Why do you get motion sick?

Because your senses disagree about whether you're moving. The balance organs in your inner ear feel the motion of the car, boat or plane, but if your eyes are locked on something still, like a book or phone, they tell your brain you're not moving. Your brain gets two contradictory reports it can't square, and that conflict brings on the nausea, cold sweat and dizziness of motion sickness.

It's the leading explanation for motion sickness. Your brain works out where your body is and how it's moving by combining three streams of information: what you see, what the balance organs in your inner ears detect, and pressure and position signals from your body. Normally they agree. Motion sickness happens when they don't, so the brain receives a mismatch it cannot resolve, and that unresolved conflict triggers the symptoms.

Because it maximises the conflict. When you read, your eyes are fixed on a steady page that moves with the car, so they insist you're sitting perfectly still. Meanwhile your inner ears feel every acceleration, turn and bump of the journey. That's the sharpest possible disagreement between eyes and ears, which is why reading, or looking down at a phone, is one of the fastest ways to bring on carsickness.

Because it lets your senses agree again. When you look out at the road ahead or the distant horizon, your eyes can see the world moving past, which matches what your inner ears are feeling. With vision and balance telling the same story, the conflict shrinks and the nausea eases. That's also why the driver rarely feels sick: they're watching the road and anticipating every move.

Two reasons, both about conflict. First, the driver is looking out at the moving road, so their eyes and inner ears agree. Second, and importantly, the driver controls and anticipates the motion: they know a turn or a stop is coming and their brain can predict the incoming sensations. Passengers get no such warning, so the motion arrives as a surprise their brain has to react to, which makes conflict, and sickness, more likely.

The leading idea is a case of mistaken identity by an ancient survival system. Certain poisons and toxins disrupt the brain and produce exactly this kind of disagreement between the senses. Over evolution, the brain may have learned to treat that sensory confusion as a sign it has eaten something poisonous, and the natural response to poison is to vomit it out. So motion sickness may be your anti-poison defence misfiring on a bumpy road.

Yes, a related one about posture. The postural instability theory argues motion sickness stems not just from mismatched signals but from the brain's struggle to keep the body balanced and stable in an unfamiliar, moving environment. When you can't successfully adjust your posture to the motion, sickness follows. It's often seen as complementary to sensory conflict rather than a rival, adding the body's balancing effort to the picture.

Sensitivity varies a lot between people, and it isn't fully understood. Factors include age (children are often more susceptible, and it can ease in adulthood), genetics, inner-ear sensitivity, and even hormones. Some people habituate with repeated exposure, which is why sailors can get their 'sea legs'. Conditions also matter: a winding, bumpy road causes far more sensory mismatch than a smooth, straight one, so anyone can be pushed over the edge.

It's the same conflict, run in reverse. In VR or a big-screen film, your eyes see a rushing, moving world, but your inner ears feel that you're sitting perfectly still. Now vision says 'moving' and balance says 'stationary', the opposite of carsickness but just as contradictory. The brain gets the same unresolved mismatch and can produce the same nausea, which is why immersive VR and shaky-camera movies leave some people feeling ill.

Most effective tricks work by shrinking the sensory conflict. Sit where you can see the direction of travel, such as the front seat of a car or over the wings of a plane, and keep your eyes on the horizon rather than on a book or phone. Fresh air, keeping your head still against the seat, and taking slow steady breaths all help too. For stronger cases, ginger and over-the-counter travel medicines can reduce symptoms, though it is worth checking with a pharmacist or doctor first.

That lingering rocking sensation on dry land is common after a boat trip and is sometimes called land sickness or, in its persistent form, mal de debarquement. Your brain spent hours adapting to the constant motion of the boat, and it takes a while to readjust to solid ground, so it briefly keeps 'feeling' the sway that is no longer there. For most people it fades within minutes to hours, though rarely it can last much longer and is worth medical advice.

Yes, quite a few do. Dogs are the most familiar example, often drooling or being sick on car journeys, and cats, horses and other animals can be affected as well. Their balance systems work much like ours, so the same sensory mismatch can unsettle them. Interestingly, animals without the same inner-ear balance apparatus, such as those lacking a functioning vestibular system, appear far less prone to it, which supports the sensory basis of the problem.

Motion sickness is especially common in children, roughly from toddler age into the early teens, and often eases in adulthood. The exact reasons aren't fully settled, but a developing balance and sensory system that is still learning to reconcile conflicting signals is thought to play a part. Children are also more likely to be looking down at books, screens or toys in a moving vehicle, which maximises the eye-versus-ear conflict that brings the sickness on.