What happens to your body on a long flight?

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

Qantas has announced that from the end of 2025 it will carry passengers on direct flights from the east coast of Australia to London this would see you in the air for more than 19 hours per leg. This is compared to current flights which last the best part of 24 hours but are broken up into shorter segments.

So what happens to your body during one of these longer ones flights? Is that any different than what happens when you fly long haul now?

1. You can get dehydrated

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

This is due to the low level of humidity in the cabin compared to what you would expect on the ground. This is mainly because a lot of the air circulating through the cabin is drawn in from the outside and there is not much moisture in the air at high altitudes.

You also risk dehydration by not drinking enough wateror drinking too much alcohol (alcohol is a diuretic, leading to increased fluid loss).

So drink water before jumping on the plane. You will also need to drink more water than you normally would during the flight.

2. The cabin can wreak havoc with your ears, sinuses, intestines, and sleep

As the cabin pressure changes, the gas in our body reacts accordingly. It expands as the aircraft climbs and pressure descends and the opposite occurs when descending. This can lead to common problems such as:

Dehydration is common on long-haul flights (Credit: Getty Images/Thinkstock)

*ear pain – when the air pressure on both sides of your eardrum is different, apply pressure to the eardrum
*headaches – can be caused by expanding air trapped in your sinuses
*intestinal problems – just accept the fact that you’re going to fart more.

You may also feel sleepier 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, which is why you may feel sleepy.

The good news is that most of these problems aren’t necessarily more pronounced on longer flights. The problem is mainly when the plane climbs and descends.

3. You could develop blood clots

Blood clots, associated with long periods of immobility, are usually a big problem for travelers. These include clots that form in the leg (deep vein thrombosis or DVT) that can travel to the lungs (where this is known as a pulmonary embolism).

If you don’t move around on a plane and the more of the following risk factors you have, the more likely you are to develop blood clots:

*previous history or family history of clots of certain types of clotting disorders
*recent immobilization or surgery
*pregnancy or recent birth
*hormone replacement therapy or the oral contraceptive pill.

The longer, according to a 2022 review that combined data from 18 studies travel, the greater the risk of blood clots. The authors calculated that for every two hours of air travel, starting after four hours, the risk was 26% higher.

So what about the risk of precipitation 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 stands. Keep moving, stay hydrated and limit alcohol consumption.

There is also evidence of wearing compression stockings to prevent blood clots. These stockings are said to promote blood flow in the legs and help return blood to the heart. This would normally happen with muscle contractions when moving or walking.

Jet lag will usually be more of an issue when you exceed three or more, especially if you’re traveling east (Credit: Getty Images/Thinkstock)

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

None of the participants developed symptomatic DVT. However, there is evidence that people who wore stockings greatly reduced their chance of developing clots without symptoms, and we know that any clot can potentially grow, move and subsequently cause symptoms.

So if you are concerned about the risk of blood clots, visit your GP before your flight.

Usually, if you develop a blood clot, you won’t know about it until after the flight because the clot takes time to form and travel. Therefore, watch for symptoms after the flight – pain and edema in the leg (often just one), chest pain, cough and shortness of breath. And if so, seek emergency medical care.

4. Then there’s jet lag, radiation, COVID

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

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

And if you take long flights very often, it’s reasonable to assume that the longer you’re in the air, the greater your exposure to cosmic rays. As the name suggests, this is radiation from space that can increase the risk of developing cancer and reproductive problems. We don’t know what level of exposure is safe.

However, if you don’t fly often, this probably won’t be a problem. If you are pregnant or have other concerns, talk to your GP before you fly.

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

In a nutshell

Research into how the body responds to these longer non-stop flights between Australia and Europe is at an early stage. Teams in Australia are now looking at it.

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

Follow the advice given by the airlines and, if necessary, see your GP before travelling. During the flight, try to move around the cabin, drink water, wear a mask and observe proper hand hygiene.

And see a doctor right after your flight for any worrisome symptoms, because blood clots can take hours or even days to form, grow, and move along your veins.

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