Quick answer: altitude illness can start once you sleep above about 8,200 feet (2,500 meters), and the most common form, acute mountain sickness, feels like a bad hangover with a headache, nausea, tiredness and poor sleep. The CDC advises against going straight from low elevation to a sleeping elevation above 9,000 feet in one day, and above 10,000 feet raising your sleeping elevation by no more than about 1,600 feet a day. Stop going higher if you have symptoms, and descend right away if someone becomes confused, cannot walk straight or is breathless at rest.
Mountain campgrounds have a lot going for them: cool summer nights, wildflower meadows and huge views. They also sit at elevations where the air holds less oxygen than most bodies are used to. Visitors who fly in from the coast on Friday and pitch a tent at 9,500 feet that evening are often surprised by a pounding headache before dinner.
This guide explains what altitude does to the body, how to plan a trip that gives you time to adjust and the changes elevation brings to cooking, water and weather at camp. It is one part of our broader camping safety guide.
Sources: Centers for Disease Control and Prevention, CDC Yellow Book chapter “High-Altitude Travel and Altitude Illness”; CDC guidance on making water safe in an emergency (boiling at elevations above 6,500 feet); World Health Organization, “Ultraviolet radiation” fact sheet; USDA Food Safety and Inspection Service, “High Altitude Cooking and Food Safety”; National Park Service, Rocky Mountain National Park visitor information. Checked October 2026. General information, not medical advice. Talk to your doctor before high-altitude travel if you have heart or lung disease, are pregnant or have had altitude illness before.
What Happens to Your Body at Altitude
Air at high elevation contains the same percentage of oxygen as air at sea level, but the pressure is lower, so each breath delivers less oxygen to the lungs. The body responds by breathing faster and deeper, raising the heart rate and, over days and weeks, making other adjustments. This process is called acclimatization.
Problems arise when people climb faster than their bodies can adjust. According to the CDC Yellow Book, altitude illness becomes a real possibility above about 2,500 meters (8,200 feet), although sensitive people can feel symptoms lower. The key number is sleeping elevation, not the highest point you hike to during the day.
Fitness does not protect you. Athletes and marathon runners get altitude sickness too, and a person who felt fine on one trip can feel unwell on the next. The best predictor is how you reacted on past trips at similar heights and how fast you ascend.
The Three Forms of Altitude Illness
The CDC describes three related conditions. Knowing the difference helps you decide whether to rest or to head downhill right now.
Acute mountain sickness (AMS)
AMS is the most common form. It usually begins 6 to 12 hours after arriving at a new, higher elevation. The main symptom is a headache, along with one or more of the following:
- Tiredness or weakness
- Loss of appetite, nausea or vomiting
- Dizziness or light-headedness
- Trouble sleeping
Many people compare it to a hangover. Mild AMS usually improves over a day or two if you stop going higher.
High-altitude cerebral edema (HACE)
HACE is a severe progression of AMS involving swelling of the brain. Warning signs include confusion, unusual drowsiness, changes in behavior and loss of coordination, such as stumbling or being unable to walk heel to toe in a straight line. HACE can become life-threatening quickly and requires immediate descent and medical care.
High-altitude pulmonary edema (HAPE)
HAPE is fluid in the lungs. It can happen with or without AMS symptoms. Watch for breathlessness at rest, a cough, chest tightness, unusual fatigue and needing to stop to catch your breath far more than others in the group. Like HACE, HAPE is an emergency that calls for descent and medical help.
| Condition | Key signs | What to do |
|---|---|---|
| AMS | Headache plus nausea, fatigue, dizziness, poor sleep | Stop ascending, rest, descend if worse |
| HACE | Confusion, drowsiness, stumbling, trouble walking a straight line | Descend immediately, get emergency help |
| HAPE | Breathless at rest, cough, chest tightness, extreme fatigue | Descend immediately, get emergency help |
How to Plan a Trip That Lets You Acclimatize
The single most effective prevention tool is a gradual ascent. The CDC Yellow Book suggests:
- Avoid going straight to a high sleeping elevation. Try not to travel from low elevation to a sleeping elevation above 2,750 meters (about 9,000 feet) in a single day.
- Spend a night partway up. A night or two at an intermediate elevation, such as a mountain town below 8,000 feet, gives your body a head start.
- Go up slowly once you are high. Above 3,000 meters (about 9,800 feet), raise your sleeping elevation by no more than 500 meters (about 1,600 feet) per day.
- Build in rest days. Add an extra night at the same elevation every three to four days on longer trips.
- Climb high, sleep low. Hiking to a higher point during the day and returning to a lower camp at night is a classic mountaineering practice.
For a weekend camper, this might simply mean booking a motel or a lower campground for the first night and moving up to the high campground on day two.
Ask a doctor about medication
Prescription medicines such as acetazolamide are used to help prevent altitude illness in people at higher risk or those who must ascend quickly. The CDC recommends talking with a healthcare provider before your trip; this is not something to start without medical advice.
Habits that help
- Take it easy the first day. Light activity is fine; save the big hike for later in the trip.
- Limit alcohol early on. The CDC suggests avoiding heavy drinking for the first 48 hours at altitude.
- Drink enough water. Dehydration does not cause AMS, but its symptoms overlap and make it harder to tell what is going on.
- Eat regular meals, even if your appetite is low.
What to Do if Someone Feels Sick
Treat any illness at altitude as altitude illness until proven otherwise. The CDC’s guidance boils down to three rules:
- Do not go higher with symptoms. Rest at the same elevation until they resolve.
- Descend if symptoms get worse or do not improve after a day of rest.
- Descend immediately for signs of HACE or HAPE, even at night, and seek emergency care. A drop of 300 to 1,000 meters often brings quick improvement.
Never leave a person with symptoms alone in a tent. Confusion can sneak up, and someone who is getting worse may not recognize it. Simple pain relievers can ease a mild headache, but if the headache does not improve or new symptoms appear, plan to descend.
Children at altitude
Children can get altitude illness at the same rates as adults. Young kids may not be able to describe a headache, so watch for fussiness, changes in eating, sleep problems and unusual tiredness. The same rule applies: stop going higher and descend if they get worse.
Who Is More Likely to Get Sick
Anyone can develop altitude illness, but the CDC Yellow Book lists several factors that raise the odds. Knowing them helps you decide how cautious your plan needs to be.
- A past episode. People who had altitude illness before are more likely to get it again at a similar elevation and rate of ascent.
- Living near sea level. Residents of low-lying areas have had no chance to adapt before the trip.
- Fast ascent. Flying or driving to a high campground on the same day is the classic setup for trouble.
- Hard exertion on arrival. A long hike or heavy hauling of gear on the first day adds strain.
- Certain health conditions. Heart and lung problems, including some that are well controlled at home, can behave differently at altitude. A pre-trip conversation with a doctor is worth the time.
Age and fitness, on the other hand, are poor predictors. Fit young adults often push harder on day one, which may explain why they are far from immune.
Sleeping Well at High Camps
Poor sleep is one of the most common complaints at elevation. The CDC Yellow Book describes periodic breathing, a pattern in which breathing speeds up, slows and briefly pauses during sleep. It can wake people with a feeling of breathlessness and can worry tentmates, but on its own it is a normal response to altitude and usually eases as the body adjusts.
A few practical steps make nights more comfortable. Sleep slightly propped up on a stuff sack of clothes, keep the tent vented to cut condensation, and use a sleeping bag rated for the overnight low. Ask your doctor before using any sleep medication at altitude, since some sedatives can slow breathing.
How Elevation Changes Life at Camp
Altitude affects more than your body. Several everyday camp tasks work differently up high.
Stronger sun
The World Health Organization notes that UV levels rise by roughly 10 percent with every 1,000 meters of altitude. Thin, dry mountain air means sunburn can happen fast, even on cool days. Wear a brimmed hat and sunglasses, and reapply sunscreen often.
Colder nights
Temperatures generally fall as you climb, and clear mountain skies let heat escape after sunset. A campground that feels warm at 3 p.m. can drop near freezing overnight in midsummer. Pack layers rated for the low and use our layering system for cool nights as a guide. If you struggle to stay comfortable, our tips on staying warm while camping in cold weather cover sleeping systems and fuel for the body.
Afternoon storms
In many western mountain ranges, summer thunderstorms build in the afternoon. Start hikes early and plan to be off exposed ridges and summits before clouds tower. Lightning is a separate hazard from altitude illness but often shows up on the same trips.
Cooking and boiling water
Water boils at a lower temperature as elevation rises, so foods that cook in boiling water take longer. The USDA Food Safety and Inspection Service notes that cooking times and methods may need adjusting above about 3,000 feet. Bring a little extra fuel for your stove.
For water treatment, the CDC advises boiling water for one minute to make it safe, or for three minutes at elevations above 6,500 feet. Our guide on finding and treating water while camping compares filters, chemicals and boiling.
Driving up
Many visitors reach high campgrounds by car. Rocky Mountain National Park’s Trail Ridge Road, for example, tops out above 12,000 feet, according to the National Park Service. A quick drive up from a low-lying city does not give your body time to adjust, so the CDC’s sleeping-elevation advice still applies even if you never set foot on a trail.
A High-Elevation Camping Checklist
- Check the campground’s elevation before booking, not just the nearest town’s
- Plan a lower first night if the campsite sits above 9,000 feet
- Talk to a doctor about medication if you have had altitude illness before
- Pack warm layers, a warm sleeping bag, sunscreen, sunglasses and a brimmed hat
- Bring extra stove fuel and allow longer cooking times
- Agree as a group that anyone with symptoms will say so early
- Know the route to lower elevation and the nearest medical facility
Frequently Asked Questions
At what elevation does altitude sickness start?
The CDC says altitude illness becomes a concern above about 8,200 feet (2,500 meters), though sensitive people can have symptoms lower. Your sleeping elevation matters more than the highest point you visit during the day.
How long does it take to acclimatize?
Mild symptoms often improve within a day or two of resting at the same elevation. Full adjustment takes longer, which is why the CDC recommends gradual ascent and rest days on extended trips.
Can you get altitude sickness while car camping?
Yes. Driving quickly to a high campground gives your body no time to adjust. The same sleeping-elevation guidance applies whether you hike or drive.
Does drinking more water prevent altitude sickness?
Staying hydrated is sensible, but it does not prevent altitude illness on its own. Gradual ascent is the most effective prevention.
When should you go down the mountain?
Descend if symptoms get worse or do not improve with rest, and descend immediately for confusion, stumbling, breathlessness at rest or a persistent cough.
