What are the health risks of flying and how can we limit their impact?

Flying takes a toll on your body, but with a few practical strategies, you can start your holiday feeling your best

"While many of us are counting down the days until we can jump on a plane and jet off somewhere warm, let’s pause to consider the unique psychological and physiological adaptations that the body undergoes while spending time in the air."

Peak summer holiday season is just around the corner. 

And while many of us are counting down the days until we can jump on a plane and jet off somewhere warm, let’s pause to consider the unique psychological and physiological adaptations that the body undergoes while spending time in the air.

We know the human body is not designed to be at 35,000ft, the typical cruising altitude of a commercial plane. 

The changing air pressure and altered humidity levels can affect the ability to think clearly, cause fluctuations in mood, which some people are more susceptible to than others, making them ‘nervous fliers’. 

Flying can also alter the sensitivity of our taste buds and cause our skin, nose, and mouth to become drier.

However, the more we understand about this sky-high environment, the more we can do to make it a better and less stressful experience for the body.

To begin, despite our inclinations, the latest scientific research suggests it’s best to wait until we touch down before getting stuck into the booze.

A major 2024 study in the journal Thorax revealed that the cabin pressure at cruising altitude exacerbates the impact of in-flight alcohol consumption on the cardiovascular system, lowering blood pressure and increasing heart rate, even in the young and healthy.

Angie Brown, consultant cardiologist and medical director of the Irish Heart Foundation, recommends giving in-flight alcoholic drinks a miss, especially if you have a pre-existing heart condition. 

As well as the findings reported in last year’s study, she says that alcohol can increase the risk of atrial fibrillation, a condition characterised by irregular heart rhythms.

“At high altitudes on flights, sleeping after alcohol can also further lower oxygen levels in the blood and increase heart rates,” says Brown. “This can potentially cause problems for people with heart or lung disease.”

Alcohol is one of the many ways in which our standard flight rituals and the experience of being on a plane can impact our finely tuned biological systems.

Here are more details on how flying impacts your body, along with practical strategies for ensuring you start your holiday in the best possible condition:

Mouth

Bray-based GP Emmett Byrne says it’s common for your mouth to feel dry on a plane because the humidity level in the cabin is generally low, while 50% of the air circulating is taken from the high altitude outside. 

Bray-based GP Emmett Byrne says it’s common for your mouth to feel dry on a plane because the humidity level in the cabin is generally low, while 50% of the air circulating is taken from the high altitude outside. 

“At high altitudes, the air has less moisture in it, so that can give you a dry throat,” he says.

But this is a relatively straightforward fix. “You can combat that by simply being conscious of taking in more water, both before and during the flight,” says Byrne.

Blood vessels

A World Health Organisation study shows that sitting with your knees bent for more than four hours while flying increases your risk of developing a life-threatening blood clot, known as deep vein thrombosis (DVT), by two to threefold.

Byrne says the people who tend to be more at risk of this are those who are overweight, smokers, women taking the oral contraceptive pill, and the over-65s who already have compromised circulation.

Brown points out that susceptibility to DVT can also be heightened by dehydration, which is often exacerbated by alcohol consumption.

“The veins in the legs rely on the calf muscles to help blood get back to the heart,” she says. “With the legs bent, the blood can become more static, and dehydration means the blood is then more likely to clot.”

Byrne recommends, in addition to staying well hydrated, getting up and moving around the plane for five minutes every hour, as long as you’re not asleep. “That will protect you to a certain extent from getting things like clots,” he says.

Ears

As the plane soars higher into the atmosphere, the air pressure reduces, causing the well-known feeling of your ears popping.

“The pressure of the air cabin changes quickly during takeoff and landing, which can affect your ears,” says Byrne. “It creates stress on what’s known as the eustachian tubes, narrow channels which connect the middle ear with the back of the throat, which causes popping.”

As the plane soars higher into the atmosphere, the air pressure reduces, causing the well-known feeling of your ears popping.

However, apart from yawning or swallowing, which may help to mitigate the discomfort, there isn’t much you can do to prevent this.

“That’s something that you just have to deal with,” says Byrne.

Heart

If you experience a cardiac arrest, some studies have suggested that your chances of survival might be higher in an airport or on a plane, thanks to the proximity of trained personnel who can provide CPR, along with readily available resources such as automated defibrillators.

Brown says, while such events are rare, one reason they can occur is due to the impact of high altitudes and reduced oxygen pressure on the heart.

“This can cause hypobaric hypoxia or low oxygen levels, impacting individuals with anaemia or pre-existing cardiac conditions,” she says. “Altitude also increases the heart rate, potentially worsening symptoms in people with heart disease.”

Immune system

No one wants to start their holiday while trying to shake off a bug they’ve picked up from the plane, which can happen as a consequence of being in an enclosed cabin for hours with a large group of people.

“When someone sneezes or coughs, these things are going into the air, and being in closer proximity, you’re at higher risk of catching these things,” says Byrne.

But there’s perhaps a bigger reason why we can end up getting sick on a flight. The immune system is finely calibrated to our body clock, and the dramatic disruption to our normal routine, created by needing to catch a flight, can knock our circadian rhythms out of kilter.

The immune system is finely calibrated to our body clock, and the dramatic disruption to our normal routine, created by needing to catch a flight, can knock our circadian rhythms out of kilter.

“If you think about some of the things you often have to do when going on holiday, you’re either getting up at 3am or 4am to catch a 7am plane, or you’re crossing time zones with a long-haul flight, and all that is breaking your usual circadian rhythm,” says Byrne. 

“This means your immune system takes a hit and you’re a bit more vulnerable than you usually would be.”

However, we can mitigate this by placing our body under less stress. “You don’t have to have a big airport fry-up or drink alcohol before you get on the plane because that will compound the disruption your body’s already experiencing,” says Byrne.

Sleep

One of the most significant changes is how shifting time zones on a long-haul flight can lead to jet lag. 

Flying east, for example, from the US back to Ireland, or from Ireland to Asia, actively speeds up your circadian clock, which can lead to people suffering from so-called sleep inertia for a few days after landing, making it harder for them to wake up.

Flying east from the US back to Ireland, or from Ireland to Asia, actively speeds up your circadian clock, which can lead to people suffering from so-called sleep inertia for a few days after landing, making it harder for them to wake up.

Byrne says that one of the best practical strategies is to try to shift as quickly as possible to the new time zone. For example, if you land late at night, he advises not eating too much on the flight to make it easier to nod off as soon as you arrive at your hotel.

Likewise, if you land mid-afternoon, even after a 12-hour journey, it’s best to try to push through to a normal bedtime.

“The sleep-wake cycle is governed by daylight, and if you adapt to the light by aligning yourself with wakeful and sleeping hours in your new destination as quickly as you can, you’re going to adapt quicker,” says Byrne.

Flight checklist

• Reusable water bottle: Cabins often have low humidity levels, making it vital to stay hydrated.
• Light snacks: Pack granola bars, nuts and fruit to help maintain your energy levels.
• Comfortable clothing: Opt for loose, breathable clothing, and consider layering to adjust to temperature changes.
• Travel pillow: Helpful for long-haul flights when you need to rest and sleep.
• Eye mask and earplugs: Useful for blocking out light and noise while you sleep.
• Small bag: Carry essentials such as mini toiletries, hand sanitiser, antibacterial wipes, and medications.