What causes Motion Sickness?

The exact causes of motion sickness (also known medically as kinetosis) are not fully understood. However, experts broadly agree that motion sickness occurs when the brain receives conflicting messages from the various parts of the body that sense and respond to movement.

For example, below decks on a ship the balance receptors in your inner ear may sense a lot of movement, while your eyes don't register any movement at all. Similarly, while reading in a car or bus, your eyes are focused on the unmoving page, while your body registers the movements of the vehicle.

Conversely, motion sickness can also be triggered by the eyes seeing movements, but the body feeling nothing (for example with simulators, 3D movies and IMAX shows).

This sensory confusion disorientates the brain, which doesn't know how to respond, and triggers dizziness. This in turn activates the brain's 'vomiting control center', resulting in nausea and - ultimately - active vomiting.

Why does motion sickness trigger vomiting?

Why sensory disorientation should cause vomiting is not really understood. But I recently came across the fascinating suggestion that it may be because the brain interprets the sensory confusion as hallucinations resulting from poisonous food. The brain then causes the body to vomit the toxins out.

If true, this would be an example of a mechanism that was probably crucial to our distant hunter-gatherer ancestors, but is rather less useful to today's travelers!

Some researchers suggest that low frequency sounds may also play a part in causing motion sickness. They argue that the sound, as well as the vibrations, of vehicle engines and the swell of the sea may disorientate our bodies and trigger nausea. It seems to be a controversial theory, however, as other experts discount it completely.

Other motion sickness triggers

A number of other factors are likely to trigger motion sickness, or make the symptoms worse:
  • Traveling when tired. Do try to get a good night's sleep before traveling!
  • Eating a heavy meal, or greasy or spicy food, before or during a journey.
  • Dehydration. This is a major trigger for many people. Make sure that you are well hydrated before you start your journey, and keep a bottle of water with you and sip from it regularly.
  • Alcohol, tobacco and drugs. Despite old sailing tales, none of these are your friend if motion sickness is likely. It's also wise to abstain the evening before a trip - suffering from motion sickness and a hangover simultaneously is probably one of the worst things you can experience!
  • Feeling cold. Always keep a jacket or travel blanket with you.
  • Strong scents and smells. Obviously vehicle fumes and strongly unpleasant smells are going to make you feel worse, but even pleasant smells, such as perfume, can make you feel ill while traveling.
  • Being near someone who is already feeling motion sick. This can cause a 'chain reaction', with everyone around the sick person starting to feel queasy too.
For more on avoiding these triggers, and what else you can do to prevent motion sickness in all its forms, see Behavior.

The psychological aspect

Motion sickness is undoubtedly a real physical condition (as anyone who has ever suffered from it will confirm!), however it also has a strong psychological aspect. Anxiety, fear and negative associations can make people travel sick while a plane is still on the runway, or the boat still in port. In extreme cases, people have been known to get sick at just the thought of a journey, or from looking at a photo of a ship in rough seas. On the other hand, you may find that positive thinking goes a long way towards preventing severe motion sickness.


Christine on September 25, 2015:
My experience supports the theory that low frequency is a factor. I have crossed the English Channel on a huge ferry when the sea was 'like a mill pond'. I had taken medication and was 'ok', but I could feel discomfort increase when I went to areas with greater engine resonance. This was my first observation.
I've also noticed on airplanes that I am fine forward of the wing, ok over it, and feel worse as I walk towards the back. The jet engines buffet the sides and affect the low frequency movements. There is obviously no change to the view! My absolutely worst ever flights were when I was well back in the tail.
Eileene on August 2, 2016:
I have sailed several long passages at sea over time since 1985, and had MdDS when going ashore but it has always gone away after a short time when I went ashore. For the past 14 years I have lived full time aboard a boat, with short daily walks ashore most days. I lived aboard a different boat for about 10 years. I did go ashore and walk almost daily. I was fine. Since I moved ashore a month ago, it's not been good! I meet the symptoms of MdDS. I have been to see doctors but so far they have not diagnosed MdDS. I thought to internet search land sickness and found this site. Thanks! Now... to step 2.
jim on October 9, 2016:
For the last 10 months I have experienced mild to severe symptoms of motion sickness between 2 and 4 am. I go to bed about 10:30 P.M. If I take promethazine before I go to bed I am ok. Any help, like exercises, or other comments would be appreciated. Thank you.
AlleyCat on October 20, 2016:
I get nauseated from using vibrating massagers around my back or neck area. Can't do it. Also I get nauseated if I am sitting in a car that has a strong bass system vibrating through the seat.
Lulu on March 30, 2017:
My son had never been properly sick in his life until a month ago when he had a temperature at home. He found the whole experience so surprisingly horrible that he now fears it and has suddenly started feeling sick in the car at the age of 9 when it's never been a problem before. Should I use travel pills for a short while to quickly break the cycle psychologically or will he just end up depending on them?
JennyT on October 13, 2018:
Low frequency seems to be my problem - sea calm as anything but the rumblings from the engine makes my stomach churn like a washing machine! Eventually ends up with me being sick, having to lie down and not able to eat for about 24 hours. (Not great on 24 hour ferry trip. Long time of feeling not great.) Used to be okay on ferries but not now!
sgroclkc on February 23, 2021:
Different causes will generate different results. Motion sickness is caused by in-situ rotating motion, 3D visual movement, and low-frequency noise three main causes, with completely different symptoms. The corresponding in-situ rotating motions may cause symptoms of dizziness, 3D visual movement may cause mild dizziness, and low-frequency noise may cause nausea, vomiting, and drowsiness. That is to say rumbling low frequency noise may cause carsickness, seasickness, and airsickness.
Aircon Noise Victim on March 25, 2022:
Yes, it is true that low frequency noise can cause motion sickness. Neighbor's Actron air conditioner emits low frequency noise and we are unable to sleep in our bedrooms because it causes headache, pressure to ear/head and motion sickness. Why council does not recognize low frequency noise? Why do they only measure Decibel A?
Rebecca on January 27, 2023:
"Some researchers suggest that low frequency sounds may also play a part in causing motion sickness. They argue that the sound, as well as the vibrations, of vehicle engines and the swell of the sea may disorientate our bodies and trigger nausea."

This is true in my case. I've always been very sensitive to certain sounds and vibrations. It'll make me slightly dizzy and even sick to my stomach. Anytime there's a vehicle, such as a big truck making the ground vibrate, or even the vibrations coming from a boom box blasting, it makes me nauseous. I always have to sit and lift my feet up and even then, sometimes I can feel it through my seat. It's very annoying. High pitched consistent sounds and sometimes, low pitched, will trigger vertigo most of the time.
sgroclkc on February 8, 2024:
Carsickness is caused by low-frequency noise generated by enclosed carriages (such as cars and buses). Trucks, motorcycles, and tractors do not produce low-frequency noise while driving, and no one will get motion sickness.
sgroclkc on March 27, 2024:
The only reason for motion sickness and seasickness is low-frequency noise. Therefore, only experiments with low-frequency noise can replicate motion sickness. For example, if everyone wears headphones that can generate low-frequency noise, motion sickness can be replicated, while experiments on vestibular function by medical experts can only simulate motion sickness. Wearing headphones that can counteract low-frequency noise can completely prevent motion sickness, and all other methods of avoiding motion sickness are completely ineffective.

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