Why do we get motion sick?

Your sense of balance relies on the vestibular system in the inner ear, which detects motion and head position, working together with your eyes and the sensors in your muscles and joints. Motion sickness arises when these systems send conflicting information to the brain. In a moving car while reading, for example, your inner ear senses motion but your eyes, fixed on the page, report that you are still. The brain interprets this sensory conflict as a sign of poisoning, since certain toxins disturb balance, and triggers nausea and vomiting as a protective reflex. This mismatch theory explains why looking at the horizon, sitting where you can see movement, or driving yourself often reduces symptoms. Some people are far more susceptible than others, and sensitivity often decreases with age.