Altitude sickness: symptoms, what happens to your oxygen and heart rate, and how to prevent it

Short answer

Altitude sickness is the headache, nausea, tiredness and dizziness that can start 2–12 hours after going too high too fast, usually above about 8,000 feet (2,450 m). If you have a headache plus one other symptom that eases within 12–48 hours at the same height, it is usually mild acute mountain sickness; if you become confused, unsteady or breathless at rest, descend and get emergency help.

Feeling flattened on your first day in Breckenridge or Cusco is not weakness, and it is not a sign you are out of shape: the CDC states that training and physical fitness do not change the risk. Before you blame yourself, check what your body already recorded — a faster resting heart rate, a lower oxygen reading and a broken first night are what thinner air does to everyone.

Note: this article explains a common travel condition and is not medical advice. It cannot diagnose your symptoms. Confusion, loss of balance, or breathlessness at rest at altitude are emergencies: descend and get help.

When altitude sickness is an emergency: HACE and HAPE

Most altitude sickness is miserable but harmless and settles on its own. Two forms are dangerous, and it is worth knowing them before anything else.

High-altitude cerebral edema (HACE) is swelling of the brain. The CDC Yellow Book calls it "end-stage" acute mountain sickness, describes it as altered mental status, ataxia (loss of coordination and balance), confusion and drowsiness, and warns that coma can follow within 24 hours of onset (CDC Yellow Book).

High-altitude pulmonary edema (HAPE) is fluid in the lungs. According to the same chapter, it starts with chest congestion, a cough, breathlessness that is out of proportion to the effort, and a drop in how much you can do. It then progresses to breathlessness at rest and frank respiratory distress, often with bloody sputum, typically over 1–2 days. HAPE is rare at ski-resort heights — roughly 1 per 10,000 skiers in Colorado — and becomes more common higher up, at up to 1 per 100 travelers above 4,300 m (14,000 ft).

Get help and go down immediately if you or someone with you has any of these at altitude:

• confusion, odd behavior, or being hard to wake;

• stumbling, or being unable to walk heel to toe in a straight line;

• breathlessness while resting, or a cough that keeps getting worse;

• pink or bloody sputum;

• symptoms that keep getting worse even though you are resting and not going higher.

In the US, call 911; on a trek or abroad, call local rescue or emergency services. For HAPE, the CDC says descent is "urgent and mandatory". The Wilderness Medical Society guideline strongly recommends descent for HACE and HAPE, with supplemental oxygen while waiting to go down or when descent is not possible (doi.org). Never leave someone with these signs alone, and never let them go down by themselves.

What is altitude sickness?

Altitude sickness is the umbrella term for the illnesses that happen when your body has not yet adjusted to lower oxygen pressure at height. The air at altitude still contains about 21% oxygen, but the pressure is lower, so each breath delivers less. At around 10,000 feet (3,050 m), the oxygen pressure you breathe in is only 69% of the sea-level value, and acute exposure can lower arterial oxygen saturation to 88–91% (CDC Yellow Book).

Doctors separate three conditions:

• Acute mountain sickness (AMS) — the common one. Headache plus nausea or poor appetite, fatigue, or dizziness.

• HACE — brain swelling, which the CDC describes as "end-stage" AMS.

• HAPE — fluid in the lungs, which the CDC notes can occur on its own or together with AMS and HACE.

The body can adapt. The CDC notes that people can adjust to moderate hypoxia at altitudes up to about 5,200 m (17,000 ft) given time. That adjustment is called acclimatization, and almost every prevention rule below is about giving it enough time.

What are the 3 stages of altitude sickness?

There is no official "3 stages" of altitude sickness. People who search for it usually mean one of two things. The first is the three conditions above — AMS, HACE and HAPE. The second is severity. Researchers use the 2018 Lake Louise AMS score, which rates four symptoms from 0 to 3: headache, gut symptoms, fatigue or weakness, and dizziness or light-headedness. AMS is defined as a total of 3 or more points, including at least 1 point for headache, after a recent gain in altitude. For researchers who want to grade it, the consensus suggests 3–5 points for mild, 6–9 for moderate and 10–12 for severe (doi.org).

One detail matters for anyone with a sleep tracker: the 2018 revision removed disturbed sleep from the score, because poor sleep at altitude turned out to be caused by low oxygen itself and is not closely related to AMS. A bad first night is expected. It is not, on its own, a diagnosis.

Altitude sickness symptoms: what it feels like

Headache is the cardinal symptom. The CDC describes it as usually accompanied by at least one of: loss of appetite, dizziness, fatigue or nausea, and says AMS symptoms are like those of an alcohol hangover (CDC Yellow Book). The four items of the Lake Louise score put the same list into plain terms (doi.org):

• headache, from mild to incapacitating;

• gut symptoms: poor appetite, nausea, at worst vomiting;

• fatigue or weakness out of proportion to what you did;

• dizziness or light-headedness.

What does altitude sickness feel like?

Mild altitude sickness usually feels like a bad hangover or the start of a flu, without the fever. Your head aches, food is unappealing, the stairs to your hotel room leave you breathless, and you want to lie down. Being short of breath when you climb a slope is normal at altitude for everyone; being short of breath while sitting still is not, and points towards HAPE. A useful check is behavior: in mild AMS a person is uncomfortable but clear-headed. If someone becomes confused, unusually sleepy or clumsy, think HACE rather than "just tired".

How soon does altitude sickness start, and how long does it last?

According to the CDC, symptoms usually begin 2–12 hours after arrival, and AMS generally resolves within 12–48 hours if you do not go higher (CDC Yellow Book). In a survey of 3,158 adult visitors to Colorado resorts at 6,300–9,700 feet, 65% of those who developed AMS had symptoms within the first 12 hours (doi.org). A headache that appears for the first time on day 5 at the same altitude, without any further climb, fits AMS less well, and other causes are worth considering (see "Is it altitude sickness, or something else?" below).

Who gets altitude sickness?

Anyone can. In the Colorado survey, 25% of visitors developed AMS. The odds were 3.5 times higher for people living below 3,000 feet, 2.8 times higher for people who had had AMS before, and about twice as high in visitors younger than 60 (doi.org). The CDC notes that people over 50 have slightly less risk, that children are as susceptible as adults, and that your past response to altitude is the most reliable guide — but only at a similar altitude and ascent rate.

Fitness is not a shield. The CDC says training and physical fitness do not affect the risk of altitude illness. The Colorado survey did find more AMS among people who described themselves as in poor or average shape, but a marathon runner who flies straight to 11,000 feet can still be laid flat. Feeling fit can also make it tempting to push hard on day one, which works against acclimatization.

At what altitude does altitude sickness start?

Risk depends mostly on where you sleep and how fast you got there. The CDC considers any unacclimatized traveler sleeping at 8,000 feet (2,450 m) or higher to be at risk, "and sometimes lower" (CDC Yellow Book). Here is what that means for the heights people actually type into search.

Can you get altitude sickness at 5,000 feet, or in Denver?

Altitude sickness at 5,000 feet is uncommon. Denver sits at about 5,280 feet (1,609 m), well below the 8,000-foot line where the CDC puts the main risk, and the Colorado survey that found 25% AMS was done at resorts between 6,300 and 9,700 feet. What most visitors to Denver notice is milder: getting winded faster on a run or a flight of stairs, a slightly faster heartbeat. The American Heart Association notes that maximal oxygen uptake falls by roughly 1% for every 100 m above 1,500 m (doi.org), so in Denver the hit to your top fitness is small. If you feel unwell in Denver itself, it is worth considering other causes, too.

Is 6,000–8,000 feet high enough to get altitude sickness?

Yes, it can be, especially if you sleep there the night you arrive. Mexico City (about 7,350 feet, 2,240 m) and many mountain towns fall in this band. The Colorado survey that found AMS in a quarter of visitors overall included resorts from 6,300 feet up (doi.org). Cases at this height tend to be mild AMS rather than HAPE or HACE, which become more common higher up. Light activity on the first day and no alcohol for the first 48 hours are the CDC's basic first steps.

Symptoms of altitude sickness at 9,000 feet

At 8,000–10,000 feet (2,450–3,050 m), the height of many ski resorts, altitude sickness symptoms are classic AMS: headache, poor appetite, fatigue, poor sleep. The CDC lists lodgings in Vail at about 8,150 feet (2,480 m) and Breckenridge at 9,600 feet (2,925 m) (CDC Yellow Book). Its risk table counts sleeping below 9,000 feet (2,750 m) on day 1 as lower risk, and advises against going from below 4,000 feet to a sleeping altitude above 9,000 feet in a single day. Flying from the coast and sleeping at Breckenridge the same night is exactly that jump.

Altitude sickness above 10,000 feet: Cusco, La Paz and treks

Above about 11,150 feet (3,400 m) on day 1, the CDC puts travelers in its high-risk category. Cusco (about 11,150 feet, 3,400 m) and La Paz (about 12,000 feet, 3,650 m) are reached by plane, so people go from sea level to that height in a couple of hours. The CDC suggests a workaround for both: descend to sleep lower than the airport for 1–2 nights, then come back up. Above about 9,000 feet (2,700 m), some periodic breathing during sleep becomes nearly universal. Above 14,000 feet (4,300 m), HAPE is no longer a rarity, and the ascent rules below matter much more.

What is a normal oxygen saturation at high altitude?

A normal oxygen saturation at altitude is lower than at sea level, and a reading below sea-level norms is expected, not a sign of illness on its own. The best reference data come from a 2018 study of 6,289 healthy people at 15 locations in the Peruvian Andes, from sea level to 5,100 m (doi.org). The median readings (and the middle half of readings) were:

• 154 m (505 ft) — 99% (98–99)

• 1,400 m (4,600 ft) — 98% (97–99)

• 2,000 m (6,560 ft) — 97% (96–98)

• 2,335 m (7,660 ft) — 97% (96–99)

• 2,500 m (8,200 ft) — 96% (95–97)

• 2,880 m (9,450 ft) — 95% (94–96)

• 3,600 m (11,800 ft) — 92% (90–93)

• 3,950 m (12,960 ft) — 90% (88–91)

• 4,100–4,500 m (13,450–14,760 ft) — 87% (85–89)

• 5,100 m (16,730 ft) — 81% (78–84)

An important limit: these were people who had lived at that altitude for at least 2 months — Andean natives and Hispanic residents. The authors state that their numbers do not apply to non-acclimatized people. Visitors in their first days usually read lower: the CDC notes that acute exposure at about 10,000 feet can bring saturation to 88–91% (CDC Yellow Book), while acclimatized residents near that height had a median of 95%.

Is 95%, 92% or 90% oxygen normal at altitude?

Is 97% or 98% normal in Denver? Yes. Residents at 1,400 m (4,600 ft) had a median of 98% and at 2,000 m (6,560 ft) a median of 97%, so readings in that range at 5,000–6,000 feet are what you would expect.

What is a normal oxygen saturation at 8,000 feet? Acclimatized residents at 2,500 m (8,200 ft) had a median of 96%, with the middle half between 95% and 97%. A newcomer reading a little below that in the first days fits the general pattern that visitors read lower than residents. At 2,300 meters — a common search — residents at 2,335 m had a median of 97%.

Is 92% or 90% oxygen normal at 10,000 feet? For a visitor, it can be. Residents at 2,880 m (9,450 ft) had a median of 95%, but the CDC notes that acute exposure at about 10,000 feet can bring saturation to 88–91%. A reading of 90–92% on your first day there, with no breathlessness at rest and a clear head, is close to that range.

Is 88% oxygen normal in Cusco or La Paz? At 3,600 m (11,800 ft), residents had a median of 92% (middle half 90–93%), and at 3,950 m (12,960 ft) a median of 90%. Newcomers typically sit below residents, so a reading in the high 80s on arrival is not unusual on its own. What matters more is how you feel and whether the number keeps falling at rest.

Does a low SpO2 reading mean I have altitude sickness?

No. Altitude sickness is diagnosed by symptoms, not by a number. The CDC notes that in AMS, pulse oximetry is usually within the normal range for the altitude or only slightly lower, while a high saturation for the altitude seems to be protective (CDC Yellow Book). A 2024 systematic review of 7 studies covering 1,406 people ascending to 3,952–6,300 m found that falling saturation during ascent did have some predictive relationship with AMS, but the studies were too different to give a reliable cut-off (doi.org).

Readings at altitude are also easy to get wrong. A review of pulse oximetry at high altitude points out that saturation changes quickly with small changes in oxygen, that device accuracy falls below 80%, and that cold fingers, bright light and a poorly fitting probe cause errors. Its advice: treat normal values as a range, not a single number, and do not make decisions based on small differences between readings or between people (doi.org). Warm your hand, sit still for a minute, and repeat. For the basics of reading a finger oximeter, see how to measure blood oxygen.

What does deserve attention is a reading that keeps falling while you rest, or any reading alongside breathlessness at rest, confusion or a worsening cough. Those are the emergency signs above, whatever the number says. For sea-level norms and what counts as low there, see our guides to normal blood oxygen levels and low blood oxygen.

At what altitude do you need oxygen?

Healthy travelers do not routinely need supplemental oxygen at the heights where people ski, hike or sightsee. Oxygen is a treatment: the Wilderness Medical Society recommends it for AMS, HACE and HAPE, enough to raise saturation above 90% or relieve symptoms, while waiting to descend or when descent is not possible (doi.org), and the CDC notes it eases an altitude headache within about 30 minutes. For pilots, the US rules are specific: crews must use supplemental oxygen at cabin altitudes above 12,500 feet for flights of more than 30 minutes and at all times above 14,000 feet, and every occupant must be provided with it above 15,000 feet (eCFR). Airliner cabins are designed to stay at a pressure altitude of no more than 8,000 feet (eCFR). If you have lung or heart disease, ask your doctor before the trip.

Is there an SpO2 altitude chart or calculator by age?

The Andean study above published percentile charts by age group (1–5, 6–17, 18–50 and 51–80 years) and found that altitude lowered saturation in every age group (doi.org). We could not find a validated online "calculator" that turns your age and altitude into a personal target, and the review of oximetry at altitude warns that the normal value at a given height is not known with certainty (doi.org). Use the chart as a rough guide, and compare your readings with your own earlier readings on the same trip.

What happens to your heart rate, HRV and sleep at altitude?

Oxygen is only part of the story. Your heart and nervous system respond within hours, and a wearable can show those changes in the first day or two.

Heart rate rises. The American Heart Association explains that sympathetic (stress-system) activity increases in proportion to the lack of oxygen, and that heart rate, stroke volume and cardiac output rise in the first minutes to hours. Over days to weeks of acclimatization, these settle back to sea-level values or below. Blood pressure often dips at first and then may rise above sea-level values during the stay (doi.org). In a simulated ascent to the height of Everest over 40 days, resting heart rate in healthy people rose from 63 bpm at sea level to 89 bpm at the top, without significant arrhythmias. The practical point: a resting heart rate that is several beats higher than your usual on the first mornings is an expected response, not a sign that something is wrong with your heart. For context on everyday ranges, see what a normal resting heart rate is.

HRV falls. A 2025 meta-analysis of 15 studies with 698 healthy adults who went to at least 2,500 m for up to 7 days found that heart rate variability — including RMSSD, the measure Welltory's HRV score is built on — was significantly lower than at sea level. Trained people showed the same drop in RMSSD as everyone else (doi.org). A low HRV score on your first mornings in the mountains reflects the stress of thin air, not a failed workout plan.

Sleep gets lighter and breathing gets uneven. Above about 9,000 feet (2,700 m), some periodic breathing — cycles of deeper breaths, shallow breaths and short pauses — becomes nearly universal, and oxygen levels are lowest during sleep (CDC Yellow Book). That is why you may wake up several times, feel you are gasping on waking, and see more dips in your overnight oxygen chart. It is also why the CDC notes that day trips with an evening return to lower ground are much less stressful on the body.

Take the first day seriously. The AHA statement notes that more than 50% of sudden cardiac deaths at altitude happen on the first day, and that even 1 night above 1,000 m appears to reduce the risk. Fainting is also common at moderate altitudes such as 2,700 m, typically within 24 hours of ascent. For most healthy people this is a reason for an easy first day, not for fear.

How to prevent altitude sickness

Preventing altitude sickness comes down to one thing: giving your body time. The Wilderness Medical Society gives gradual ascent a strong recommendation (doi.org), and the CDC translates it into specific rules (CDC Yellow Book):

• Do not go from below 4,000 feet (1,200 m) to a sleeping altitude above 9,000 feet (2,750 m) in one day.

• Above about 9,800 feet (3,000 m), raise your sleeping altitude by no more than 1,600 feet (500 m) a day, and plan an extra acclimatization day for every additional 3,300 feet (1,000 m); the Wilderness Medical Society adds a rest day, with no gain in sleeping altitude, every 3–4 days.

• Keep exercise mild for the first 48 hours and avoid alcohol for the first 48 hours.

• Never go higher to sleep while you have symptoms, however minor they seem.

• "Climb high, sleep low" works for flights too: for Cusco and La Paz, the CDC suggests sleeping lower than the airport for 1–2 nights first.

Driving beats flying, when you can. Spending a night partway up — for example in Denver before heading to a 9,600-foot resort — breaks the jump into steps. A day trip up and back to sleep lower is gentler still.

How to avoid altitude sickness in Denver

Denver itself is rarely the problem; it is the night you sleep higher. A practical plan for a Colorado trip: spend your first night in Denver, keep the first ski or hiking day easy, skip alcohol for 48 hours, and eat even if your appetite is low. If you have had AMS before, or you are flying in and going straight to a resort above 9,000 feet, ask your doctor ahead of time whether preventive medicine makes sense for you.

Altitude sickness medication, in general terms

Acetazolamide is the main preventive medicine. It is a prescription drug, and the Wilderness Medical Society strongly recommends considering it for travelers at moderate or high risk of AMS (doi.org). The CDC notes it also helps periodic breathing at night. Whether you need it, and how to take it, is a conversation for your doctor before the trip. Dexamethasone, a prescription steroid, prevents and treats AMS and HACE according to the CDC, and the 2024 guideline lists it as an alternative to acetazolamide for adults at moderate or high risk.

Painkillers treat the headache, not the low oxygen behind it. The 2024 guideline recommends that ibuprofen and acetaminophen (paracetamol) can be used to treat headache at high altitude; it recommends against acetaminophen for preventing AMS and suggests ibuprofen for prevention only for people who cannot or do not wish to take acetazolamide or dexamethasone. A painkiller that hides your headache is not a reason to keep climbing. The same guideline does not recommend ginkgo biloba, inhaled budesonide or sleeping in hypoxic tents before a trip.

Does Dramamine help with altitude sickness?

Dramamine (dimenhydrinate) is an antihistamine sold for motion sickness, not altitude sickness. We found no trial showing it prevents or treats acute mountain sickness. The CDC does mention anti-nausea medicine as part of self-treatment for mild AMS, but its example is ondansetron, not dimenhydrinate, and an anti-nausea pill only eases one symptom (CDC Yellow Book). It does nothing for the cause, which is low oxygen. Dimenhydrinate commonly causes drowsiness, and drowsiness at altitude is a symptom you want to be able to read clearly, because it is also a sign of HACE. If nausea is the main problem, ask a pharmacist or doctor what suits you.

Living with altitude sickness: the questions people ask next

Once you know what altitude sickness is, the practical questions start: what to drink, whether to ski on day one, and why you still feel off after getting home.

Can I drink alcohol or coffee at altitude?

The CDC advises avoiding alcohol for the first 48 hours at high altitude, and says respiratory depressants such as alcohol and opiates should not be used to help you sleep there (CDC Yellow Book). The American Heart Association adds that alcohol reduces the drive to breathe and makes the upper airway more likely to collapse during sleep, and links alcohol with a higher risk of sleep apnea (doi.org). A hangover also looks a lot like altitude sickness, which makes symptoms harder to read. Coffee is less studied, and the CDC chapter gives no caffeine advice. A practical approach is to keep to your usual amount rather than cutting it suddenly, since skipping your regular coffee can bring on a withdrawal headache that is easy to mistake for altitude.

Does drinking more water prevent altitude sickness?

Drinking extra water is not a proven way to prevent altitude sickness. The CDC chapter's prevention advice is about ascent rate, alcohol, exertion and medicines; it does not list extra fluids (CDC Yellow Book). The Wilderness Medical Society guideline goes further: forced hydration has never been shown to prevent altitude illness and might raise the risk of low blood sodium (doi.org). Dehydration still matters, because the same chapter lists it among the common look-alikes of AMS, and the American Heart Association names dehydration as one of the extra stressors at altitude for people with heart disease (doi.org). A practical approach is to drink to thirst, check that your urine is pale, and not force liters of water. If you want to know how dehydration affects your heart rate and blood pressure, see can dehydration cause high blood pressure.

Can I ski, hike or work out on my first day at altitude?

You can, but the CDC advises only mild exercise for the first 48 hours (CDC Yellow Book). Your top-end fitness is reduced too: the AHA statement notes that maximal oxygen uptake drops by about 1% for every 100 m above 1,500 m, and one study of downhill skiers found two-thirds had a heart rate above 80% of their predicted maximum while skiing (doi.org). By that rule of thumb, at 9,600 feet (2,925 m) your ceiling is roughly 14% lower than at home. A practical approach is shorter runs, more breaks, and turning back at the first sign of a worsening headache.

Can you get altitude sickness after returning home? Is reverse altitude sickness real?

Acute mountain sickness improves with descent. The CDC notes that going down 1,000 feet (300 m) or more often relieves symptoms (CDC Yellow Book), so feeling worse after you return to sea level is not typical of altitude sickness itself. "Reverse altitude sickness" is not a diagnosis used in the CDC chapter or the Wilderness Medical Society guideline, and we found little reliable research on it after a short trip. If you feel tired and foggy after a mountain holiday, a practical approach is to look at ordinary explanations first: long travel days, short nights, a change of time zone, or a cold picked up on the way. If you have a cough, breathlessness or chest pain after returning, see a doctor rather than waiting it out.

Is altitude sickness risky with a heart or lung condition, or in pregnancy?

The CDC advises that people with coronary artery disease, any chronic lung disease or low baseline oxygen, obstructive sleep apnea or sickle cell trait — even if well controlled — talk to a doctor familiar with altitude before going high (CDC Yellow Book). The American Heart Association says that people with coronary artery disease who have no symptoms at sea level can generally tolerate exercise at moderate altitudes, and stresses acclimatizing before exercise (doi.org). For pregnancy, the CDC suggests it may be prudent not to stay at sleeping altitudes above 10,000 feet (3,050 m). The wording is cautious rather than firm, so this is one to plan with your obstetric team.

Is it altitude sickness, or something else?

Altitude sickness symptoms are nonspecific. The CDC calls the list of look-alikes broad and names the common ones: alcohol hangover, carbon monoxide poisoning, dehydration, drug intoxication, exhaustion, low blood sodium and migraine (CDC Yellow Book). Timing is the best clue. AMS usually starts 2–12 hours after arrival and eases within 12–48 hours if you stay at the same height. Symptoms that begin days later, come with fever, or stay the same when you go down point elsewhere. A practical approach is to treat a new headache at altitude as altitude sickness until it settles, because the CDC's rule is never to go higher to sleep while you have symptoms.

Why do I feel embarrassed or anxious about getting altitude sickness?

Altitude sickness often strikes on a trip you planned and paid for, next to friends who seem fine, and it is easy to feel like the weak one. It is not weakness. The CDC states that fitness does not change the risk, and in Colorado a quarter of ordinary visitors got AMS (doi.org). Some people also feel anxious at altitude because a racing heart and breathlessness feel like panic — you are not imagining those sensations, they are the body's normal response to thin air. If worry about the next trip is heavy, talk it through with your doctor and plan a slower ascent.

How to bring this up with your doctor

Most people never need a doctor for altitude sickness. Book a visit before the trip if you have had moderate or severe AMS, HAPE or HACE before, if you are flying straight to 9,000 feet or higher, if you have a heart or lung condition, sleep apnea or sickle cell trait, or if you are pregnant.

Who to see: your primary care clinician, or a travel medicine clinic. The CDC Yellow Book is written for these clinicians, so it is reasonable to ask them to use it.

What to bring:

• Your itinerary in numbers: where you will sleep each night and at what altitude.

• Your history: any previous trips to altitude, the height you reached, and what symptoms you had.

• Everything you take, including painkillers, sleep aids and supplements.

• Your baseline, if you track it: usual resting heart rate, usual sleep, and your usual SpO2 at home.

What to say: "I'm going to [place] at [altitude], arriving by [plane/car], and sleeping at [altitude] on the first night. Last time at altitude I had [symptoms]. I'd like a plan for preventing altitude sickness and knowing when to go down."

What to ask:

• "Is my ascent plan low, medium or high risk?"

• "Should I take preventive medicine, and are there side effects or interactions with what I already take?"

• "What should I do if I get a headache — and at what point do I need to descend?"

• "Is it safe for me to fly or sleep at altitude with my condition?"

• "Is a pulse oximeter useful for me, and what reading would worry you?"

After the trip: if you had a cough, breathlessness or chest symptoms at altitude, or symptoms that did not settle after you came down, tell your doctor. A note of the altitude, dates and what you felt will help more than memory.

Before you blame yourself, check what your body already recorded

Altitude sickness has a way of feeling personal. I'm out of shape. Everyone else is fine. I'm ruining the trip. People say it to themselves while lying in a dark hotel room with a pounding headache on the first afternoon.

Look at what your body was dealing with instead of the verdict. You may have woken at 4 a.m. for a flight, gone from sea level to nearly 10,000 feet in an afternoon, and slept your first night in air with only about 69% of the sea-level oxygen pressure. On that first morning, your watch likely recorded a faster resting heart rate, a lower HRV and a broken night with more wake-ups — the same pattern the research above describes in healthy people. That is altitude, not character.

It is not your fault, and it says nothing about your fitness. The risk is set mostly by how high you sleep and how quickly you got there.

So give yourself permission, and pick one lever. For most people the most effective one is where you sleep on the first night: one night lower before going higher, or a day trip instead of an overnight stay at the top. On your next trip, change that one thing, and watch the trend for 1–2 weeks around it — resting heart rate settling back, HRV recovering, nights becoming more stable. The trend over the trip tells you far more than any single reading on the first morning.

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How Welltory helps — and what it cannot do

The limits first: Welltory is a general wellness product, not a medical device, holds no regulatory clearance, and does not detect, diagnose, predict or treat altitude sickness. It cannot measure your blood oxygen itself, and it cannot tell you whether a headache is AMS or whether you are safe to go higher. If you have any emergency sign, go down and get help — do not check an app.

What it can show is how your body responded to the trip. Welltory keeps and charts SpO2 that comes from a pulse oximeter or watch through Apple Health, Health Connect or Samsung Health. You will find it in My data → Health, and if a correlation with your HRV, workouts or activity shows up, it appears in the Weeks or Months tabs. With an Apple Watch or Oura on iOS, the Today screen also shows Health (built on today's HRV compared with your 60-day baseline), Battery (with morning charge based on resting heart rate on waking and your sleep) and Stress.

Mark the trip as it happens. When Welltory flags a stress episode and asks "What happened?", tap a tag, type or just talk: "arrived in Denver", "flight to Cusco", "hike to 3,000 m", "headache", "couldn't sleep". Tags only count when they are attached to a stress or rest episode, not to a standalone journal entry. One honest note: at altitude your resting heart rate runs higher, so periods of sitting still may register as stress even when you feel calm. That may reflect the altitude rather than anxiety.

Compare the first nights with your home baseline. With an Apple Watch, Sleep Analysis shows your sleep stages, how many times you woke and how long each awakening lasted (Sleep Stability), and a Breathing chart built from the respiratory rate and blood oxygen your watch recorded. Look at the first 2–3 nights at altitude next to a usual week at home: resting heart rate, HRV, wake-ups, Battery. As you acclimatize, heart rate is expected to settle back over days to weeks, and seeing that in your own data can be reassuring.

My Patterns is for repeat travelers. My Patterns shows which tagged situations tend to come before stressful stretches and which ones "don't happen often but hit your body hard". Insights need at least 7 occurrences of a tag in the current month, plus some history from the month before — so a single week-long trip will not fill it, but a season of ski weekends might.

Build a personal log for your doctor. Your tags, dates and charts make a timeline: where you slept, how your heart rate and sleep looked, and when symptoms began. From the Welltory web app you can export your data as a CSV file (Dashboard → choose a chart → Export) to bring to a pre-trip appointment.

The patterns you find are associations to discuss with your doctor, not proof of whether you had altitude sickness or how you will do next time.

How we made it

Made with AI tools, then edited and fact-checked by the Welltory team. See our Editorial & AI policy.

Data analysis by Jane Smorodnikova, co-founder of Welltory and the person who built the methodology behind how we read physiological data.

Written by Tatsiana Yashyna.

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