What does a long-haul flight actually do to your body? : ScienceAlert

If crowded airports are any indication, people are eager to get back to the skies. And if you fly long-haul, in a few years you may have an even longer option.

Qantas has announced from the end of 2025 that it will fly passengers on non-stop flights from Australia’s east coast to London that will see you in the air for more than 19 hours at a stretch. This is compared to today’s flights which take most of 24 hours, but which are divided into shorter legs.

So what will happen to your body during one of these longer flights? Is it different to what happens when you fly long-haul now?

1. You can become dehydrated

Dehydration is common on long-haul flights. That may explain why your throat, nose and skin can feel dry on a plane. The longer the flight, the greater the risk of dehydration.

This is due to the low humidity in the cabin compared to what you would expect on the ground. This is mostly because much of the air that circulates through the cabin is drawn from the outside, and there is not much moisture in the air at high altitudes.

You also risk dehydration by not drinking enough water, or drinking too much alcohol (alcohol is a diuretic, resulting in an increase in fluid loss).

So drink water before hopping on the plane. During the flight, you also need to drink more water than you normally would.

2. The cabin can damage the ears, sinuses, intestines and sleep

When cabin pressure changes, the gas in our bodies reacts accordingly. It expands when the plane climbs and the pressure decreases, and the opposite happens when we descend. This can lead to common problems such as:

  • earache – when the air pressure on either side of the eardrum is different, putting pressure on the eardrum
  • headache – can be caused by expanding air trapped in your sinuses
  • stomach problems – just accept that you will fart more.

You may also feel more sleepy than usual. This is because the body is unable to absorb as much oxygen from the cabin air at altitude as it would on the ground. Slowing down is the body’s way of protecting itself, and this can make you feel tired.

The good news is that most of these problems won’t necessarily be more pronounced on longer flights. They are mainly a problem when the aircraft is climbing and descending.

3. You can develop blood clots

Blood clots, associated with being immobile for long periods, are usually a major concern for passengers. These include blood clots that form in the leg (deep vein thrombosis or DVT) that can travel to the lung (where it is known as a pulmonary embolism).

If you don’t move around on the plane, and the more of the following risk factors you have, the greater the chance of a blood clot developing:

  • older age
  • obesity
  • previous history or a family history of blood clots
  • certain types of coagulation disorders
  • cancer
  • recent immobilization or surgery
  • pregnancy or recent birth
  • hormone therapy or birth control pills.

According to a 2022 review, which combined data from 18 studies, the longer you travel, the greater the risk of blood clots. The authors calculated that there was a 26 percent higher risk for every two hours of flying, starting after four hours.

So what about the risk of blood clots on these longer flights? We won’t know for sure until we start studying passengers on them.

Until that evidence comes in, the current advice still applies. Keep moving, stay hydrated and limit alcohol consumption.

There is also evidence for using compression stockings to prevent blood clots. These stockings are said to promote blood flow in the legs and help blood return to the heart. This will normally happen with muscle contractions from movement or walking.

A 2021 Cochrane the review combined the results of nine trials involving 2,637 participants who were randomized to wear compression stockings (or not) on flights lasting more than five hours.

No participants developed symptomatic DVT. But there was evidence that people who wore the stockings greatly reduced the chance of developing blood clots without symptoms, and we know that any blood clot can potentially grow, move and then cause symptoms.

So if you are concerned about the risk of developing blood clots, you should see your GP before you fly.

Usually if you develop a blood clot, you won’t know about it until after the flight, as it takes time to form and travel.

So keep an eye out for symptoms after the flight – pain and swelling in one leg (often just one), chest pain, cough and shortness of breath. And seek emergency medical attention if you do.

4. Then there is jet lag, radiation, COVID

Then there is jet lag, which is foreign to few of us. This is a disconnect between the time your body thinks it is and the time by the clock, when you cross time zones.

Longer flights mean you are more likely (but not always) to cross multiple time zones. Jet lag will usually become more of a problem when you cross three or more, especially if you are traveling east.

And if you take long-haul flights very often, it’s reasonable to assume that the longer you’re in the air, the greater your exposure to cosmic radiation.

As the name suggests, this is radiation coming from space, which can increase the risk of cancer and reproductive problems. We do not know what level of exposure is safe.

But unless you fly frequently, it’s unlikely to be a problem. If you are pregnant or have other concerns, talk to your GP before you fly.

And don’t forget about COVID. Take the usual precautions – wash your hands regularly, wear a mask and do not fly if you are unwell.

In a nutshell

Research into how the body reacts to these longer, direct flights between Australia and Europe is in the early stages. Teams in Australia are looking at this now.

Until then, if you’re taking a regular long-haul flight, the advice is relatively simple.

Follow the advice the airlines give you, and see your GP before you travel if necessary. During the flight, make the extra effort to move around the cabin, drink water, wear a mask and practice good hand hygiene.

And see a doctor immediately for any worrisome post-flight symptoms, as blood clots can take hours or even days to form, grow and travel through your veins.The conversation

Tony Schiemer, Commercial Pilot | Specialist in Aviation Medicine | Clinical Lecturer, University of Adelaide

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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