In-flight air is drier than any of the world's deserts. Relative humidity is 20-25% in the Sahara or Arabian deserts, while optimum comfort is around 50% humidity.

In-flight cabin humidities gradually fall on long-distance, high-altitude flights in many cases approaching 1%.

Basically, there's no way to avoid the fact that your body will become dehydrated to some degree as a result of flying long distances in near-zero humidity in commercial jet cabins. So we need to be mindful of our water intake en route, and also remember to drink plenty of pure water for several days after landing.

In-flight dehyration is one of the most serious hazards long-distance flyers face.

SYMPTOMS OF DEHYDRATION ON BOARD

Thirst, scratchy eyes, bloodshot eyes, dry skin, wrinkled skin, backed-up plumbing, and more.  

Without adequate water intake, health and inspiration quickly deteriorate.

TIPS TO AVOID DEHYDRATION

1. Drink at least eight ounces of water every hour en route.

2. Carry your own bottle of drinking water when you fly, to sip on when service is not available (right after takeoff or when the bar carts close prior to landing) and/or when flight attendants are not in your section.

3. En route, ask for bottled or canned water when the bar cart comes by. (Avoid tap water on airplanes. There are no standards for commercial aircraft water tanks, for cleanliness, treatment procedures, nor water quality in cities around the world where commercial jets refill.) 

4. Avoid alcohol and coffee; they have diuretic properties, i.e., they squeeze water out of our cells. 

5. Spritz your face often; use an empty perfume atomizer and refill it from your own drinking water or buy a water spritzer (used for ironing). 

6. For humidified breathing air, cover your nose with a water-saturated cotton handkerchief. (Fold on the diagonal and wrap ends around your ears.) Leave it on as much as possible during the flight. It will also help to block the spread of germs—even tuberculosis.

6. After landing, submerge and soak in water as soon as possible—the ocean, a hot tub, a pool, a bath, whatever is available that you enjoy. Immerse entirely, and especially your head. Bathing when dehydrated helps to replenish moisture right through the pores. Bathing also relaxes the nervous system.

7. Before you fly, apply an edible vegetable oil inside your nostrils to protect the delicate mucous membranes from the abusive dry cabin air. I definitely do not recommend petroleum jelly. Picture this: anything you put in your nose, you are ingesting right into your brain. Try almond oil from the health food store. It smells nice. Jojoba oil is also good and a little thicker. Organic olive oil is now easy to get and it will also do the job. 

FROM READERS

"Thank you for the tips on keeping my nose moist on long flights. While growing up, I had a friend who got frequent nose bleeds, but the only time my nose ever bled was when I was hit in the face with a soccer ball--until I spent 20 hours on a flight that took me from Dallas to Chicago to New York to Buenos Aires, to Santiago, Chile. Somewhere between New York and Buenos Aires my nose started to bleed. Since I never had nose bleeds, I knew it had to be from the dryness of the cabin air. Now I am planning a return trip. Thanks for the tips." -M. Ferrin