Understanding Altitude and How It Affects Your Body

As you gain elevation, atmospheric pressure decreases, meaning each breath you take contains fewer oxygen molecules. Your body compensates by breathing faster and increasing heart rate — but these adjustments take time. When you ascend too quickly, or go too high without adequate acclimatization, the result can be altitude sickness, medically known as Acute Mountain Sickness (AMS).

AMS can affect anyone, regardless of age or fitness level. In fact, strong, fit individuals sometimes ascend faster and are at higher risk because they push hard and ignore early warning signs. No one is immune.

The Three Forms of Altitude Illness

1. Acute Mountain Sickness (AMS) — Mild to Moderate

The most common form. Symptoms typically appear 6–12 hours after rapid ascent above 8,000 feet (2,400m) and include:

  • Headache (the defining symptom — if you have a headache at altitude, assume AMS)
  • Fatigue and weakness
  • Loss of appetite, nausea, or vomiting
  • Dizziness or lightheadedness
  • Difficulty sleeping

Mild AMS is unpleasant but manageable with rest, hydration, and no further ascent. However, it can rapidly progress to more dangerous conditions if ignored.

2. High Altitude Pulmonary Edema (HAPE) — Life-Threatening

Fluid accumulates in the lungs, severely impairing breathing. HAPE is one of the most common causes of altitude-related death. Symptoms include persistent dry cough, extreme fatigue, shortness of breath even at rest, and bluish skin or lips (cyanosis). HAPE is a medical emergency requiring immediate descent.

3. High Altitude Cerebral Edema (HACE) — Life-Threatening

Fluid accumulates around the brain. Signs include severe headache that doesn't respond to ibuprofen, loss of coordination (ataxia — the "walk the line" test), altered mental status, confusion, and eventually unconsciousness. HACE is a medical emergency. Descend immediately, even at night.

Prevention: The Golden Rules

Ascend Slowly

The most effective prevention is gradual ascent. The general guideline above 8,000 feet (2,400m):

  • Increase your sleeping elevation by no more than 1,000–1,500 feet (300–500m) per night.
  • Follow the maxim: "Climb high, sleep low." Day hikes to higher elevation, returning to a lower camp to sleep, accelerate acclimatization.
  • Build in rest days every 3 days of ascent.

Hydrate Well

Dehydration worsens AMS symptoms. At altitude, you lose water faster through increased respiration. Aim to drink enough to keep your urine pale yellow — this often means consuming significantly more water than at sea level.

Avoid Alcohol and Sedatives

Both alcohol and sleeping pills suppress breathing, which reduces oxygen saturation during sleep — exactly when your body should be recovering and acclimatizing. Avoid them during your first days at high altitude.

Consider Acetazolamide (Diamox)

Acetazolamide is a prescription medication that helps your body acclimatize faster by stimulating deeper breathing. It's commonly used for high-altitude trekking (Kilimanjaro, Everest Base Camp, etc.). Consult a physician before your trip if you're planning to reach elevations above 10,000 feet (3,000m). It is not appropriate for everyone and has its own side effects.

Recognizing AMS in Your Group

One of the dangers of altitude sickness is that the affected person's judgment becomes impaired — they may deny symptoms or insist they're fine. Use the Lake Louise Score as a simple field assessment: if someone at altitude has a headache plus any one of (fatigue, GI symptoms, dizziness, or poor sleep), they have AMS and should not ascend further.

The single most important question to ask is: "Do you have a headache?"

Treatment and When to Descend

Condition Action
Mild AMS Stop ascending, rest, hydrate, take ibuprofen or acetaminophen for headache
Moderate AMS (not improving in 24 hrs) Descend 1,000–3,000 ft immediately
HAPE or HACE Descend immediately, administer supplemental oxygen if available, seek emergency medical care

The Bottom Line

The mountains will always be there. No summit, no schedule, and no ego is worth your life. If you or a companion show signs of serious altitude illness, descend. Do not wait for morning. Do not wait for improvement. Descent is the only reliable cure, and it works remarkably quickly — most HAPE and HACE symptoms improve significantly with even a few hundred meters of altitude loss.

Prepare well, ascend gradually, listen to your body, and the mountains will reward you with experiences worth every careful step.