Altitude sickness, also known as acute mountain sickness (AMS), occurs when the body struggles to adjust to lower oxygen levels at high altitudes, typically above 2,500 metres (8,000 feet). The condition develops as the air becomes thinner and contains less oxygen, making it harder for the body to deliver sufficient oxygen to tissues. It can affect anyone, regardless of age, fitness level, or previous experience at high altitude. Symptoms usually appear within a few hours of ascent and vary in severity depending on how quickly a person climbs and how well their body acclimatises.
Common symptoms of altitude sickness include headaches, nausea, dizziness, fatigue, and shortness of breath. Some individuals may also experience difficulty sleeping, loss of appetite, or swelling of the hands, feet, and face. These symptoms often feel similar to a hangover and may worsen at night. In most cases, symptoms are mild and improve as the body adapts, but if ignored, they can progress to more serious conditions such as high-altitude cerebral oedema (HACE) or high-altitude pulmonary oedema (HAPE), which can be life-threatening.
The main cause of altitude sickness is ascending too quickly without allowing the body time to acclimatise. As altitude increases, the body needs time to produce more red blood cells to carry oxygen more efficiently. Rapid ascent, dehydration, and physical exertion increase the likelihood of developing symptoms. Cold weather and lack of rest can also add strain to the body’s ability to adapt.
Prevention is key when travelling to high altitudes. Ascending gradually, allowing for rest days every few hundred metres of elevation gain, helps the body adjust naturally. Staying well-hydrated, eating nutritious meals, and avoiding alcohol and strenuous exercise during early stages of acclimatisation can reduce risk. Listening to the body is essential—if symptoms appear, pausing ascent or descending slightly can prevent worsening of the condition.
People who spend extended periods at high altitudes often find that their tolerance improves with repeated exposure. Many mountaineers, trekkers, and travellers take time to “climb high, sleep low,” a method that involves ascending during the day but sleeping at lower elevations to encourage gradual adaptation. Maintaining a slow and steady pace is one of the most effective ways to prevent altitude-related problems.
Most cases of mild altitude sickness resolve within a day or two once the body adapts or descent occurs. However, it is important not to ignore early warning signs. Severe cases can lead to confusion, difficulty walking, or shortness of breath even at rest, which require immediate descent and medical attention. With proper preparation and awareness, most people can safely enjoy high-altitude travel and activities without serious issues.
