Causes of high altitude sickness

As altitude rises, each breath provides less available oxygen. The body needs time to increase breathing and circulation, and a rapid ascent can outpace that adjustment. Risk is higher when someone goes up quickly, sleeps at a higher level, or has had altitude illness before. Early symptoms commonly include [Headache](/symptoms/headache/), dizziness, tiredness, poor sleep, reduced appetite, and [Nausea](/symptoms/nausea/). Worsening breathlessness at rest, confusion, inability to walk normally, or a cough producing frothy sputum can signal a dangerous form of altitude illness.

Do not ascend further while symptoms are present. Rest, keep warm, avoid alcohol and sedatives, and tell a companion. If symptoms worsen or do not improve, descend with assistance; descent is the key response to serious altitude illness. A clinician may discuss preventive medicine before travel, based on your history and itinerary. A [Travel Health Consultation](/treatments/occupational-and-travel-medicine/travel-health-consultation/) can help plan gradual ascent, acclimatisation days, and an emergency route. Do not rely on fitness or previous travel as proof that you are protected.

Treat confusion, unusual drowsiness, loss of coordination, severe weakness, breathlessness at rest, chest tightness, or a worsening cough as an emergency. Descend immediately with help and seek emergency medical care. Do not leave a confused or unsteady person alone and do not allow them to continue climbing. Mild headache or nausea can also worsen, so monitor symptoms closely and stop ascent at the first sign of illness.

Ask how quickly to ascend, whether your heart or lung history changes the plan, which medicines are suitable, and what evacuation options exist. Discuss sleeping altitude, prior symptoms, and when to descend rather than waiting for symptoms to become severe.