At any given point, hundreds of thousands of people are in the skies. For many, journeys pass without incident, but for some, a routine flight may trigger a health emergency. A study last year showed that one in every 212 flights experiences some kind of in-flight emergency, compared with one in every 604 flights in 2013. While air travel is one of the safest modes of transport, it places unique challenges on the human body.
Cabin pressure and oxygen levels
The aircraft cabin is pressurised to a level of up to 8,000 feet above sea level. This pressure change affects body systems, especially those containing gases, such as the respiratory and gastrointestinal systems. As cabin pressure decreases, the amount of available oxygen drops because molecules are further apart. At sea level, air contains about 21% oxygen; at altitude, it contains the equivalent of 15% oxygen. The body compensates by increasing breathing and heart rate to pump oxygen to tissues. A healthy person may not notice, but someone with a cardiopulmonary disease, such as chronic obstructive pulmonary disease or hypertension, may be at risk.
Dehydration and fluid loss
Humidity is very low in the cabin, drying out skin, eyes, nose and throat. Passengers lose up to 360ml of water per hour through respiration and skin. This dehydration thickens the blood, making the heart work harder and increasing the risk of clotting-related conditions such as deep vein thrombosis. Alcohol and dehydration, combined with cabin conditions, also contribute to fainting, which occurs in at least one in three airline emergencies. Many of these faints are caused by postural hypotension: standing up causes blood to pool in the legs, reducing brain blood flow.
Food and gastrointestinal issues
At altitude, taste buds are about 30% less sensitive, so foods often have extra salt added for flavour, further contributing to dehydration. Many in-flight complaints involve gastrointestinal issues. When the gut breaks down food, it produces gas, which expands in the plane's low pressure. Intestinal gas can expand to four times normal volume, leading to flatulence—a phenomenon called high altitude flatus expulsion. Foods like beans, broccoli, kale, onions, red meat, lentils and gluten can make it worse. In rare cases, severe stomach upset—'jet belly'—has forced flights to turn around. For example, a 2023 flight from Atlanta to Spain returned to the US after a passenger left a trail of diarrhoea along the aircraft.
Cardiac events and other emergencies
Mid-air cardiac emergencies are rare but have far poorer outcomes than on land. The vast majority of in-flight deaths are due to cardiac events. Reasons include varied and limited in-flight medical equipment and a lack of trained medical professionals. Other vascular events like strokes are also rare but can have poor outcomes for similar reasons.
Safe travel tips
To reduce risks: drink plenty of water before and during the flight; set a schedule for taking medication; move around at least once every couple of hours to maintain blood circulation and prevent muscle stiffness; limit or avoid alcohol, as its effects are magnified at altitude. People who have recently had dental work, surgery or been diving in the days before flying may be at increased risk due to pressure changes and potential gases introduced to the body. Depending on the type of diving, at least 48 hours between diving and flying may be recommended. Not every emergency requires landing; the captain makes that decision based on input from crew and medical professionals.
This research was conducted by Adam Taylor, Professor of Anatomy at Lancaster University. This article is republished from The Conversation under a Creative Commons license.
