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Even if you're a low-maintenance globetrotter, needing only the air that you breathe to feel content and alive, you may find yourself feeling cruddy and in need of some pampering soon after you board an airplane.

Many travelers experience flu-like symptoms on planes that persist through the duration of a flight. Mistakenly, they attribute their temporary unwellness to jet lag, when in fact they may be suffering from dehydration, mild altitude sickness, or the in-the-air variation of "sick building syndrome."

A National Academy of Sciences study in late 2001 raised concerns about cabin air quality. Commissioned by two members of Congress, the study noted that low cabin air pressure and high levels of ozone in cabin air may cause respiratory difficulties, but that there's no way for passengers to complain and that there's no national air-quality standard for commercial aircraft.

"Sick Airplane Syndrome"

If you work in a poorly ventilated, highly populated office space, you're probably familiar with the occupational hazard known as sick building syndrome. Fewer public places are as prone to this condition as an airplane cabin--where strangers are packed, elbow to elbow, with no access to fresh air, for extended periods of time.

Cabin air on almost every domestic aircraft is now recycled, which exacerbates the problem. For years, airlines pumped fresh air into their aircraft cabins from outside. At cruising altitude, air temperature is about -65°F, so the fresh air was pumped through the aircraft's jet engine compressors, which heated it to about 400°F, then chilled it to comfortable temperatures by air conditioners and heat exchangers.

In recent years, however, airline executives discovered that they could curtail fuel expenses and boost profits by mixing 50% fresh air with 50% filtered, recycled cabin air. In fresh air, the oxygen you inhale contains under 1% carbon dioxide. The air you exhale, on the other hand, contains 4% carbon dioxide. When many people share a poorly ventilated, enclosed space for extended periods of time, the carbon dioxide level rises. Carbon dioxide, as you may know if you work in a poorly ventilated office space, is the primary culprit in sick building syndrome.

And although recirculated cabin air is usually passed through air filters that trap allergens, skin flakes, and bacteria, very little new air is being circulated. About 6 to 10 cubic feet per minute of outside air comes into the economy-class cabin--as opposed to the legal minimum of 15 to 20 cubic feet per minute in buildings, and the 50 or more cubic feet per minute the pilots get in the cockpit. This keeps gases, especially carbon dioxide, from being ventilated out of the cabin.

In general, the more time you spend in an enclosed, highly populated, poorly ventilated space like an airplane cabin, the more likely you are to experience headaches, sluggishness, sore throat, coughing, and dry or watery eyes. To boot, the air at high altitudes is dryer than the atmosphere above the Sahara Desert, so you may find your symptoms compounded by dehydration.

Furthermore, evidence suggests that more travelers develop colds in airplane cabins than in other enclosed, highly populated public spaces. This is partly because dehydration diminishes the immune system; but it's also because, as mentioned, few other public spaces keep people in such close quarters for such an extended period of time.

Fortunately, symptoms of poor cabin air tend to vanish soon after you take leave of the offending space. Unfortunately, there's not too much you can do to help yourself. Some suggestions:

  • If your budget allows, fly in first or business class, where fewer people share air space.
  • Don't leave home without your inhaler if you have asthma.
  • Where possible, try to avoid flying with a cold (see "Flying with a Cold," below).
  • If you're on a connecting flight, try to get as much fresh air as you can between connections.
  • Clear your head with a steaming hot shower when you land.
  • Avoid smoke-filled bars when you reach your destination or while you wait for a connecting flight.

Dehydration

While the earth's desert regions have a 20% to 25% humidity level, the cabin of a plane flying at cruising altitude (35,000 ft./10,500m) has a mere 15% humidity content. In this arid environment, your skin evaporates as much as 8 ounces of water per hour. This is why your eyes burn, your lips dry out, your head hurts, and you feel generally sluggish, light-headed, and cranky while you're on a plane.

It's absolutely imperative that you drink lots of water before, during, and after your flight to maintain your body's fluid reserves. Not only will you feel much better, you'll help ward off a host of other maladies. The effects of dehydration compromise the immune system, so you're far more likely to catch the complimentary cold that comes with air travel if you don't drink enough water. Dehydration will also aggravate the symptoms of jet lag.

Even if you don't feel thirsty, drink up. Thirst doesn't necessarily precede the symptoms of dehydration, which can set in without warning. Experts recommend that you drink at least two 8-ounce glasses just before departure and 1 liter for every hour you spend in the air--in addition to the beverages you drink with meals.

Pack a travel-size bottle of skin lotion to replenish moisture in your face and hands during air travel. If you're taking an overnight flight, don't forget to pack a toothbrush, which will help you at least to feel fresher and less dry. Before you prepare to land, visit the lavatory and wash your face and hands, rinsing with cold water.

If you don't want your morning flight to feel like the red-eye, trade your contact lenses for glasses before you board, to keep your eyes from drying out, itching, and turning red. If nothing comes between you and your lenses, you should at least pack some rewetting drops in your carry-on bag.

Pressurization

If you've lived your whole life at sea level, you're likely to feel wobbly on a long-distance flight. When cruising at their maximum level of 40,000 feet (12,000m), commercial aircraft are pressurized to an equivalent of 8,000 feet (2,400m), according to Judith Murawski, an industrial hygienist for the Association of Flight Attendants. That means there's only about three-quarters as much oxygen in the (already somewhat stale) air as there is at sea level.

The pressure level is built into the design of commercial aircraft, according to Murawski. Thickening the air beyond existing levels would require a tougher, heavier skin so the pressure differential doesn't pop the plane like a balloon. A heavier plane means greater fuel expenses. (The Concorde, which flies at 60,000 ft./18,000m and is pressurized to a comfortable 6,000 ft./1,800m), is just that kind of tougher plane--and tickets on the Concorde cost thousands of dollars.)

The thin air in most planes isn't lethal--millions of people around the world live at altitudes of 8,000 feet (2,400m) or greater and are quite healthy. But 8,000 feet (2,400m) is the threshold at which some people begin to develop mild altitude sickness, otherwise known as Acute Mountain Sickness, according to Rick Curtis of Princeton University's Outdoor Action Program. The symptoms of mild Acute Mountain Sickness are headache, dizziness, fatigue, shortness of breath, loss of appetite, nausea, disturbed sleep, and a general feeling of malaise.

And the thin air on board makes flying an anathema to people with heart and lung problems.

There's nothing you can do about pressurization levels on board, and it's ultimately harmless if you're otherwise healthy, but it's also unpleasant.

Pesticides

The cabins of planes traveling to or from certain countries are subject to spraying with pesticides, a controversial practice that has brought complaints from the flight attendants' union and class-action lawsuits filed in 2001 by passengers and flight attendants who say that the bug spray made them sick.

Australia, Fiji, New Zealand, Barbados, Jamaica, and Panama require planes to be sprayed while empty; India, Grenada, Kiribati, Trinidad and Tobago, Madagascar, and Uruguay require actual passengers to be sprayed while on board. The most highly publicized complaints come from passengers and attendants on United Airlines flights from Los Angeles to Sydney, Australia.

Permethrin, one pesticide used in Australia, has ingredients similar to those in lice shampoo. It's banned for use in aircraft cabins in the U.S. because of safety concerns, according to the Association of Flight Attendants.

The World Health Organization and the airlines say that the pesticides are safe. But they haven't been approved by the U.S. Environmental Protection Agency for airline use, and 12 U.S. senators wrote letters to the Bush administration during the summer of 2001 asking that the Department of Transportation force airlines to halt the spraying. In a letter dated June 11, 2001, Transportation Secretary Norman Mineta said the government was "preparing a response."

Flying with a Cold

Next to jet lag, the most ordinary health problem to worry about when you travel by plane is the common cold or flu. During takeoff and landing, even the healthiest travelers experience slight ear discomfort as pressure in the inner ear adapts to rapidly shifting air pressure in the plane cabin. When your mucous membranes are swollen from a cold, the eustachian tube, which connects the sinus cavity to the inner ear, is congested. There's very little room for air to reach the inner ear soon enough to avert severe discomfort--or worse. In the worst instances, you may suffer permanent damage to your eardrums if inner ear pressure can't match cabin pressure at a healthy clip.

If your cold is severe, you should consider postponing your flight. If you simply must fly, however, use a decongestant or nasal spray before takeoff and landing to minimize pressure buildup. Read the label of your decongestant carefully and time your preflight dose so that you'll be able to take another about 1 hour before you're scheduled to land, as sinus and inner-ear pain tend to be most severe during descent.

When you start to feel pressure build in your ears, you can make them pop with a "modified Valsalva maneuver." It's very simple: Pinch your nostrils closed and breathe in deeply. Then breathe out through the nose, as though you were trying to blow your fingers off your nostrils. Blow out in short, firm bursts until you feel your ears "pop." Yawning, drinking liquids, or chewing gum also help to minimize pressure buildup during takeoff and landing.

Antihistamines are even more effective than decongestants, but they will also cause drowsiness. If you're driving yourself from the airport to your destination, it's best to avoid them.

Kids with Colds--It's even more difficult for kids to make their ears pop during takeoff and landing. The eustachian tube is especially narrow in children; the passage is even tighter when mucous membranes are swollen. This can make ascent and descent especially painful--even dangerous--for a child with congested sinuses. If your little one is suffering from a cold or the flu, it's best to keep him grounded until he recuperates, if that's an option. (If you simply must travel with your child as scheduled, give him or her an oral child's decongestant an hour before ascent and descent or administer a spray decongestant before and during takeoff and landing.)

"Economy-Class Syndrome"

Rare but potentially lethal, economy-class syndrome is a result of sitting in cramped conditions for long periods of time. The combination of a sitting position, inertia, and pressure on leg veins reduces blood flow in the lower limbs by two-thirds, according to Dr. Luis Navarro, director of New York's Vein Treatment Center. Stagnant blood in the legs can clot, leading to a condition known as deep vein thrombosis (DVT). If those clots break off and move to the lungs, they can cause a fatal pulmonary embolism like the one that killed British traveler Emma Christofferson in 2000.

Christofferson was flying from Singapore to London--and DVT has most often been reported in people who've taken flights of 8 hours or more. The elderly, pregnant women, women taking hormone therapy or birth control, and people who have recently undergone surgery, have varicose veins, smoke, or have a history of blood clots are most at risk, according to Dr. Navarro.

Economy-class syndrome isn't exclusive to air travelers. Two million Americans suffer from DVT each year, according to Dr. Navarro. In a study published in the medical journal Chest in 1999, French physicians looked at 160 DVT patients. Only about a quarter had taken long trips recently, and of that group, most had been on long car journeys rather than in the air.

The syndrome isn't exclusive to economy class, either. Former Vice President Dan Quayle got DVT in 1994, and his doctors suspected a flight-heavy schedule was the culprit. (Former vice presidents generally don't ride in coach.)

If one of your feet, ankles, or legs swells or aches for longer than 24 hours after you board a plane, seek medical help immediately--from an emergency room, if necessary. The standard treatment for DVT is an injection of Heparin, followed by an oral anticoagulant. This remedy thins the blood and will dissipate the clot--and possibly save your life.

There's fortunately a simple solution to DVT: Move. Get an aisle seat and walk around the cabin every 60 to 90 minutes, to shake up the blood in your legs. Take off your shoes, put your feet up if possible, and don't cross your legs. Drink lots of water to stay hydrated and avoid caffeine and alcohol, which dry you out.

The truly worried, obese, pregnant, or elderly should consider wearing compression stockings, which promote blood flow. They're available at medical supply stores for around $15. Put them on before your flight, while lying in bed, and wear them all day.

You can also stimulate blood flow by doing these leg exercises in your seat:

  • Flex and point. From a sitting position, raise your feet slightly off the floor in front of your seat. Flex your left foot while you point your right. Then switch: point the left and flex the right. Try to perform 10 to 25 repetitions every hour.
  • Round the clock. With your legs still elevated slightly, rotate both your feet outward in a full circle from the ankle--as though they were hands on a clock, one moving clockwise, the other moving counterclockwise. Then switch: rotate them inward. Try to perform 10 to 25 repetitions every hour.
  • Stair master. With your left foot on the floor, raise your right leg a few inches off the floor. Lower it, then raise your left leg to the same height. Repeat this motion, as though you were climbing a flight of very low steps. Try to perform 10 to 25 repetitions every hour.
  • Seated knee lifts. With your left leg on the floor, raise your right knee as close to your body as you can comfortably manage. Return your right foot to the floor and raise your left knee the same way. Return your left foot to the floor. Try to perform 10 to 25 repetitions every hour.
  • Magellan's travel suppliers (tel. 800/962-4943; www.magellans.com) sells an Exercise and Support Cushion ($9.85) that stimulates leg and foot joints and improves circulation when inflated. From a sitting position, you can use your feet to force air through special passages and chambers to relieve the restless sensation you experience when your legs are squeezed in the confines of most airline seats, particularly in coach.

Flying with an Allergy

For the severely allergic, flying can be Russian roulette. Fortunately, the airlines are willing to work with passengers--to some extent. Folks with peanut allergies are protected by a federal regulation requiring three-row, peanut-free "buffer zones" on request. Most airlines will go a bit further and remove peanut-based snacks from entire flights at the request of a passenger with a peanut allergy, although they warn that they can't control what other passengers bring aboard.

If you need to bring an injector or other medical device, make sure you have a note from your doctor and the prescription label from the pharmacy. It's illegal for airport security to take these devices away from you, if they're properly documented.

Peanut-allergic passengers may also want to book business class, where many airlines serve almonds rather than peanuts--and where the air supply won't be contaminated by coach-class snack fumes.

Airlines are less sympathetic to passengers with pet allergies; instead of removing pets from the cabin, they'll remove you from the cabin. Animal-allergic passengers generally have a choice of being reseated away from the pet or taking a different flight at no charge.

Finally, anyone with any sort of food allergy should avoid airline food. You don't know what's in it. Bring your own snacks.