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Are you planning a big hike, ski, or travel expedition to a location above 8,000 feet sea level? Be alert to the signs of altitude sickness.

Altitude sickness occurs if your body hasn’t adjusted to low oxygen levels in the air.

Whether you’re a seasoned mountaineer or a first-time hiker, understanding altitude sickness is crucial for your safety and well-being.

Learn more about altitude sickness prevention, symptoms, and treatment options.

What Is Altitude Sickness?

Altitude sickness, also known as acute mountain sickness, occurs when the body struggles to adapt to the reduced oxygen levels at higher altitudes.

As you ascend, the atmosphere becomes thinner, which means you get less oxygen with each breath. You may develop altitude sickness when your body doesn’t have enough time to adjust to this change. The good news is that altitude sickness is typically preventable and treatable.

Types of Altitude Sickness

There are several forms of altitude sickness, each with different symptoms and severities.

• Acute Mountain Sickness (AMS) — The most common form of altitude sickness, AMS typically occurs at elevations above 8,000 feet. Symptoms include headaches, nausea, fatigue, and dizziness.
• High-Altitude Pulmonary Edema (HAPE) — A more severe condition affecting the lungs, HAPE results from fluid buildup and requires immediate medical attention.
• High-Altitude Cerebral Edema (HACE) — The most critical form, HACE, involves brain swelling and can be life-threatening.

Symptoms of Altitude Sickness

Altitude sickness typically appears within the first day of reaching high altitudes. It can cause a variety of symptoms.

Recognizing the early signs allows you to adjust your ascent and prevent complications.

Here are the symptoms of altitude sickness:

• Dizziness or lightheadedness — Feeling off-balance.
• Fatigue — Even when resting, you may feel exhausted.
• Headaches — Persistent headaches are often the first sign.
• Loss of appetite — A reduced desire to eat.
• Malaise — A general sense of feeling unwell.
• Nausea and vomiting — Feeling queasy or nauseous.
• Trouble sleeping — Insomnia or restless sleep.
• Vision changes — Rare but serious, floaters, blurring, or vision loss can indicate severe AMS due to retinal blood vessel ruptures.

Why Does Altitude Sickness Happen?

When you ascend rapidly to higher altitudes, the air becomes thinner, and your body needs time to adjust to the change in pressure. If not managed, it can lead to complications like fluid in the lungs or brain swelling.

The more quickly you climb to a high altitude, the higher your risk of developing altitude sickness.

Complete acclimatization to high elevation may take weeks to months. However, the acute process, which occurs within the first 3 to 5 days after ascent, is most vital, according to the Centers for Disease Control and Prevention (CDC).

Risk factors for altitude sickness

Ascending slowly and giving your body time to adjust to lower oxygen levels is critical to reducing your risk of altitude sickness.

These risk factors can increase your chances of developing altitude sickness:

• Alcohol and drug use — Drinking alcohol or using certain medications can significantly increase your risk of altitude sickness.
• Higher altitudes — The higher you go, the higher your risk of altitude sickness.
• History of altitude sickness — A history of altitude sickness, particularly severe forms like HAPE or HACE, increases your future risk.
• Speed of ascent — Rapidly reaching higher altitudes raises the likelihood of altitude sickness. Flying to high altitudes rather than walking, hiking, or driving significantly increases this risk. Above 8,000 feet, aim for an ascent of no more than 1,640 feet per day.

Your physical health is not a direct risk factor for developing altitude sickness. However, high altitudes can worsen the symptoms of health issues like anemia and chronic obstructive pulmonary disease.

How common is altitude sickness?

Altitude sickness is rare below 8,000 feet above sea level, but nearly everyone ascending rapidly to 11,000 feet will experience it. Its effects are strongest in people not accustomed to breathing at elevated altitudes.

Susceptibility and resistance to altitude sickness are, in part, genetically determined traits, according to the CDC.

Tips to Prevent Altitude Sickness

Whether trekking in the mountains or flying to a higher elevation, taking steps to prevent altitude sickness will allow you to enjoy a smoother journey.

Try these tips to avoid altitude sickness:

• Carbohydrates — Fuel your body with sugars and starches to reduce your risk of altitude sickness.
• Consult a doctor — Ask them if they suggest taking Acetazolamide (Diamox) before your trip.
• Daytime climbing — Climb higher during the day and descend to lower altitudes for sleep.
• Gradual ascent — Climb slowly to allow your body time to acclimate. Avoid rapid altitude gains.
• Stay hydrated — Drink plenty of water to prevent dehydration.

The best foods for altitude sickness

Try these foods to soothe altitude sickness symptoms:

• Complex carbs — Oats, sweet potatoes, peas, beans, and brown rice offer a gradual and sustained energy release. Sustained energy can be beneficial when adapting to lower oxygen levels.
• Foods rich in potassium — Try avocados, bananas, broccoli, cantaloupe, celery, granola, greens, potatoes, and tomatoes to increase your potassium intake. Potassium helps maintain proper muscle and nerve function.
• Iron-rich foods — Iron is necessary to transport oxygen throughout the body. Oxygenation can help you acclimate to new altitudes. Eat iron-rich foods, like meat, poultry, seafood, and legumes, to help your blood hold more oxygen.
• Water — Staying hydrated is essential.

Avoid caffeine and alcohol, at least initially. Try to limit your salt intake as well. Both of these can dehydrate you, making altitude sickness worse.

How Do You Treat Altitude Sickness?

If symptoms occur, try these options to soothe symptoms:

• Descend — If you experience mild symptoms, descend to a lower altitude.
• Medications — Try seeking medical attention. If you’re struggling with pain, an over-the-counter pain reliever may help.
• Oxygen therapy — If your oxygen levels are low, oxygen therapy can help you feel better by increasing oxygen levels in your blood.

How long does altitude sickness last?

For most healthy individuals, mild symptoms of altitude sickness will improve within 24 to 48 hours as the body gets used to the change in air pressure.

Severe cases may persist or worsen over time. If this is the case, seek medical care. You may need to descend to lower altitudes for relief.

How Serious Is Altitude Sickness?

The milder altitude sickness, AMS, isn’t necessarily dangerous as long as you stop ascending. Though AMS is unpleasant and may disrupt your trip, it resolves within a few days.

The more severe forms of altitude sickness, HAPE and HACE, are potentially life-threatening. If you experience symptoms of HAPE or HACE, you should immediately stop ascending and receive medical care.

What are the complications of altitude sickness?

Altitude sickness can have serious consequences if it progresses to HAPE or HACE. HAPE can become life-threatening within 12 hours, while HACE can be fatal within 24 hours.

Take note of the early signs of altitude sickness. If you start feeling them, stop your ascent to help prevent severe complications.

When Should I Go to the Emergency Department?

You should seek emergency medical care if you experience severe symptoms of altitude sickness.

These symptoms are signs you should seek medical care immediately:

• Chest tightness or pain.
• Clumsiness or coordination problems.
• Confusion.
• Decreased consciousness.
• Shortness of breath, even when resting.
• Slurred speech.

These are all signs of severe forms of altitude sickness: HAPE and HACE. These conditions can be deadly within hours, so it is essential to seek medical attention immediately.