If your summer vacation involves any type of travel, you may find yourself suffering from motion sickness. An estimated 90 percent of Americans will experience the condition at least once in their lives.

Motion sickness occurs when the brain receives conflicting information regarding movement from the eyes, the body and the inner ear. Motion sensors in your joints and tendons help your brain keep track of your body's movement, while a sensitive network of fluid-filled sacs and canals in your inner ear make it possible for you to maintain your balance.

Reading a book in a moving vehicle is a common cause of motion sickness. While the eyes are focused on the unmoving page of the book, the inner ear senses the car's movement, and conflicting information is transmitted to the brain.

Messages from the motion sensors in joints and tendons throughout the body add to the confusion, and the befuddled brain may retaliate by inducing nausea. Although nausea and vomiting are the hallmarks of motion sickness, yawning, sweating, hyperventilating and an urge to urinate may also occur.

Research suggests that there may be a psychological component to the condition. Some unfortunate individuals experience the signs and symptoms of motion sickness when they do nothing more than think about traveling.

If you're susceptible to motion sickness, you can take steps to prevent it when you travel. Strategically choosing your seat in any moving vehicle is essential.

The seat you'll want is the most stable one. If you're traveling by car, this means the driver's seat.

Drivers are much less prone to motion sickness than their passengers. If you must be a passenger, make sure you call shotgun as soon as possible.

If you're planning to go on a cruise, it may be helpful to stay in a cabin in the front or the middle of the ship, or one on the upper deck. If you're flying, make your reservations early and request a seat over the front edge of one of the plane's wings.

If you're traveling by train, your best bet is to choose a forward-facing window seat near the front. Regardless of your mode of transportation, try to sit in a reclined position with your head resting comfortably against a seat back.

Before you set out on your journey, eat a small, low-fat meal, and then snack lightly every couple of hours if you can. Since alcohol and nicotine can contribute to dizziness and an upset stomach, you may want to avoid drinking alcoholic beverages and smoking before and during travel.

Strong scents or unpleasant odors can increase the likelihood that you'll feel queasy, so ask your travel companion to go easy on the cologne. Anxiety tends to make motion sickness worse, so try to relax.

If these preventive measures don't help, you may benefit from an over-the-counter remedy for motion sickness. Most contain antihistamines and work best when taken 30 minutes to an hour before you embark on your trip.

These medications can make you feel drowsy, which may be a desirable side effect, especially if you plan to sleep through your motion-induced misery. If you need to stay alert during your travels, antihistamines may not be the best option.

If your motion sickness is unfazed by over-the-counter agents, your physician may prescribe the drug scopolamine. Available in the form of a patch, it works best when applied behind the ear about eight hours before travel.

The effects of the patch typically last about three days. Potential side effects include dry mouth, blurred vision and difficulty urinating.

If you prefer to fight motion sickness naturally, you can try taking gingerroot capsules, candy or tea. Scientific evidence suggests that gingerroot is a safe and effective remedy for reducing nausea and vomiting associated with motion sickness.

For some folks with the condition, acupressure may be effective. Asking your travel companion to apply pressure to the inside of your wrist may help reduce nausea.

If your travel companion won't cooperate, you can buy specially designed wristbands that will. The bands feature knobs that apply gentle pressure to acupressure points in your wrists, which may help alleviate symptoms of motion sickness.

If all forms of prevention fail, all you can do is prepare yourself for the inevitable. Arm yourself with a supply of sturdy motion sickness bags whenever you travel, and hold on for the ride.

Rallie McAllister, M.D. is a family physician, speaker, and co-founder of www.MommyMDGuides.com, a website featuring child-raising tips from trusted doctors who are also moms. To find out more about Rallie McAllister, M.D., and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate Web page at www.creators.com.