Flying and Hydration: What Cabin Air Really Does

Atlas was started by a pilot, so cabin air is something we think about. The claims you hear about it, from brain fog to weakened immunity, often go further than the evidence. Here is what is solid.

How dry is the cabin

At cruising altitude the outside air contains almost no moisture. The cabin is supplied with that air, and relative humidity inside commonly runs around 10 to 20 percent, compared with the roughly 30 to 60 percent most people find comfortable indoors. The dryness is most noticeable in your eyes, lips, skin, and nose.

Does dry air dehydrate you

Breathing dry air does increase the water you lose through your breath a little. But studies on whether cabin humidity itself causes meaningful dehydration are few and small, so we would not overstate it either way.

The more dependable reasons people feel dried out on a plane are behavioral: long stretches without drinking because service is infrequent, avoiding the restroom, and choosing alcohol or coffee in place of water.

What about jet lag and brain fog

Jet lag comes from your internal clock being out of sync with local time. Hydration will not fix it, though feeling thirsty and tired at the same time can make everything feel worse. Claims that cabin air suppresses the immune system are not well supported by direct evidence. Crowded, shared spaces are a more plausible reason people catch colds while traveling.

Practical habits

• Bring an empty bottle through security and fill it after. Drinking on your own schedule beats waiting for the cart.
• Drink regularly rather than all at once, and go easy on alcohol.
• Use lip balm, moisturizer, and saline nasal spray for the dryness you can feel.
• On a long-haul flight or when landing into heat, an electrolyte stick in your water bottle is a convenient way to get sodium and potassium without sugar.