High Altitude and Your Body: How to Trek Safe and Prevent AMS

Let’s be real: Altitude doesn’t care if you’re fit, experienced, or just super excited to hit that summit. You can be on your first trek or your tenth, but if you climb too high too fast, altitude sickness (aka AMS) can sneak up on you—and ruin your plans.

It doesn’t just happen on Everest. It can hit you at 2,500 - 3,000 meters on a casual Himalayan hike or even while road-tripping to Spiti or Ladakh.

So, how do you prepare? This guide explains what’s happening inside your body when you head up, what altitude sickness actually feels like, and - most importantly - how to avoid it.

🧬 What Happens to Your Body at High Altitude?

As you gain altitude, the air pressure drops. That means every breath you take contains less oxygen than it does at sea level.

So your body starts making some changes:

• You breathe faster to try and grab more oxygen

• Your heart beats quicker to send that oxygen where it’s needed

• You might feel more tired—even when you’re just walking on flat ground

• Over a few days, your body begins producing more red blood cells to carry oxygen better (but this takes time)

That process of adjusting? It’s called acclimatization.And it’s your best defense against altitude sickness.

But if you climb too high too fast? That’s when problems begin.

⚠️ Altitude Sickness: What It Is, What It Feels Like

Let’s break it down simply.

Altitude sickness comes in three forms. They’re all connected - and they get more serious the higher you go.

⛑️ 1. Acute Mountain Sickness (AMS)

This is the most common type. And if you’ve felt a bad headache in the hills? You might’ve had mild AMS.

When it shows up:

Usually within 6-24 hours of arriving above 2,500 m

What it feels like:

• Headache (that doesn’t go away with water or rest)

• Nausea and loss of appetite

• Dizziness or fogginess

• Feeling super tired - even if you just sat all day

• Poor sleep (waking up short of breath is common)

What to do:

• Don’t go higher. Seriously. Stop and rest where you are.

• Hydrate, eat well, and take it easy.

• If prescribed by a doctor, you can take Acetazolamide (Diamox) to help acclimatize faster.

• If your symptoms improve after 24-48 hours, you can think about moving up.

• If they get worse? Time to head down - at least 500 to 1,000 m.

🫁 2. High-Altitude Pulmonary Edema (HAPE)

This one’s dangerous. It means fluid is building up in your lungs.

When it shows up:

Usually 2–5 days into a trek above 2,500-3,000 m, especially if you’ve ascended quickly.

What it feels like:

• You’re gasping for breath - even when resting

• You have a cough (sometimes wet or pink-frothy)

• Your chest feels tight

• Your lips or fingertips look blue (sign of low oxygen)

• Walking even 10 steps feels like a struggle

What to do:

• Immediate descent is critical.

• Administer oxygen if you have it.

• This is not a wait-and-watch situation. Get help, go down, or get evacuated.

🧠 3. High-Altitude Cerebral Edema (HACE)

This is the most serious form. It’s when your brain starts swelling due to lack of oxygen.

When it shows up:

Can develop quickly - often as AMS gets worse.

What it feels like:

• You’re confused, disoriented, or acting oddly

• You lose balance or can’t walk straight

• Slurred speech or blank stares

• Hallucinations in extreme cases

What to do:

• Descend immediately - by at least 1,000 m

• Administer oxygen and, if prescribed, Dexamethasone

• This is an emergency. Don’t try to “sleep it off.” Get help now.

🚨 AMS is not something to "push through". Every year, trekkers suffer or are evacuated because they ignored symptoms. Listen to your body.

🧗 Who Is at Risk?

Altitude sickness can affect anyone, regardless of age, fitness level, or experience. However, certain factors increase susceptibility:

• Rapid Ascent: Ascending quickly without allowing time for acclimatization.

• Previous Altitude Illness: History of AMS, HAPE, or HACE.

• Physical Exertion: Strenuous activity shortly after arrival at high altitude.

• Dehydration and Poor Nutrition: Inadequate fluid and calorie intake.

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It's important to note that even seasoned trekkers can experience altitude sickness if proper precautions aren't taken.

🛡️ How to Prevent Altitude Sickness (The Right Way)

Altitude sickness is almost always preventable - if you give your body time and follow some smart habits. Here’s how:

🐢 1. Gradual Ascent is Everything

Your body needs time to adjust. Rushing is what causes AMS. Follow these ascent rules when planning a trek:

• Stay below 2,500 m on Day 1.

• After that, gain no more than 300–500 m in sleeping altitude per day.

• For every 1,000 m elevation gain, take 1 full rest day (no further ascent).

• Use the "Climb high, sleep low" rule: Go higher during the day, but come down to sleep lower.

• Treks like Roopkund, Stok Kangri, or even Hampta Pass have steep ascents. Plan acclimatization camps into your itinerary.

💧 2. Stay Hydrated and Well-Fueled

• Drink 3-4 liters of water per day (cold, dry air dehydrates you faster).

• Avoid alcohol and smoking - they worsen dehydration and lower oxygen.

• Eat high-carbohydrate meals (dal-rice > protein-heavy diets at altitude).

• Include salty snacks, soups, and ORS sachets to maintain electrolytes.

😌 3. Don’t Overexert on Day 1

• Go slow. Talk at a comfortable pace.

• Avoid heavy loads or long summit pushes on your first day at high altitude.

• Let your body ease into the new environment.

Overexertion and physical strain at high altitudes can increase the risk of Acute Mountain Sickness (AMS), although they are not direct causes. Excessive physical exertion in this low-oxygen environment can increase oxygen demand, which stresses the body further when oxygen availability is already limited. This can hinder acclimatization. Hence rest is a key part of the acclimatization process.

💊 4. Consider Preventive Medication (Talk to Your Doctor)

• Acetazolamide (Diamox): Helps with acclimatization. May be taken 24 hours before ascent and continued for 2–3 days.

• Dexamethasone: Reserved for emergency use or when Diamox isn’t suitable.

• Only take prescribed medication - don’t self-medicate.

📊 Oxygen Levels at Different Altitudes

Altitude (m)	Approx. Oxygen Availability
Sea Level	100%
2,500 m	~75%
3,000 m	~70%
4,000 m	~60%
5,000 m	~50%
5,500+ m	~45% or lower

🧠 This drop in oxygen is why walking uphill becomes exhausting - and why rest days matter.

🧰 Pre-Trek Checklist for Altitude Safety

• ☑️ Add 1-2 days of acclimatization before your trek starts (like Manali before Hampta Pass)

• ☑️ Build cardio with stair climbs, hikes, and breathing work

• ☑️ Know the signs of AMS, HAPE, and HACE

• ☑️ Pack a basic first aid kit, water bottle, snacks, and warm layers

• ☑️ Have a turn-back plan. The mountain’s not going anywhere.

🧠 Final Takeaway: Respect the Altitude

Altitude doesn't care about your age, strength, or how badly you want the summit. It only respects preparation. The best trekkers are the ones who know when to pause, when to rest, and when to descend.

Take it slow. Listen to your body. The trail will still be there tomorrow.

Satish Gogineni

Satish Gogineni is an Indian-born endurance athlete, adventurer, and landscape photographer who thrives in the world’s harshest terrains. He’s run 14 marathons—including four World Marathon Majors—and climbed some of the planet’s highest peaks, famously summiting Everest and Lhotse within 19 hours. In 2025, he became the first Indian to ski solo and unsupported to the South Pole, a 51-day journey to spotlight mental health and suicide prevention in India.