The cause of motion sickness

DEAR DOCTOR K: I've always had motion sickness while traveling. Now I've started to get it at the movies. What causes motion sickness? And what can I do about it?

DEAR READER: Lots of people get dizzy or nauseated, and even vomit, when traveling by boat, airplane, car or bus. And as you've found, even watching a movie can bring on motion sickness - especially the action scene.

Motion sickness occurs when what your eyes see doesn't match what your body is doing. This is called a "neural mismatch," and it usually follows one of two patterns.

The first pattern is when your body experiences motion that your eyes can't see. Imagine being below deck on a boat. Everything in the room looks stationary to your eye, but your body feels the motion of the boat. Your mind expects you to be able to stand perfectly still, but your body's reaction to the actual movement contradicts this expectation.

The other type of neural mismatch occurs when your body is not actually moving, but your eyes tell it that it is. This can happen when you're watching a movie in a widescreen theater. Movies that include footage filmed from a helicopter can be particularly problematic.

Here are some tips that should help with your motion sickness:

• Travel on an empty stomach.

• On an airplane, try to get an aisle seat toward the center of the cabin, where motion is the calmest. The other advantage of an aisle seat is that if you do get sick and want to vomit in relative privacy, not into a bag with other people around you, it's easier to get to the bathroom.

• On a ship, request a lower-level cabin toward the middle of the vessel. There's less motion there.

• Avoid odors such as perfume, smoke or cooking smells. Open a window for fresh air if possible. Turn on the air vent if you're on an airplane. Odors obviously stimulate the sense of smell, and that stimulation somehow makes the brain more vulnerable to developing motion sickness.

• Don't read or watch videos during bumpy spells. If you are very prone to motion sickness, don't read at all while traveling.

• During a bumpy car or boat ride, keep your gaze fixed on something stationary, like the horizon.

• Avoid alcohol. Too much alcohol, of course, can itself cause nausea, vomiting and dizziness. Even small amounts make the brain more likely to experience those sensations.

• Consider an over-the-counter or prescription motion sickness medication. These may be taken by mouth or as a patch worn behind the ear.

I had very bad motion sickness when I was a child. Fortunately, it has been much less of a problem since then. I don't recall ever getting "seasick" watching a movie, although one 3D movie years ago had a scene on a roller coaster. That one made me close my eyes!

Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.