There’s a reason why when you get off a long flight, you don’t exactly feel 100%. Beyond grogginess and jet lag, spending hours in a small cabin at 35,000ft, most likely without much room, can take a toll on your body in many ways.

“Sitting for eight hours or more can have serious adverse effects on your health, such as heart and respiratory health, as well as your muscles and joints,” says GP Dr Gill Jenkins.

Here’s how different parts of our bodies are affected…

Heart

“Flying long haul can affect breathing, causing shortness of breath and sometimes chest discomfort. People at highest risk of heart issues on a plane are those who already have cardiovascular disease,” says Jenkins, who is an advisor to Deep Heat, Deep Freeze and Deep Relief.

If you have any heart issues, always check with your doctor if it’s ok for you to fly (and pack any medication needed in your hand luggage).

“Dehydration, changing cabin air pressure and low oxygen concentration – modern aircraft are pressurised to an equivalent altitude of 6000-8000ft, so you are actually breathing in less oxygen”, can all play a part. On top of that, “sitting in a confined space limits chest movements so you don’t breathe as deeply, and increased stress [from flying] can all increase the risk of heart problems”, adds Jenkins.

Deep vein thrombosis (DVT) and blood clots are a particular risk for those without heart disease too, for all the same reasons.

“Blood clots can occur for up to one month after flying, so be alert to symptoms such as swollen or painful legs, especially the calf, and breathing difficulties (clots can occur on the lungs too),” Jenkins says.

To reduce risk, keep well hydrated and don’t drink alcohol during your flight, and stretch and move around as much as possible.

Stomach

A change in humidity can also cause havoc on your stomach.

“Aeroplane cabins have low humidity levels, which can cause dehydration and lead to digestive issues such as constipation and discomfort,” says Dr Simon Theobalds, GP at Pall Mall Medical.

“The change in cabin pressure can also cause gas expansion in the stomach, leading to bloating or discomfort. Prolonged sitting during long flights can contribute to sluggish digestion and constipation.”

The disruptions to your circadian rhythm (body clock) from crossing multiple time zones can affect your digestive system too, leading to irregular bowel movements and appetite changes, he adds. Not to mention that the time zone changes disrupt meal patterns, also “potentially leading to indigestion or stomach discomfort”.

Theobalds recommends staying hydrated and choosing light meals, while also moving around the cabin a lot.

Brain

As the body tries to adjust to different time zones, jet lag can wreak havoc too.

“Changes in sleep patterns caused by time zone differences can affect the quality and quantity of sleep, which can have an impact on cognitive functions and mood,” explains Theobalds. “Low humidity levels can also lead to headaches, dizziness, and cognitive impairment.

“The lower oxygen levels in an airplane cabin may also impact cognitive performance, resulting in symptoms like forgetfulness and difficulty concentrating,” he adds. “For long flights, especially for anxious flyers, stress and anxiety can be triggered, which can affect cognitive functions and overall wellbeing.”

The noise, limited space and crowded conditions can contribute to stress and discomfort as well, “which can influence cognitive performance”.

While these things are usually temporary and reversible, individuals with pre-existing conditions or vulnerabilities may experience more pronounced effects, he says. “It’s crucial to stay hydrated and maintain a healthy sleep schedule.”

Eyes, nose and mouth

These areas can all become very dry on a long-haul flight, due to changes in cabin pressure, altitude and air quality, says Jenkins.

“The circulating air inside an aircraft is very dry, and dehydration from not drinking enough can really exacerbate dry eyes, nose and mouth (and skin and ears).

“Affecting the nasal passages, sinus pain is common on long haul flights, particularly if you already have a cold or other respiratory tract issue, which affect the way the sinuses and nasal passages can equalise pressures following changing cabin pressure – resulting in pain across the eyes, forehead and cheek bones, especially on descent.”

The trick is to get any long-term sinus issues dealt with before flying, but chewing gum, sipping water or yawning before take-off and landing, may help.

“Low humidity can increase tear evaporation and exacerbate dry eye symptoms such as pain, red eye, blurriness, itching, and watery eyes,” she adds. “Because of the dry conditions in the plane cabin, your mouth can also dry out very quickly, causing bacteria to grow on your tongue and bad breath.”

Chewing gum helps stimulate saliva production and relieve a dry mouth, and of course, staying well hydrated.

Skin

Low humidity can also cause your skin to feel dry and tight. “This can lead to flakiness and worsen skin conditions such as eczema or psoriasis,” says Theobalds. “The recirculated air in aeroplanes can be dry and stale, potentially clogging pores and making your skin look dull. This can be especially problematic for those with acne-prone skin.”

Sitting for extended periods can reduce blood circulation, he adds, leading to puffiness around the eyes, contributing to dark circles and generally looking tired.

“At higher altitudes, your exposure to UV rays increases. Although aeroplane windows block most UVB rays, UVA rays can still penetrate, potentially causing skin damage over time,” he says. To combat all this, moisturise your skin, avoid heavy make-up, and use a good-quality SPF.

Limbs and muscles

“Sitting down for several hours on a long-haul flight without much movement may cause muscles to stiffen and could result in joint and back problems and stiffness,” says Jenkins. “During the flight, try to get up, move about and stretch once an hour.  Once you have landed, it’s really important to get your body moving as soon as you can.