What Happens to Your Body at High Altitudes

What Happens to Your Body at High Altitudes

Category Acute Mountain Sickness Altitude And Health

By Swathi Chatrapathy


Let’s talk about what happens to your body at high altitudes.

Trekking in the Himalayas implies that you will be trekking at high altitudes and it’s important for you to know about the effects of high altitudes on the human body.

This article is mandatory reading for any trekker aiming to attempt any of our high altitude treks, especially if you plan to climb any of the 15-16,000-ers like Rupin Pass, Buran Ghati, Bali Pass, Kedartal Trek, Khopra Ridge and Everest Base Camp via Gokyo Ri.

First, let’s talk about what happens to the air at high altitude

You must know that anything above 8,000 ft from sea level is high altitude.

At this high altitude, the air pressure drops and there’s lesser oxygen available in the air.

Let me explain.

At a lower altitude, say, at sea level, there’s a certain amount of pressure in the air. At this pressure, air particles are pressed together, making the oxygen content in the air more concentrated. So one deep breath of air at sea level will give you a lot of oxygen.

However, as you climb higher, this pressure decreases. Air particles get scattered about. Consequently, even the oxygen in the air gets scattered. So the same deep breath of air at high altitude gives you lesser oxygen content.

This is what people often call “thin air” or “rarified air”.

It’s not lesser oxygen. It’s just a lesser concentration of oxygen because of the lower pressure.

To give you an idea, the air pressure at sea level is 101.3 kPa (kilopascal). However, as you climb to around 16,000 ft (the altitude of Roopkund), the pressure drops dramatically to 54.8 kPa. Higher up, at around 29,028 ft (the altitude of Everest), it further drops to 30.8 kPa.

That’s less than one-third of the air pressure at sea level!

Altitude classification, oxygen concentration

Oxygen concentration at different altitudes

That’s why you cannot suddenly climb from sea level to 29,500 ft in a day.  That would be like stepping out of an airplane mid-air. (Most commercial planes fly at this altitude.) Your body will not cope with it.

It takes days for your body to adjust at high altitudes which is why most of our high altitude treks are around 8 days long with rest days in between.

This action of “coping up” by your body is called acclimatisation.

What happens to your body at high altitudes?

Well, your body is used to a certain amount of oxygen at sea level.

When it suddenly gets lesser oxygen, it naturally tries to compensate by trying to take in more oxygen.

So your breathing becomes faster.

Next, your body recognises that there is lesser oxygen in your blood — so it compensates by increasing the quantity of oxygenated blood.

This means your heart starts pumping faster. Your pulse rate increases.

Third, your bone marrow, which is responsible for managing your blood count, starts producing more red blood cells. Red blood cells are the vehicles that carry around blood in your body.

But having too many red blood cells is not good for you. They can cause a sort of traffic jam in your body.

Think of the consistency of ketchup. That’s how your blood could become. It could also clot. Especially during times of inactivity.

Simply put, your blood becomes thicker.

oxymeter, reading, oxygen level

Now, since both, your lungs and heart, are working harder than usual, your body tries getting rid of any excess baggage that it might be housing. It does this by getting rid of excess fluids — what it perceives as useless bodyweight.

This makes you urinate more often.

The scientific term for this is diuresis. A book I was reading by Stephen Bezruchka on this subject said you can lose nearly 2% of your body weight in water!

So at high altitude, it’s normal to wake up in the night to pee. If you’ve gone on a trek, it would explain all those midnight nature’s calls.

Another thing that may happen to your body is that you sleep less.

Often, your body forgets to breathe deep in your sleep. And your brain suddenly wakes you up to remind you to breathe! So if you don’t sleep too well at high altitude, it’s normal. Remember, it’s just the changes going through the body at high altitudes and a way for your body to acclimatise.

What you need to know about these changes in your body

The thing you need to know about all these changes in your body is that your body goes through these changes occur even while you’re resting.

This has nothing to do with trekking or mountaineering or any exercise.

Even if you’re simply lying down at high altitude, your body is spending a lot of energy, because it’s in overdrive.

Note that everything I have mentioned till now is about your body’s natural reaction to altitude gain. They aren’t abnormal changes. They are not “symptoms” of anything.

Almost everyone’s body at high altitudes adjust. But sometimes, our body might respond more slowly, or may not respond at all.

Most of our bodies go through these changes and adjust well to altitude. But sometimes, our body might respond more slowly, or may not respond at all.

That’s when we get altitude sickness, otherwise known as High Altitude Sickness.

If we understand the science behind it, it is not difficult to treat altitude sickness.

The biggest problem trekkers face is lack of knowledge. Which is why I am writing this article.


I want you to start learning these things if you’re a high altitude trekker. If you already know these things, share your knowledge with others. The more you learn, the less dependent your life will be on others. For all you know, you could save someone else’s life!

In my following articles, I’ll dive deeper into how to prevent and treat altitude sickness.

For now, I highly recommend going through this page on our website to learn about anything altitude-related.

I hope you found this article helpful. Don’t hesitate to ask me if you have any questions. Also, if you think I’ve missed something out feel free to mention it in the comments section below.

Swathi Chatrapathy

Chief Editor

About the author

Swathi Chatrapathy heads the digital content team at Indiahikes. She is also the face behind India's popular trekking video channel, Trek With Swathi. Unknown to many, Swathi also writes a weekly column at Indiahikes which has more than 100,000 followers.

A TEDx speaker and a frequent guest at other events, Swathi is a much sought after resource for her expertise in digital content.

Before joining Indiahikes, Swathi worked as a reporter and sub-editor at a daily newspaper. She holds a Masters's in Digital Journalism and continues to contribute to publications. Trekking, to her, is a sport that liberates the mind more than anything else. Through trekking, Swathi hopes to bring about a profound impact on a person's mind, body and spirit.

Related Videos

3 Life Saving Drugs (LSD) To Tackle Altitude Sickness

5 Signs You May NOT Recognise As Acute Mountain Sickness (AMS)

What is Acute Mountain Sickness (AMS)?

What are HAPE and HACE?

What is HACE (High Altitude Cerebral Edema) and how do you treat it?