The short answer

Traveling makes you tired because your body is constantly working behind the scenes. Stress keeps your brain on high alert, motion forces your muscles to stabilize, and prolonged sitting reduces circulation. On planes and long car rides, dehydration and lower oxygen levels can also contribute to fatigue.

The long answer

Modern travel mostly involves sitting for long periods—why does it leave you so exhausted?

There are several reasons why traveling makes you feel tired. I included emojis to note which forms of transportation this factor applies to: air travel (✈️), car travel (🚗), train travel (🚆).

✈️ 🚗 🚆 Reason #1: Traveling is stressful, so your brain is on high alert.

From worrying about missing your flight, to remembering to pack everything, to weaving through traffic, traveling is downright stressful. Your brain is on high alert as you're surrounded by new people, navigating new places, and breaking from your normal routine. Being in a state of stress for long periods of time naturally leads you to feeling wiped out when you finally can relax.

✈️ 🚗 🚆 Reason #2: Your body is constantly stabilizing itself.

Sitting in a chair is not the same as sitting in a moving plane, car, or train. While it seems like you're sitting still, your body is constantly making micro-adjustments to keep you upright.

Car travel is especially tiring due to acceleration, braking, and winding roads. You'll also feel more tired on a plane ride that experiences turbulence than one that doesn't. Train travel is less tiring for this reason, simply because it's a smoother journey.

✈️ 🚗 🚆 Reason #3: Sitting for long periods of time reduces circulation which causes fatigue.

Sitting too long without movement slows blood and lymph circulation. These fluids supply oxygen and nutrients to your muscles and joints and take away waste. When circulation is impaired, your body feels more fatigued.

✈️ 🚗 Reason #4: Dehydration leads to fatigue.

Dehydration also contributes to travel fatigue. When your body has less of the fluids it needs to function, it can cause you to feel fatigued.

With air travel, the plane's air circulation system delivers breathable air from the outside to passengers. But at high altitudes, the humidity of that air is only 10-20%, which is far drier than comfortable levels of 30-50% humidity that most people are used to. Over time, breathing in this drier air reduces the moisture within your body, which is why you're advised to stay hydrated on long flights.

Long road trips, especially in summer, can also cause dehydration. When you sit in a car, your body makes contact with the seat which warms your body, increasing sweat and dehydration. Not to mention, you might be intentionally limiting your fluid intake so you have to make fewer restroom stops.

✈️ 🚗 Reason #5: Lower oxygen levels increase fatigue.

Planes are designed to pressurize the cabin so you’re not experiencing the extreme altitudes outside, but the the air pressure inside is still lower than at sea level—roughly equivalent to being at 6,000–8,000 feet (~1,800-2,400 meters). While planes are designed to bring in fresh air, the lower density at altitude means your body has to work harder to absorb and distribute oxygen.

Air always contains about 21% oxygen, but at higher altitudes, those oxygen molecules are more spread out. So with every breath, you’re taking in less oxygen than you would at sea level, making your heart rate increase and contributing to fatigue.

Long car rides can also lower oxygen levels, but there’s an easy fix. If you start to feel drowsy while driving, turn off your air recirculation button.

When turned on, this setting recirculates the air inside the car, making running the A/C more efficient by reflowing the already cooled air. But, it comes at a cost: As you continue to breathe, the level of oxygen decreases and level of carbon dioxide increases. Over time, this can cause you to feel tired. So turn off air recirculation or roll down your windows every so often to get that sweet, sweet oxygen.

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Sources

Kranz, R. (2024, January 2). Symptoms of dehydration: What they are and what to do if you experience them. Harvard Health. https://www.health.harvard.edu/staying-healthy/symptoms-of-dehydration-what-they-are-and-what-to-do-if-you-experience-them

Overdeep, M. (2022, November 4). Here’s What The Air Recirculation Button In Your Car Actually Does. Southern Living. https://www.southernliving.com/travel/car-air-recirculation-button

Pegasus Air Transport Inc. (n.d.). Hypoxia. Pegasus Airlines. https://www.flypgs.com/en/travel-glossary/hypoxia

Staughton, J. (2023, October 19). Why Does Traveling Make You Dehydrated?. ScienceABC. https://www.scienceabc.com/humans/why-does-traveling-make-you-dehydrated.html

Sung, E.-J., Min, B.-C., Kim, S.-C., & Kim, C.-J. (2005). Effects of oxygen concentrations on driver fatigue during simulated driving. Applied Ergonomics, 36(1), 25–31. https://doi.org/10.1016/j.apergo.2004.09.003

Tiwari, A. (2024, January 18). Travel Fatigue: Why Does Traveling Tire You Out?. ScienceABC. https://www.scienceabc.com/humans/travel-fatigue-why-does-traveling-tire-you-out.html

Wichter, Z. (2024, July 19). It’s normal to feel tired on travel days: Why it happens, what you can do about it. USA Today. https://www.usatoday.com/story/travel/columnist/2024/07/17/travel-fatigue-cruising-altitude/74427704007/