 26,000 feet (8,000 meters) is the official ‘Death Zone’ where severe altitude sickness occurs without the use of supplemental oxygen. The body begins shutting down, eventually leading to death. However, oxygen might even be required at lower altitudes of 8,000 to 12,000 feet (2,500 to 3,500 meters) where mild to moderate altitude sickness can begin to set in.

Deciding whether you require oxygen for your climb often goes beyond looking at the elevation of the mountain. There are other factors to consider which may affect when you may experience the effect of altitude sickness.

You Need Oxygen When Moderate Altitude Sickness Sets In

Most people will agree that supplemental oxygen should be used at the ‘Death Zone’ of 26,000 feet (8,000 meters). However, altitude sickness can set it at a much lower altitude, and depending on each individual, you should start using oxygen when you experience moderate altitude sickness.

This is of course based on experience, and a key reason to include high altitude climbing as part of your training routine. For example, if you are planning to climb a mountain above 12,000 feet (3,500 meters), do include some climbs to a lower mountain of 8,000 feet (2,500 meters) to check your susceptibility to altitude sickness.

Altitude sickness ranges from mild to severe, and these can occur at different altitudes for different people. It is crucial to take note of your body condition and look out for when you are exhibiting symptoms of moderate to severe altitude sickness. These symptoms worsen over time, may not respond to medication and often oxygen is required to alleviate them.

Mild altitude sickness (also known as Acute Mountain Sickness (AMS))

  • Symptoms include a headache, difficulty sleeping, nausea, dizziness, fatigue, shortness of breath, loss of appetite, and a general loss of energy.
  • Symptoms usually begin within 12 to 24 hours of arriving at a high altitude.
  • Mild forms of altitude sickness can often go away with rest within a day or two as you get used to the altitude, so it’s doubly important that you give yourself time to acclimatize before a climb and access your own body conditions.

Moderate altitude sickness

  • Symptoms are more intense and are not relieved by over-the-counter medicines.
  • Fatigue, weakness, and shortness of breath worsen instead of improving over time.
  • Confusion, loss of coordination, difficulty walking, worsening headache that is not relieved by medicines, nausea, and vomiting, and tightness in the chest. Normal activity is difficult, although you may still be able to walk on your own (might be staggering).

Severe altitude sickness

  • Symptoms include shortness of breath at rest, coughing (might be with frothy spit), noisy breathing (gurgling or rattling sounds), fever. This is a sign of High altitude pulmonary edema (HAPE) where there is a dangerous build-up of fluid in the lungs
  • Confusion, extreme fatigue, Inability to walk, severe headache, vomiting, and lethargy. This is a sign of High altitude cerebral edema (HACE) where there is is a build-up of fluid in the brain.
  • gray, pale or bluish skin tone, lips or fingernails.
  • Severe altitude sickness is an emergency situation and can be fatal within hours. You must be brought to a lower altitude immediately.
Learn how to keep yourself safe in the mountains with these helpful guides:

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– How To Improve Sleep When Climbing At High Altitude
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What Causes Altitude Sickness

Altitude sickness is caused by the lower oxygen levels at high altitude which in turns causes a lack of oxygen in your body.

The lack of oxygen causes a cascade of effects on your body:

  • Your breathing increases as it tries to get more oxygen
  • Physical activities become more strenuous as your muscles do not have sufficient oxygen
  • Your appetite decreases as your body redirect energy to other key functions instead of digestion. Food also doesn’t get absorbed as efficiently
  • The lack of calories causes further fatigue
  • You get frostbite more easily in your fingers and toes as blood flows towards your key organs
  • Sleeping becomes difficult which again causes further fatigue

This accumulation of negative effects eventually leads to severe altitude sickness and potentially causing death.

Factors Affecting Your Ability To Climb Without Oxygen

There are several factors which determine how our body reacts to the lack of oxygen and the onset of altitude sickness.

Time Spent On Acclimatization

The typical concentration of oxygen at sea level is about 20%, and this drops to 7% at 29,000 feet (9,000 meters) above sea level. This means that you are taking in less oxygen in each breath that you take at a higher altitude as compared to sea level.

In the short term, your body compensates by breathing faster and harder.

In the longer term, your body starts to produce more red blood cells to transport more oxygen to your body. This is what happens when climbers talk about acclimatization — giving time to your body to adjust and adapt to the lower oxygen levels in the air by producing more red blood cells in your body.

The longer time you give yourself to acclimatize, the less you would feel the effect of breathing at high altitudes. By acclimatizing, you can delay the onset of altitude sickness, and can climb to higher altitudes before you require oxygen.

Avoid ascending faster than 1,600 feet (500 meters) per day to allow your body to adapt. If you go above 10,000 feet (3,000 meters), only increase your altitude by 1,000 feet (300 meters) per day.

Your Typical Environmental Conditions

If you are living in a high altitude area, your body will naturally be acclimiatized.

This is why sherpas living in the high altitudes regions of Nepal are better adapted to climbing Mount Everest. Having lived in a high altitude environment, their bodies are used to operating at low oxygen levels (by producing more red blood cells) and altitude sickness is not a big deal for them as it is for people living at lower altitudes.


Unfortunately, genetics have a role to play in a person’s susceptibility to altitude sickness. Some people may be more prone to the effects of altitude sickness, and thus unable to quickly and efficiently acclimatize to high altitude.

Amount Of Time Spent At High Altitudes

Although spending a long time at high altitudes help you to acclimatize, it might not always be the best thing to do.

If you are already experiencing moderate altitude sickness, you should reduce further exposure to low oxygen levels by returning to lower altitudes as soon as possible.

There’s a mantra among climbers that says “Climb High and Sleep Low”. If you climb more than 1,000 feet (300 meters) in a day, returning to sleep at a lower altitude will help prevent altitude sickness.

Taking Preventive Medications

There are some medications that can prevent the onset of altitude sickness. It is crucial to seek the advice of your doctor before taking any medications or drugs at high altitudes.

Acetazolamide (Diamox)

  • Acetazolamide is a medication that allows you to breathe faster and minimize the symptoms caused by low levels of oxygen.
  • It also improves sleep at high altitude by decreasing periodic breathing.

Dexamethasone (a form of steroid)

  • Dexamethasone is a prescription medication that reduces  brain and other swelling caused by altitude sickness.

Just How Much Oxygen Is There At High Altitudes

The concentration of oxygen drops from 20% at sea level to 29,000 feet (9,000 meters) above sea level.

The amount of oxygen at each level is shown in the table below:

Altitude (feet)Altitude (meters)Effective Oxygen %Altitude CategoryExample
0020.9LowBoston, MA
5000152417.3MediumBoulder, CO
6000182916.6MediumMt. Washington, NH
8000243815.4HighAspen, CO
13000396212.7Very High
14000426712.3Very HighPikes Peak
15000457211.8Very High
16000487711.4Very HighMont Blanc
17000518211.0Very High
2000060969.7ExtremeDenali (McKinley)


How Does Oxygen Help At High Altitude?

Physiologically, using supplemental oxygen does the equivalent of reducing the altitude of a climb.

It is calculated that climbing a mountain with oxygen will make the mountain seem 5,000 feet (1,500 meters) lower than it actually is. At rest, the effect is about 15,000 feet (4,500m meters) lower.

So How Do People Climb Mount Everest Without Oxygen?

In short, these climbers are fighting against time to get to the top before their body gives up. With that reduced amount of oxygen in the air, their bodies are slowly dying, and even after making a safe ascent and descent, they risk permanent damages to their brains and bodies.

22% of the 111 deaths that have occurred above 26,000 feet (8,000 meters) at Mount Everest were climbers who did not use supplemental oxygen.

Just because you can do it, doesn’t always mean you should.

Related Questions

How many people climbed Mount Everest without supplemental oxygen? Out of the 4,000 people who have climbed Mount Evert, less than 200 people have done so without oxygen. Most climbers, including Sherpa guides use oxygen above 26,000 feet.

What mountaineering records have been set by people climbing without supplemental oxygen? In 1986, Reinhold Messner became the first person to scale all 8,000 meters (26,000 feet)  peaks without supplemental oxygen. In 2011, Gerlinde Kaltenbrunner became the first woman to summit all 8,000 meters (26,000 feet) peaks without using supplementary oxygen.

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