Many a families’ summer vacations mean piling into the car and heading towards the highway. At times these trips are marred by frequent nausea and vomiting. This means some passengers have a bout of car sickness or motion sickness.
Carsickness, a variant of motion sickness, happens when the eyes, inner ears and joints get conflicting clues about how fast and in what direction the body is moving, says Chamberlain, a clinical instructor at Lucille Packard Children's Hospital at Stanford in Palo Alto, Calif.
The messages from the inner ear (balance department) conflict with the messages from the eye (vision department) causing the brain to take some measures to remove the conflict. As a natural defense against poisoning, the brain will listen to the inner ear over the eyes because vision problems are an early indication of poisoning.
In other words, if your eyes and ears are telling your brain two different things the brain will believe the ear and assume you have been poisoned and begin to make you feel sick until you vomit. Once you vomit the brain will assume you have removed the poison from your body (thats why you feel pretty good just after a vomit session) and resume normal operation. If you are in a car and are looking out the side window your eyes will continue to send a different message to your brain and soon you will begin to feel sick again.