At any given moment, hundreds of thousands of people are travelling by air. For most, the journey passes without incident. But for a growing number, a routine flight can trigger a medical emergency. Research published last year found that one in every 212 flights now experiences an in-flight emergency, compared with one in 604 flights in 2013. While air travel remains one of the safest modes of transport, the unique environment of an aircraft cabin places significant strain on the human body.
The primary culprit is cabin pressure. Aircraft cabins are pressurised to the equivalent of up to 8,000 feet above sea level. At this altitude, the available oxygen drops from the 21% found at sea level to around 15%. To compensate, the body breathes faster and the heart pumps harder to deliver oxygen to tissues. A healthy person may not notice, but those with cardiopulmonary conditions such as chronic obstructive pulmonary disease (COPD) or hypertension can face dangerous consequences. The reduced oxygen and pressure changes impair how well the heart and lungs function, potentially triggering serious events.
Dehydration is another major challenge. Cabin humidity is extremely low, drying out the skin, eyes, nose and throat, and causing fluid loss of up to 360ml per hour. This makes the blood thicker, forcing the heart to work even harder, and increases the risk of deep vein thrombosis (DVT). Fainting is one of the most common in-flight emergencies, seen in at least one in three cases. It is often caused by postural hypotension — moving from sitting to standing causes blood to pool in the legs — but alcohol and dehydration create a particularly risky combination.
Gastrointestinal issues are also frequent. As the gut breaks down food, it produces gas that expands to up to four times its normal volume at altitude. This can cause discomfort and flatulence — a phenomenon known as 'high altitude flatus expulsion' — and, in rare cases, severe bloating known as 'jet belly'. Foods such as beans, broccoli, kale, onions, red meat, lentils and gluten can worsen the problem. In one incident in 2023, a flight was forced to turn around due to a severe onboard stomach upset.
For UK travellers, these risks are worth considering before flying. The Foreign, Commonwealth & Development Office (FCDO) advises passengers with pre-existing medical conditions to consult their GP before booking. Travel insurance policies should cover in-flight medical emergencies and repatriation, especially for those with heart or lung conditions. Staying hydrated, avoiding excess alcohol, and eating light, low-gas meals before and during a flight can help reduce discomfort. Compression socks may lower DVT risk on long-haul routes, and moving around the cabin periodically is recommended. New direct routes from UK airports to popular destinations such as Spain, Greece, Turkey, and the United States continue to expand, making awareness of these health considerations increasingly important.