What are the symptoms of altitude sickness?
A headache, plus an upset stomach, tiredness or dizziness, usually starting 2 to 12 hours after you arrive somewhere high. The CDC says it feels like a hangover. Don’t go higher to sleep while you have symptoms, and go down if they get worse.
What we’d do
Score yourself each morning with the check below, and believe the score over your oximeter. A yes means no going higher today. Getting worse despite rest, or any confusion, stumbling or unusual breathlessness, means going down now and getting help.
How do you score it?
Mountain doctors use the 2018 Lake Louise score. It has four symptoms, each scored 0 to 3:
| Symptom | 0 | 1 | 2 | 3 |
|---|---|---|---|---|
| Headache | None | Mild | Moderate | Severe, can’t function |
| Stomach | Good appetite | Poor appetite or nausea | Moderate nausea or vomiting | Severe, can’t function |
| Tiredness or weakness | Not tired or weak | Mild | Moderate | Severe, can’t function |
| Dizziness or light-headedness | None | Mild | Moderate | Severe, can’t function |
After a recent climb, and after at least 6 hours at the new elevation, 3 points or more with at least 1 from headache means altitude sickness. The 2018 update took out the old question about sleep, because the experts decided poor sleep up high is more likely a direct effect of the thin air than a symptom of the illness.
When is it serious?
The CDC describes two dangerous forms. Swelling in the brain shows up as confusion, poor coordination (stumbling, trouble walking a straight line) and drowsiness. Fluid in the lungs starts with chest congestion, a cough, breathlessness far beyond what you’re doing, and being able to do less than usual. Either one means going down and getting medical help right away, and the CDC says blood oxygen of 50 to 70 is common with fluid in the lungs.
Ordinary altitude sickness gets better quickly with a descent of 1,000 feet (300 m) or more, the CDC says. Its three rules:
- Never go higher to sleep while you have symptoms.
- Go down if the symptoms get worse, even with rest.
- Going down about 1,000 feet usually helps fast.
Why doesn’t your oximeter catch it?
The CDC says people with altitude sickness usually show a number that’s normal for the altitude, or only a little lower. Everyone’s number drops up high, sick or not, so a low one doesn’t tell you much and a normal one doesn’t clear you. Watches also struggle up there: at 14,957 feet, a Garmin showed about 7 points too high on average, in 13 healthy lowlanders.
Who gets it?
In a study of 3,158 adult visitors to Colorado resorts between 6,300 and 9,700 feet, a quarter got altitude sickness, and two thirds of those within 12 hours of arriving. People who lived below 3,000 feet were 3.5 times as likely to get it, people who’d had it before 2.8 times, and people under 60 twice as likely as older visitors. Rates were also higher in women, in people with obesity, in people with poor or average fitness, and in people with lung disease.
4 sources
- CDC Yellow Book, High-Altitude Travel and Altitude Illness, updated April 23, 2025cdc.gov
- Roach RC and others, The 2018 Lake Louise Acute Mountain Sickness Score, High Altitude Medicine and Biology, 2018pmc.ncbi.nlm.nih.gov
- Honigman B and others, Acute mountain sickness in a general tourist population at moderate altitudes, Annals of Internal Medicine, 1993europepmc.org
- Schiefer LM and others, Validity of peripheral oxygen saturation measurements with the Garmin Fenix 5X Plus wearable device at 4559 m, Sensors, 2021europepmc.org
