AMS, HAPE and HACE: three illnesses, not one
AMS makes you feel terrible. HAPE and HACE kill. That is the distinction that matters on the mountain, and it is why the symptom score above only answers the first of the three questions. AMS is a headache plus feeling ill, and it resolves with rest or a modest descent. HAPE is fluid in the lungs and HACE is swelling of the brain, both of which get worse while you wait, and neither of which has a score to fill in.
Acute mountain sickness is what the 2018 Lake Louise score measures: headache, nausea or poor appetite, fatigue, dizziness. It is common, it is not in itself dangerous, and its real significance is as a warning that you have gone up faster than you have adapted. Nobody with AMS should go higher.
HAPE, high altitude pulmonary oedema, is fluid collecting in the lungs. The symptom that separates it from being unfit or tired is breathlessness at rest: not while walking uphill, but sitting still. With it come a dry cough that turns wet, pink or frothy sputum, gurgling breathing, and blue lips or fingernails. HAPE can arrive without any AMS at all, so a low symptom score above is not reassurance. It is the leading cause of death at altitude.
HACE, high altitude cerebral oedema, is swelling of the brain. The distinguishing sign is neurological rather than how bad someone feels: a stumbling, drunk looking walk (ataxia), confusion, personality change, drowsiness sliding towards unconsciousness. The field test is simple and worth knowing before you need it. Ask the person to walk heel to toe along a straight line. If they cannot, treat it as HACE.
The three overlap, and a severe AMS score is not a different illness from early HACE so much as a point on the way to it. That is why the numbers above stop being the question once ataxia or breathlessness at rest appear. At that point there is nothing left to score.
When to descend, with no waiting
Descend immediately, at any hour, in any weather, for any one of these: a stumbling walk, confusion or altered consciousness, or breathlessness while sitting still. These are HACE and HAPE. There is no dose of rest, no drug and no amount of hydration that substitutes for losing altitude, and every hour spent deciding is spent getting worse.
Go down now, do not wait for morning:
- Cannot walk heel to toe in a straight line
- Confusion, strange behaviour, unusual drowsiness
- Breathless at rest, or a wet cough with pink or frothy sputum
- Blue lips or fingernails, gurgling breathing
- Symptoms that are getting worse rather than settling
- Anyone who cannot look after themselves
Two things about descending that people get wrong. The first is company: nobody with suspected HACE or HAPE descends alone, because the illness that makes them stumble is the illness that will decide they are fine. The second is sleeping altitude. Coming down for the evening and then going back up the next morning because the symptoms eased is how a mild problem becomes an evacuation. What counts is where you sleep.
Below that threshold the rule is duller and still worth following. Any AMS at all means you do not go higher that day. Symptoms that are not improving after a rest day mean you go down. Oxygen or a portable hyperbaric bag can buy time when descent is genuinely impossible, and buying time is all they do; they are not an alternative to going down.
What the 2018 Lake Louise score is, and what changed
The Lake Louise score is a four question symptom questionnaire, each answer worth 0 to 3, giving a maximum of 12. AMS is diagnosed when a headache scores at least 1 point and the total reaches 3 or more, after a recent ascent or gain in altitude. The four questions are headache, gastrointestinal symptoms, fatigue or weakness, and dizziness or light-headedness.
Sleep quality is not one of them, and the 2018 Lake Louise AMS Score explains why. Poor sleep at altitude is caused by hypoxia itself rather than by AMS, so it tracks altitude rather than illness. In the 2013 dataset of 292 participants a sleep item correlated poorly with the other four, and leaving it out gives the scale an internal consistency of 0.84 rather than 0.79. And 40 percent of the people reporting a severe headache reported no sleep disturbance at all, which is not how an item belonging to the same syndrome behaves.
This is not a technicality. Bad sleep at altitude is close to universal, so counting it as a symptom hands a diagnosis of AMS to a large share of the people who answer honestly: a mild headache worth 1 point plus a broken night worth 2 reaches the threshold of 3 on its own. Plenty of altitude questionnaires online still score sleep, so a total you get elsewhere may be higher than the one here for that reason alone, and it is worth checking how many questions you were asked.
The severity bands are mild at 3 to 5, moderate at 6 to 9, severe at 10 to 12 points. The committee publishes them as suggestions rather than a validated classification, and says plainly that the studies needed to fix the cut points have not been done. Read them as a rough guide to how much trouble you are in, not as a threshold that means something precise.
So does a terrible night mean AMS?
No, and that is the point of the change. Sleep at altitude is genuinely disturbed: periodic breathing, waking repeatedly, the feeling of not having slept at all. It happens to people with no other symptom of altitude illness, because it comes from hypoxia rather than from AMS, which is exactly why the committee took it out of the score. None of that makes it unimportant. A sleepless night leaves you slower and worse at judging things on ground where judgement matters, and if the nights are getting worse rather than settling as you acclimatise, that is worth paying attention to on its own terms. It just is not a point on this questionnaire.
What the ascent risk band is, and what it is not
The ascent tab returns a band, low through very high, rather than a percentage. Nobody publishes a probability of AMS for a given plan that we could cite. A percentage reads like the output of a cohort study, so printing one would claim a precision that does not exist behind it.
Where these numbers come from
From the guidance quoted elsewhere on this page: AMS is uncommon below 2500 m, risk rises materially above 3000 m and is high above 4000 m for anyone not already acclimatised, and the ascent rate above 3000 m should stay within 300 to 500 m of sleeping altitude per day with a rest day every 1000 m.
Ours, and labelled as ours: mapping those altitudes onto four named bands, counting a gain of double the daily limit twice instead of once, treating a first night at altitude as a step up, and stepping the band back down for somebody who has three nights behind them and is gaining less than 300 m tonight. These are conservative choices, not published cut points, and the result lists which of them fired so you can disagree with any of them.
Two things the band deliberately does not do. It does not add up your risk factors into a score, because the weights would be invented: a previous episode of AMS is the strongest single predictor anyone reports, and nothing else on the old list was in the same category. And it does not rank ages. The retired version gave "age under 25 or over 60" the same weight as everything else, and we could find no source publishing a weight, a direction or even an age band, so the factor is gone rather than guessed at.
Where the band stops being useful, it says so. Above 4000 m (13,100 ft) and past a gain of 1000 m (3,300 ft) in a day the label cannot climb any further, so the result adds a line saying that going higher or faster still raises the risk without moving the band. Above 5500 m it says something stronger: the body does not acclimatise indefinitely up there, and this page does not cover that ground.
How to ascend so this does not happen
Above 3000 m (9,800 ft), gain no more than 300 to 500 m of sleeping altitude per day and take a rest day for every 1000 m gained. In feet that is 1,000 to 1,600 ft a day, with a rest day every 3,300 ft. Those two numbers prevent more altitude illness than everything else on this page put together, because the only variable you control is the rate.
What acclimatises is where you sleep, not where you walked. Climbing high and sleeping low works precisely because of that split: the day at altitude is the stimulus and the night lower down is where the body does the adapting. It is the standard technique on expeditions for a reason, and it is available to anybody whose route allows a descent to camp.
Two other things matter as much as the profile. Flying or driving straight to altitude removes the gradual part of a gradual ascent, so the first days after arriving high are the dangerous ones rather than the last. And your own history is the best predictor there is: somebody who has had AMS before at a given altitude and rate is likely to have it again, and should plan a slower profile rather than assume fitness has fixed it. Fitness does not protect against altitude illness at all.
The oldest rule in the field is still the useful one. If in doubt, do not go up.
Medication, and what this page will not tell you
Acetazolamide is the drug with the best evidence for preventing AMS, dexamethasone is used for HACE and nifedipine for HAPE, and none of them is a substitute for descending. This page deliberately does not print doses or schedules, because the guideline they come from is not one we can cite precisely enough to publish numbers on a page about a condition that kills.
What is worth knowing without a dose. Acetazolamide speeds acclimatisation rather than masking symptoms, and it is a prescription drug in most countries, which means the conversation with a doctor happens before the trip rather than at the trailhead. Ibuprofen and paracetamol treat an altitude headache and do nothing about the AMS underneath it, so a headache that answers to painkillers is not a resolved problem. Dexamethasone and nifedipine are emergency drugs carried by expeditions for HACE and HAPE, and the reason every source pairs them with the word descend is that they buy time on the way down rather than permission to stay up.
For doses, timing and interactions, ask a travel medicine or wilderness medicine practitioner and get it from the current Wilderness Medical Society practice guidelines directly. That is not a hedge. It is the difference between a page that tells you what altitude illness is and a page that prescribes.
Frequently asked questions
What altitude causes altitude sickness?
AMS typically begins above 2500m (8200 ft). Risk increases significantly above 3000m and becomes very high above 4000m. The key factor is not just altitude but ascent rate: gaining more than 500 m (1,600 ft) of sleeping altitude per day above 3000 m (9,800 ft) dramatically increases risk.
What is the Lake Louise Score?
The 2018 Lake Louise AMS Score is the clinical standard for diagnosing acute mountain sickness. It scores four symptoms, headache, gastrointestinal symptoms, fatigue or weakness, and dizziness, from 0 to 3 each, giving a maximum of 12. AMS is diagnosed when headache scores at least 1 point and the total reaches 3 or more after a recent ascent. The 2018 consensus removed the fifth question, sleep disturbance, which is why this calculator scores out of 12 rather than the 15 you will see on older charts.
How fast is safe to ascend?
Above 3000 m (9,800 ft), gain no more than 300-500 m (1,000-1,600 ft) of sleeping altitude per day. Every 1000m gained above 3000m, spend a rest day acclimatizing. The "climb high, sleep low" technique, hiking to higher altitude during the day but returning to sleep lower, is very effective for acclimatization.
When should I descend for altitude sickness?
Descend immediately, at any hour and in any weather, for a stumbling walk, confusion or altered consciousness, which are HACE, or for breathlessness at rest, pink frothy sputum or blue lips, which are HAPE. Do not wait for morning and do not let anyone descend alone. For mild AMS (score 3 to 5 with headache), do not ascend and rest. For moderate AMS (score 6 or more), descend 300-1000m immediately. Symptoms that are getting worse rather than settling are a reason to go down whatever the score says.
What is the difference between AMS and HAPE?
AMS makes you feel ill; HAPE can kill you within a day. AMS is a headache plus nausea, fatigue or dizziness, and it resolves with rest or a modest descent. HAPE is fluid collecting in the lungs, and the symptom that separates it from being tired is breathlessness at rest rather than on exertion, along with a wet cough, pink or frothy sputum, gurgling breathing and blue lips. HAPE can appear with no AMS at all, so a low Lake Louise score is not reassurance. HAPE means immediate descent, not rest.
Does a bad night of sleep mean altitude sickness?
No. Disturbed sleep at altitude comes from hypoxia rather than from AMS, and it happens to people with no other symptom of altitude illness. That is why the 2018 Lake Louise consensus removed sleep disturbance from the score: in the source dataset it correlated poorly with the other symptoms, and 40 percent of people reporting a severe headache reported no sleep disturbance at all. Removing it raised the internal consistency of the scale from 0.79 to 0.84. A bad night still leaves you slower and worse at judging things, so it is worth noticing. It just does not score points and does not by itself mean you have AMS.
Does fitness protect against altitude sickness?
No. Fitness level does not protect against AMS. Well-trained athletes are just as susceptible as unfit individuals. The body's acclimatization response is determined by physiology, not fitness. The best predictor of AMS susceptibility is prior personal history of AMS at altitude.
Does Diamox (acetazolamide) prevent altitude sickness?
Acetazolamide (Diamox) has the best evidence of any drug for reducing AMS risk, and it works by speeding acclimatisation rather than by masking symptoms. This page does not publish doses or schedules, because the guideline they come from is not one we can cite precisely enough to print numbers for a condition that kills. It is a prescription drug in most countries, so the conversation with a doctor happens before the trip. Common side effects include increased urination and tingling in the hands and feet. No drug is a substitute for descending.