A: Motion sickness results from a mismatch between what the brain and body feel and what the eyes see.
The internal receptors in the brain and ears are confused when, for instance, a person is being moved passively in a vehicle, as opposed to moving actively, say, when he is walking.
The same situation can occur when the person is stationary while watching a 3-D show with violent movement.
It can be said that everyone will experience motion sickness if he has a functioning vestibular system in the inner ears, which helps him sense movement and keep his balance.
The other ingredient to motion sickness depends on the strength of external stimuli, usually the motion or perceived motion.
Different people respond differently to different types of motion stimuli.
So some people may have car sickness but not air or sea sickness.
Some people may be at less risk of motion sickness due to habituation, such as seasoned sailors.
So for example, the prevalence of motion sickness ranges from 3 to 60 per cent of passengers on cruise ships.
Some small interesting studies have showed an association between people who are of Chinese ethnicity and increased susceptibility to motion sickness. They experience it more frequently than people of other races and their symptoms are also more severe.
Other studies have shown that pregnant women are more prone to motion sickness too.
On the other hand, older people may be less prone to motion sickness as their vestibular systems may be less sensitive than those of younger people.
Nausea, vomiting and dizziness or giddiness are common when one experiences motion sickness.
These symptoms are usually associated with a decrease in blood flow to the brain and the inner ears.
Stress and tiredness may result in less blood flow to these areas and, thus, they can aggravate or accentuate the onset of the motion sickness.
Most of the pills used to treat motion sickness cause drowsiness.
The other common side effect is dry mouth.
The types of side effects and the extent to which an individual experiences them vary from person to person.
But doctors usually advise a person who has taken such pills not to drive or operate machines unless he has taken similar medication before and was able to perform these activities without problems.
Some pills may not cause drowsiness because they contain caffeine to counter this effect.
However, caffeine itself has its own set of side effects, such as palpitations, which may not be pleasant for some people.
A type of drug to counter motion sickness comes in the form of a patch. Its effect would last up to 72 hours, longer than that of pills. Thus, it would be suitable for longer rides such as boat rides and cruises.
However, it may still cause side effects such as drowsiness and dry mouth.
It would be prudent to discuss with your family doctor before you take medicine for motion sickness, especially if you are on any other types of medication.
The interaction between the different drugs may accentuate the side effects of the motion sickness medication.
It is good practice to eat small meals before long car rides.
Some reports recommend a bland diet that is high in carbohydrates and low in fat. This may reduce symptoms.
Also, avoid spicy, acidic food or food that may be associated with gastritis (stomach inflammation) or gastric acid reflux (the backflow of stomach acid into the food pipe, causing a burning sensation called heartburn).
While riding in a car, besides winding down the window, you could sit in the front passenger seat rather than in the back seat.
Sitting in the back seat triggers more motion issues than sitting in the front passenger seat.
Look far ahead and do not look down or read.
Dr Michael Wong
Senior consultant and head of family medicine at Khoo Teck Puat Hospital
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