What happens to your body on a long-haul flight?

Travelers spend many hours in the air on their way to distant countries. We reveal what a long-haul flight does to your body and how you can prevent negative effects.

Wanderlust knows no bounds - and sometimes that means spending many hours in the air. Those who want to reach dream destinations must be patient: Before you can lay out your beach towel or go sightseeing, a long flight awaits.

On the way to far-off destinations like the USA, Australia, or South Africa, you might often spend at least half a day in the plane. The current longest nonstop flight in the world from Singapore to New York takes a full 18 hours and 45 minutes. Airlines like Qantas are planning nonstop flights from the Australian east coast to London, which are expected to last more than 19 hours straight.

If you've ever taken a long-haul flight, you've likely noticed: Such a long flight impacts the body. Eventually, your legs become stiff, many people experience ear pain or stomach discomfort.

The travel writer spoke with Prof. Dr. Thomas Weiss, a specialist in internal medicine at the Diakovere Henriettenstift in Hanover. We explain what a long-haul flight does to your body.

In the airplane, you are many meters above the earth. In high altitudes, your body absorbs less oxygen. This decreases the oxygen saturation in your blood. According to Dr. Weiss, it is between 97 and 98 percent at sea level. During a flight, it is only about 91 percent.

'For a healthy person, the reduction does not matter,' explains the internist. 'They can compensate through adjustments in heart and breathing rates.' But for people who struggle with low air at ground level, oxygen deficiency worsens on the plane, 'and a feeling of breathlessness can arise.' People with heart failure or restricted heart circulation may also experience problems on long flights.

When air pressure decreases during takeoff and landing, it can create an uncomfortable feeling in the middle ear and sinuses.

Onboard an airplane, the air is quite dry, with humidity levels at about 5 to 15 percent. This can make your nasal membranes feel dry and irritate your eyes. 'A blocked nose and swollen passages between the throat and middle ear then intensify issues with pressure balance,' says Dr. Weiss.

Also, taste perception changes in the air: Because blood is not as well oxygenated, your ability to perceive smells and taste receptors diminishes, similar to having a cold. That's why airplane food often tastes bland and dull.

Harmless but at times very unpleasant is another effect of the low pressure in the cabin: Pre-existing gases in the body expand when the pressure decreases. 'This can lead to a feeling of fullness, belching, or bloating,' explains the doctor.

During a flight, you spend many hours sitting continuously. If you haven't booked a seat in First Class, you have limited opportunities to move around or stretch your legs. Prolonged sitting slows blood flow and causes water to accumulate in the legs.

Additionally, the low humidity and oxygen levels in the cabin contribute to blood becoming thicker and flowing slower. Feet and calves can swell. And: 'The combination of slowed blood flow and obstructed return flow due to cramped sitting positions with bent legs can lead to a thrombosis in the veins of the leg,' says Dr. Weiss.

This can become dangerous if the clot is carried away by the blood flow and moves toward the heart and lungs. There, it can cause a pulmonary embolism - a potentially life-threatening condition.

The higher a plane flies, the greater the exposure to cosmic radiation, also known as cosmic rays. However, according to Dr. Weiss, you needn't worry about this. 'Cosmic radiation poses no problem for occasional flyers, nor for children and pregnant women,' assures the doctor.

With lower oxygen saturation and humidity levels and falling pressure, the body is naturally exposed to these factors on a short-haul flight just as it is on a long-haul flight. The effects are milder on a short flight, explains Dr. Weiss.

Even the cramped seating has less of an impact on blood flow during a short-haul flight. The risk of thrombosis increases with flight duration, the doctor says. 'For flight times under four hours, this risk is considered very low, but it increases significantly after eight hours.'

To make a long-haul flight as comfortable as possible for your body, you should drink plenty of fluids like water or juice. However, you should avoid alcohol in the air, as it further dehydrates your body.

To reduce leg swelling and lower thrombosis risk, Dr. Weiss recommends standing up regularly in the plane. It can also help to move your feet and tense your calf muscles while sitting to stimulate blood circulation.

And if you have problems with pressure balance in your ears or sinuses, the doctor advises using decongestant nasal drops in advance.

As a healthy person, you can tackle a long-haul flight with these tips effortlessly. It's different if you have certain pre-existing conditions. Those with cardiovascular diseases or serious lung conditions should definitely see a doctor before taking a long-haul flight, advises Dr. Weiss.

'Even wanting to fly a few days after a heart attack requires a thorough examination and stable conditions.' If you've ever had a thrombosis or pulmonary embolism, you should also consult a doctor before the flight. And people with acute sinus infections are also recommended to see a doctor, according to Dr. Weiss.

You should also monitor your body closely during and after a long-haul flight. If you suddenly have breathing pain or shortness of breath, get checked out immediately. The same goes for pain or swelling in a leg, says Dr. Weiss, 'as there might be a thrombosis or pulmonary embolism.' Existing cardiovascular diseases might also deteriorate.

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Travel Reporter