If you’ve ever returned from a trip only to immediately get sick, you’re not alone.
Research shows that you're 100x more likely to catch a cold on an airplane than in your everyday life[*], and at the height of the pandemic, air travel was considered a super-spreader of the virus.
While you’re unlikely to catch COVID-19 on your flight from other passengers given the middle-seat and mask policies, you’re still at a greater risk of contracting an illness when you travel due to a suppressed immune system.
Knowledge is power: it’s important to know why you’re so much more likely to get sick when you fly so you can take proactive measures to support your biological systems and immune response.
- Why You Always Get Sick When You Travel
- How Flying Suppresses Your Immune System
- Support Your Body in the Air to Avoid Getting Sick
Here’s Why You Always Get Sick When You Travel
Spending hours in a confined space with hundreds of strangers from around the world, all while breathing in recycled air is a potential breeding ground for illness-causing bacteria and viruses.
But being in close proximity to groups of strangers isn’t unique to traveling, so what makes being on an airplane so different?
The culprit is a compromised immune response due to the bodily impacts of flying.
The increased exposure to pathogens + a weakened immune system = your body unable to fight off infections.
Your immune system is suppressed when you fly due to the very nature of being on an aircraft. Your body is under completely different conditions and needs different support at 30,000 ft than on the ground.
There are a number of changes your body undergoes inflight that contribute to the weakened immunity.
How Flying Suppresses Your Immune System Response
The environmental conditions of aircraft, the very factors that enable a plane to safely fly with passengers on board, suppress your innate immune mechanisms.
Innate immunity is the immune system response that comes from the presence of protective barriers in your body.
These barriers include:
- The skin. Your skin is your body’s largest organ which acts as the barrier between the outer world and your inner environment. Your skin prevents the transmission of most pathogens you’re exposed to.
- The mucous membranes. Mucous membranes create mucous, which helps to filter and trap the pathogens that you breathe in or otherwise enter your body.
- Tears, saliva, and sweat. These bodily secretions contain lysozymes, which are anti-bacterial enzymes produced by the ducts and glands in your body. Lysozymes destroy invasive cells such as bacteria, creating a barrier out of your tears and spit.
- Stomach acid. Any ingested pathogens that aren’t taken care of by the lysozymes in your saliva are attacked again by your stomach acid.
- Immune system cells. Your white blood cells, also called leukocytes, protect against foreign invaders that enter the circulation system.
- Digestive system. The cells, tissues, and organisms present in the digestive tract is responsible for a sizeable portion of your immune response[*], by regulating and defending your body against harmful pathogens.
Below, we’ll go over how each of these innate protective barriers are impacted by the conditions, stressors, and altitudes of an airplane.
#1. Dehydration Kicks off an Immune Response Domino Effect
Cabin air is dryer than the Sahara Desert. Seriously.
You can expect a typical passenger aircraft to have about 12% humidity. The Sahara Desert sees about 25% humidity.
It has to be this way; to support a more comfortable humidity level, the aircraft would have to carry gallons of heavy, expensive water, and would be at risk for excess condensation which can be damaging and corrosive to the parts of the aircraft.
But knowing this isn’t any less harmful to your hydration levels.
When you fly, you likely experience some of the more visible side effects of dehydration. Dry, cracked skin, chapped lips, peeling cuticles, and even nosebleeds are common after spending even a short period of time in the air.
Dehydration can also cause slowed circulation, digestive issues, and fatigue, all of which impair the immune system.
Having dehydrated mucous membranes (especially in the nose) leaves us more vulnerable to airborne viruses as well, as we’ll see below.
#2. Dysregulated Digestive System Reduces Immune Function
If you’ve ever struggled with bloating, gas, or stomach discomfort during or after a flight, you’re not alone.
This is one of the many health impacts of flying that most travelers experience and they’re all symptoms of dysregulation of the digestive system when you fly.
Your digestive system is thrown off for a number of reasons, including:
- Atmospheric pressure. Your body has to adjust to the changing atmospheric pressure on flights which puts added pressure on your digestive system, with gasses expanding and contracting.
- Poor nutrition. Airplane food is not exactly healthy, and airports around the world have a serious problem delivering healthy options to travelers. Most travelers struggle to get adequate amounts of vitamins, minerals and enzymes to ensure proper digestive function.
- Dehydration. Water plays a crucial role in virtually every digestive process and flying causes dehydration, as we learned above.
- Increased pathogen load. Since the digestive system is one of your body’s last lines of defence against harmful bacteria and viruses, the increased amount of pathogens that wouldn’t regularly make it past the initial barriers such as the skin and mucous membranes cause added strain to your digestive tract.
- Impaired circulation. Your circulatory system has a lot of influence over digestive function, which is why exercise is a key component of staying regular. The impaired circulation that happens when you fly only adds fuel to the digestive dysfunction fire.
Given the role that all of these components play in your body’s immune response, it’s no wonder that these disruption to the digestive system impacts your travel immunity.
#3. A Disrupted Circadian Rhythm Disturbs Essential Bodily Functions
Another reason you're so much more likely to get sick when traveling is disrupted sleep.
With travel usually comes jet lag, insomnia, and travel fatigue; all factors that can disrupt the circadian rhythm. Add the fatigue from reduced oxygen levels and jet lag which can reduce your immune response even more, and it’s not just your reaction times that become sluggish.
The circadian rhythm is known as the sleep-wake cycle in the body but it regulates far more than just your body’s internal clock, including your hormonal responses, mental health, and DNA.
Research shows that sleep and the circadian rhythm are highly correlated with immune system function[*], and you don’t have to cross several time zones for your body to feel the impact.
Even an hour time difference can throw your body’s circadian rhythm off and suppress the immune system. This is why instances of illness spike around Daylight Savings Time[*].
#4. Impaired Circulation Slows White Blood Cell Availability
When you fly, your circulation becomes impaired for two reasons:
- You're sitting for prolonged periods of time in unnatural, cramped positions
- Your blood oxygen levels decrease because of the cabin pressure.
Reduced blood oxygen levels are also responsible for the fatigue you experience during your flight.
These two factors cause blood to pool in your body and circulation to slow. Blood circulation is essential for your overall health, as it's responsible for spreading oxygen, nutrients, and those protective immune cells throughout your entire body.
When your circulation is reduced, the white blood cells that attack the foreign cells that have entered your body and blood system are unable to do their jobs effectively.
If you're a flight crew member and think you're safe because you're standing rather than sitting, think again. The same thing can happen when you're standing on your feet for too long.
More serious problems like varicose veins or blood clots can also result.
#5. Reduced Tear & Saliva Production Impairs Lysosomal Protection
Remember those lysosomes we mentioned earlier? Lysosomes are enzymes that destroy bacteria, specifically around the areas of the body that act as openings.
When you fly and notice that you have bloodshot eyes after your flight, this is a side effect of having dry eyes, which is due to dehydration, sleep disruption and also compromised tear production in the eye.
Lysosomes are produced in the glands that make tears, saliva, and other protective fluids in our bodies, and use those fluids as a delivery system for protecting your body against invasive bacteria and viruses.
When your body reduces production of tears and saliva, these protective enzymes aren’t as readily available to act as an immune response.
Support Your Body in the Air to Avoid Getting Sick on Your Next Trip
You just learned exactly why you always get sick when you travel.
All of your body’s protective barriers work together to incite an immune response when faced with harmful pathogens, like the bacteria and viruses that make you sick.
That’s why it’s called an immune system.
And by now, you’re probably seeing how flying not only weakens the functioning of each individual barrier but your immune system as a whole. When one part of a system is failing, the other parts suffer the consequences.
Domestic, international, long haul red-eye or 1-hour direct, these effects don’t discriminate.
The longer the flight, the bigger the impact just by the very fact that you’re spending more time in the air, but don’t get too smug about your short flight. You won’t necessarily catch a break, because your body is still undergoing all of these pressures and changes.
Support your immune system when you travel by ensuring you get the vitamins, minerals, and enzymes you need.
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