What Is Altitude Sickness?

What is altitude sickness?

Altitude sickness, also called acute mountain sickness, is a condition that can develop when you ascend to a high elevation faster than your body can adjust to the lower oxygen levels found there. At high altitudes, generally above around 8,000 feet, the air pressure is lower and each breath delivers less oxygen, and if you go up too quickly your body may not have time to acclimatize, leading to illness. It commonly affects travelers to high mountain regions, elevated cities, and destinations reached by rapid ascent. Altitude sickness ranges from a mild, common form with flu-like symptoms to rare but severe, life-threatening forms involving fluid in the lungs or brain. Understanding it matters for anyone planning to travel to high elevations, since prevention and early recognition are key to staying safe.

What causes altitude sickness and who gets it?

Altitude sickness is caused by the reduced oxygen and lower air pressure at high elevations, combined with ascending too rapidly for your body to adapt. When you climb high quickly, your body has less time to adjust to the thinner air, and the resulting lack of oxygen triggers symptoms. Importantly, altitude sickness can affect anyone regardless of age, fitness, or health; being physically fit does not prevent it, and previous trips without problems do not guarantee immunity. Risk factors include the speed of ascent, the altitude reached, especially where you sleep, and individual susceptibility, which varies and is hard to predict. Exertion and dehydration can contribute. Because even healthy, experienced travelers can be affected, everyone heading to high altitude should take it seriously and ascend sensibly rather than assuming they are immune.

What are the symptoms of altitude sickness?

The symptoms of mild altitude sickness resemble a hangover and typically appear within hours of arriving at altitude. They include headache, which is the hallmark symptom, along with nausea or vomiting, dizziness, fatigue, loss of appetite, shortness of breath on exertion, and difficulty sleeping. Mild cases usually improve with rest and acclimatization. However, altitude sickness can progress to dangerous forms: high-altitude cerebral edema, involving brain swelling, can cause confusion, loss of coordination, and severe drowsiness, while high-altitude pulmonary edema, involving fluid in the lungs, causes breathlessness at rest, a persistent cough, and extreme weakness. These severe forms are medical emergencies. Warning signs such as confusion, trouble walking, breathlessness at rest, or a bluish tinge to the skin mean the situation is serious and needs immediate action.

How do you prevent and respond to altitude sickness?

The best prevention is to ascend gradually, giving your body time to acclimatize rather than climbing high too fast, and where possible to avoid sleeping at a much higher elevation than the night before. Staying hydrated, avoiding alcohol, and not overexerting on arrival help. If mild symptoms appear, stop ascending, rest, and allow time to acclimatize; do not go higher until you feel better. Crucially, if symptoms are severe or worsening, the essential response is to descend to a lower altitude immediately and seek medical help, as severe altitude sickness can be fatal without prompt action. Some travelers take preventive medication such as acetazolamide, but you should consult a doctor or travel clinic before your trip about whether that is appropriate for you and about safe ascent, especially for high-altitude destinations.