Why do some people get motion sick while others don't?

The answer

Motion sickness results from sensory conflict between the vestibular system (inner ear detecting motion), visual system, and proprioception. When your inner ear senses motion but your eyes see a stationary environment (like reading in a car), the brain interprets this mismatch as potential neurotoxin poisoning - since many poisons cause sensory disturbances - and triggers nausea to induce vomiting. This 'poison theory,' proposed by Michel Treisman in 1977, explains why the vomiting center in the brain's area postrema is activated. Approximately 33% of people are highly susceptible, with women 3-5 times more affected than men due to hormonal influences on vestibular sensitivity. Genetic factors account for 57% of susceptibility variance according to a 2015 twin study. Interestingly, people born without functioning vestibular systems never experience motion sickness.