At What Height Does Altitude Sickness Start? Key Signs and Prevention Tips

Altitude sickness typically starts at elevations around 6,600 feet (2,000 meters). However, symptoms can become more noticeable and severe above 8,000 feet (2,400 meters), where the risk of acute mountain sickness (AMS) increases. 

Altitude sickness can affect anyone, even seasoned climbers, once you hit specific elevations. But don’t worry—with a little preparation, you can enjoy the heights without the headaches (literally). In this article, we’ll break down the altitudes where symptoms begin, how to recognize them, and tips to prevent altitude sickness.

What is Altitude Sickness? Understanding the Basics

What Causes Altitude Sickness?

Altitude sickness, or mountain sickness, happens when your body struggles to adjust to lower oxygen levels as you ascend. As you climb higher, the air gets thinner, making it harder for your body to absorb enough oxygen. This is where hypoxia comes in—the sneaky culprit behind those altitude-related symptoms. Essentially, your body is trying to function with less oxygen, and that’s when the trouble begins.

How Common is Altitude Sickness?

Altitude sickness isn’t rare. In fact, it’s something a significant number of people experience, even at elevations as low as 6,600 feet. For some, it’s just mild discomfort—an annoying headache or a bit of dizziness—while others might face more serious issues like nausea and fatigue. But don’t worry, most of the time, with the right preparation, it’s manageable. Knowing how your body reacts at different elevations is crucial to keeping those symptoms at bay.

At What Altitude Does Sickness Start? Key Elevation Thresholds

Altitude Sickness Symptoms by Height

Height Range	Symptoms
6,600 – 8,000 feet (2,000 – 2,400 meters)	Headache, slight dizziness, mild nausea
8,000 – 12,000 feet (2,400 – 3,600 meters)	Acute Mountain Sickness (AMS): headaches, fatigue, difficulty sleeping, shortness of breath
12,000+ feet (3,600+ meters)	Severe symptoms: High-altitude pulmonary edema (HAPE), high-altitude cerebral edema (HACE), confusion, severe breathlessness, risk of death

Initial Symptoms at Lower Altitudes (6,600 to 8,000 feet)

Altitude sickness can start as low as 6,600 feet—right around where many ski resorts and popular hiking trails are. You might feel a slight headache, some dizziness, or even a bit nauseous. Not exactly the welcome party you were hoping for, but these early signs are your body’s way of saying, “Hey, slow down!” It’s important to pay attention to these initial symptoms because ignoring them can lead to more severe issues as you continue to ascend.

High Altitudes (8,000 to 12,000 feet)

Once you hit 8,000 feet, things can get a little more serious. This is where acute mountain sickness (AMS) can rear its head. Symptoms include stronger headaches, loss of appetite, difficulty sleeping, and general fatigue. It’s your body asking for a breather—literally. At this elevation, it’s crucial to take things slow, allow for acclimatization, and listen to what your body needs. Rest, hydration, and pacing yourself are key strategies for preventing AMS from worsening.

Extreme Altitudes (12,000+ feet)

At elevations above 12,000 feet, the risk of severe altitude sickness increases significantly. You might hear about HAPE (high-altitude pulmonary edema) and HACE (high-altitude cerebral edema), both of which are serious conditions requiring immediate attention. Symptoms like confusion, severe breathlessness, or an inability to walk straight are major red flags. Supplemental oxygen and immediate descent are crucial at this point. If you’re venturing into these extreme altitudes, you need to be well-prepared and knowledgeable about these potential dangers.

Recognizing the Symptoms of Altitude Sickness

Mild Symptoms: When to Take Action

Mild altitude sickness symptoms are your body’s early warning signs. Symptoms look similar to the symptoms of hypothermia. Look out for things like headaches, fatigue, dizziness, and a reduced appetite might not seem like a big deal, but if ignored, they can get worse. The key is to listen to your body and not push it. Resting when these symptoms appear can prevent them from escalating. Remember, the best thing you can do is give your body time to adjust before continuing your ascent.

Severe Symptoms: When to Seek Immediate Help

Severe symptoms of altitude sickness include shortness of breath, confusion, chest tightness, and difficulty walking. These can indicate HACE or HAPE, both of which require immediate medical attention. If your breathing gets labored, or if you experience confusion or an inability to stay balanced, it’s time to descend—no questions asked. These symptoms mean your body is in distress, and delaying treatment can be life-threatening.

Risk Factors: Who is Most Likely to Get Altitude Sickness?

Who is More Susceptible?

Anyone can get altitude sickness, but those who live at lower elevations are at higher risk. People coming straight from sea level might feel the effects faster than those who are used to living at altitude. Age, fitness level, and even your overall health can also play a role. Interestingly, being young and fit doesn’t necessarily make you immune—sometimes people who are more accustomed to pushing themselves physically may ignore symptoms, putting themselves at greater risk.

Does Acclimatization Reduce Risk?

Yes, and it’s one of the most effective ways to prevent altitude sickness. By gradually ascending and giving your body time to adjust, you lower your chances of getting sick. A good rule of thumb: gain no more than 1,000 to 1,500 feet per day above 8,000 feet, and take a rest day for every 3,000 feet gained. Spending an extra night at intermediate altitudes gives your body the time it needs to acclimatize.

How to Prevent Altitude Sickness

Acclimatization Techniques

Taking your time to climb is the best way to acclimatize. Rest days are essential, and if possible, sleep at lower elevations to help your body recover overnight. This gradual approach helps your body adapt without stressing it too much. “Climb high, sleep low” is a tried-and-true method to help reduce the risk of altitude sickness. If you’re trekking, consider planning your route to include several acclimatization days.

Medications and Oxygen Use

Preventive medications like acetazolamide can help reduce the risk of altitude sickness. This medication works by helping your body adjust more quickly to high altitudes. It’s especially useful if you’re short on time and can’t afford a slower ascent. For those climbing to extreme heights, supplemental oxygen might be necessary to stay safe. It’s also worth carrying a pulse oximeter to monitor your oxygen levels and catch any early signs of trouble.

Hydration and Diet Tips

Staying hydrated is key when you’re at high altitudes. Dehydration can make symptoms worse, so drink plenty of water. Avoid alcohol and caffeine, as they can contribute to dehydration. And if you’re hungry, carbs are your friend—they help your body adjust to the altitude more effectively. Eating small, frequent meals high in carbohydrates can provide the energy needed for acclimatization. Soups are particularly good since they help with hydration as well as nutrition.

Treatment Options: What to Do if You Get Altitude Sickness

Immediate Steps to Take

If you start feeling the symptoms of altitude sickness, the best move is to stop ascending. Rest, hydrate, and see if the symptoms improve. If they don’t, descending is the safest option. Even a descent of just a few hundred feet can make a big difference in how you feel. If symptoms are mild, resting for 24 to 48 hours can sometimes be enough for your body to adapt.

When Medication is Necessary

For moderate cases, medications like acetazolamide can help relieve symptoms. Another option is dexamethasone, which can reduce brain swelling associated with HACE. These medications should be taken under medical supervision. But if things get serious, immediate descent and possibly medical attention will be necessary. Always err on the side of caution—altitude sickness can escalate quickly.

Advanced Treatments for Severe Cases

For severe altitude sickness, hyperbaric therapy or oxygen treatments can help, but these are usually only needed in extreme cases. A portable hyperbaric chamber can simulate lower altitudes and provide temporary relief until descent is possible. Supplemental oxygen is also a key treatment for HAPE, helping to relieve symptoms and stabilize the individual until they can get to a lower elevation. Prevention, as always, is the best medicine—so plan your ascent carefully.

The Science Behind Altitude Sickness

How the Body Responds to High Altitudes

At high altitudes, the body undergoes several changes to adapt to lower oxygen levels. Your breathing rate increases, your heart beats faster, and over time, your body produces more red blood cells to carry oxygen more efficiently. These physiological responses are all part of the acclimatization process, but they also put extra stress on the body. Understanding these changes can help you recognize why acclimatization is so important and why pushing too hard can be dangerous.

The Role of Hypoxia

Hypoxia, or oxygen deprivation, is the underlying cause of most altitude sickness symptoms. As you ascend, the lower atmospheric pressure means there is less oxygen available. This triggers the body to compensate in various ways, but if it cannot keep up, symptoms begin to appear. Recognizing hypoxia early is key to preventing more serious conditions like HACE or HAPE, where fluid accumulates in the brain or lungs due to inadequate oxygen levels.

Key Takeaways: At What Height Does Altitude Sickness Start?

1. Altitude sickness can start at 6,600 feet – Symptoms can begin at relatively moderate elevations, such as popular hiking spots or ski resorts.
2. Initial symptoms include headaches and dizziness – Early signs are mild but shouldn’t be ignored, as they can worsen with continued ascent.
3. Serious conditions like HAPE and HACE occur above 12,000 feet – These severe forms of altitude sickness require immediate medical attention and descending to lower altitudes.
4. Anyone can get altitude sickness – Living at lower elevations or being physically fit doesn’t necessarily protect you from altitude sickness.
5. Acclimatization is crucial – Slowly ascending, taking rest days, and staying hydrated help your body adjust and reduce the risk of altitude sickness.
6. Medications can help prevent symptoms – Acetazolamide and supplemental oxygen are useful tools to mitigate altitude sickness, especially for quick ascents.
7. Descent is the best remedy for severe symptoms – If symptoms worsen, descending even a few hundred feet can significantly improve your condition.