Altitude sickness and air travel

Cabin pressure is lower than at sea level, which reduces available oxygen somewhat. Most healthy travellers tolerate this, but people with certain heart or lung conditions may feel breathless or unwell. Headache or nausea in a plane can also come from dehydration, motion sickness, anxiety, migraine, infection or missed meals.

Acute mountain sickness typically follows ascent to a high terrestrial elevation, especially when the body has little time to acclimatise. A pressurised cabin creates a controlled environment and the exposure usually ends when the aircraft lands. This makes the pattern different from sleeping and exercising on a mountain.

Someone who has just descended from high altitude may board while still symptomatic. In that situation, the illness began with the mountain exposure rather than the aircraft. Continuing headache, vomiting, poor balance or breathing trouble should be assessed before flying because access to evaluation is limited in the air.

Tell the cabin crew early, especially if symptoms are new, worsening or accompanied by breathlessness. Sit upright, limit exertion and follow crew instructions. Sip fluids if you are alert and not vomiting, and use only medicines that are suitable for you and carried in their labelled packaging.

Do not assume every in-flight headache is altitude sickness. Note when the symptoms began, whether you recently stayed at high elevation, and whether chest pain, weakness, fever or visual changes are present. This information helps the crew and medical professionals decide what support is needed.

Alert cabin crew immediately for severe breathlessness, chest pain, blue or grey lips, confusion, fainting, a seizure, new one-sided weakness, or inability to walk normally. These are emergency warning signs regardless of whether altitude is the cause. The crew can seek ground-based medical advice and arrange assistance on landing.

A traveller with active severe altitude illness should descend and receive medical care rather than board a routine flight without assessment. Supplemental oxygen needs must be arranged with the airline and treating clinician before travel; a personal plan cannot be improvised safely after boarding.

Ask whether a heart, lung, blood or neurological condition could make cabin oxygen levels harder to tolerate. Discuss recent altitude illness, current symptoms, fitness to fly, medicine timing and whether the airline needs advance documentation for oxygen or mobility support.