What Causes
Seasickness
A common and often preventable
affliction
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For sure, some of the
passengers on the
Grand Voyager
were probably seasick during their Mediterranean cruise when
it encountered 50' waves and a Force 11 gale in February
this year.
For most of us, though, our concern is how we feel
during more normal weather.
Part 1 of a 2 part series -
part 2 discusses all the
different cures for seasickness. |
They say that, when you're
seasick, you start off worrying that you might die, and then,
after a while, you start to worry that you won't die!
As many of us know from
personal experience, seasickness is a debilitating affliction
that can destroy the otherwise idyllic experience of a sea
journey. Car sickness and motion sickness can similarly
impact on necessary travel.
Understanding the causes of
seasickness enables you to work on preventing the problem.
Next week, we'll focus on how to solve the problem if you still
remain susceptible to this unpleasant and unfortunate illness.
Motion Sickness in General
There are many experiences that can cause what is generally termed motion
sickness. In addition to being at sea on small boats or
large ships, there are plenty of other situations that can bring
on motion sickness - in planes, cars, buses, even trains.
Roller coasters and other fair rides, and even high impact
movies can all trigger motion sickness.
All have common causes and
effects. While we focus this article on seasickness, the
comments relate equally to all other forms of motion sickness.
The Causes of Seasickness
The more we can understand
what makes people seasick, the better we can respond to minimize
these underlying issues, thereby helping prevent seasickness
itself.
Movement
This is probably obvious.
Being at sea on a boat or ship that is moving about a great (or,
for some people, not so great) deal, and accelerative/decelerative
changes in velocity in general, all can cause sea sickness.
A winding road in a car,
air turbulence, or anything else involving the sensation of
changes in speed/direction can induce motion sickness.
Visual disorientation
The other cause is not quite
so obvious. Visual disorientation and strain. Visual
disorientation is when your body senses you are moving, but when
your eyes see no movement.
It can also happen the
opposite way - for example, in an Imax theatre, you might
receive strong visual information suggesting that you're moving,
but your body feels no sense of motion. This can also make
you ill, but fortunately, there's an easy cure for thsi - simply
close your eyes.
Strain happens when you've
having to continually refocus your eyes, for example if trying
to read a book in a car and having the distance and line between
you and the book constantly changing.
Medical explanation
The symptoms of motion
sickness include nausea, vomiting, and dizziness (vertigo).
Early signs are paleness, salivating, yawning, sweating and a
general feeling of discomfort and not feeling well (malaise).
Motion sickness relates to
our sense of balance and equilibrium. Researchers in space and
aeronautical medicine call this sense spatial orientation,
because it tells the brain where the body is in space - what
direction it is pointing, what direction it is moving, and if it
is turning or standing still.
Our sense of balance is
regulated by a complex interaction of the following parts of the
nervous system :
-
The inner ears (also called
the labyrinth) monitor the directions of motion, such as
turning or forward-backward, side-to-side, and up-and- down
motions.
-
The eyes observe where the
body is in space (i.e., upside down, right side up, etc.)
and also the directions of motion.
-
Skin pressure receptors such
as those located in the feet and seat sense what part of the
body is down and touching the ground.
-
Muscle and joint sensory
receptors report what parts of the body are moving.
-
The central nervous system
(the brain and spinal cord) processes all the bits of
information from the four other systems to make some
coordinated sense out of it all.
The symptoms of motion
sickness appear when the central nervous system receives
conflicting messages from the other four systems -- the inner
ear, eyes, skin pressure receptors, and the muscle and joint
sensory receptors.
For example, imagine you are
riding in an airplane during a storm, and the plane is being
tossed about by air turbulence. But your eyes do not detect all
this motion because all you see is the inside of the airplane.
Consequently, your brain receives messages that do not
coordinate with each other. You might become air sick. Or
suppose you are sitting in the back seat of a moving car reading
a book. Your inner ears and skin receptors detect the motion of
your travel, but your eyes see only the pages of your book. You
could become car sick.
Who Gets Seasick
Probably the only person
that really matters is yourself - do you get seasick or not, and
probably, you already know the answer to that!
One study suggested that 14%
of the population gets seasick, but this is a fairly meaningless
number. In an extremely rough sea, way more than 14% of
passengers will get sick. And it shouldn't be taken as a
sign of weakness if you get motion sick - 70% of space
shuttle crew members experience some degree of motion sickness
during the first 3 days of any shuttle flight. You'll even
find that many crew on ships occasionally get sick, too -
including, I must add, me too back when I worked at sea, with
tiresome regularity!
Babies under the age of
about two seem immune from seasickness. Children are more
susceptible than adults, and the older you get, the more
resistant you become (at last - a benefit of growing old!).
The type of motion also has
an impact. The most seasick causing motion is one with
about a five second cycle of repetition. This might be why
some people get sick on big ships (with about a 5 second cycle
of moving from one side to the other and back) but not on small
boats (which move with much quicker motion periods.
Women seem to be more
susceptible to seasickness than men. People of oriental
race seem more susceptible than westerners.
How Likely is it You'll Get
Seasick on a Cruise
Modern cruise ships are
incredibly stable, and their captains do all they can to avoid
rough weather, even to the extent of skipping ports and
rearranging the itinerary if necessary.
The gargantuan size of a
modern cruise ship adds to its stability, and almost every ship
is also fitted with stabilizers to cancel out most of the ship's
movement.
Best of all, most cruise
itineraries have only short periods at sea - often at night,
while you're sleeping - alternating with days in ports.
Most people will find modern
day cruising comfortable and without any associated
sea-sickness.
Getting - and losing - your Sea
Legs
If you're on a multi-day
cruise, you'll find that eventually - usually within 36 - 72
hours - your body adapts and trains itself to ignore the
conflicting messages it is getting. In other words, you
have got your sea legs and are no longer susceptible to
seasickness.
There is an interesting (and
sometimes uncomfortable) opposite to this. You've probably
noticed, when stepping back onto land after being at sea, that
at first it feels as if the land is moving - this being due to
your body automatically anticipating the boat's movement and
having to adjust back to the 'normal' that involves no continual
motion.
Some people find this
'phantom' movement so real that they become seasick again when
they return to shore. This is called 'mal de debarquement'
(as opposed to 'mal de mer' or 'mal d'embarquement' for regular
seasickness).
Minimizing the Causes
Usually the sickness causing
situation is of temporary rather than permanent duration, and so
if you can minimize the impacts on you, there is a better chance
you'll last out until you're back in calm conditions once more,
with both your dignity and your stomach intact.
A stitch in time saves nine
At the first suggestion of
rough weather, take the following precautions so you don't even
start to feel unwell. The more unwell you feel, the more
likely it is that you'll get worse and worse.
Minimizing movement
If you're on a boat, try and
get as close to the boat's center of motion as possible.
This is in the middle of the boat, close to the waterline. If you are at
the bow or stern, you'll experience more motion than amidships.
If you're on the port or starboard railing, you'll again get
more motion than if you're in the center of the boat. And
if you're on the top deck, once again you'll be feeling more
pronounced movements than if you're lower down, close to
sea-level.
In trying to find the
optimum place on a boat, it might be necessary to consider some
compromise so you are also in a place with fresh cool air and a
view outside.
If you're on a plane, the
middle section of the plane, about where the wings are, moves
less than the front, and the back section seems to move most of
all.
And, as just about everyone
knows, the ride is smoother (and the visuals better - see next
point) in the front seat of a car or near the front of a bus.
Minimizing visual
disorientation
You should focus your eyes
at a distant point, preferably the unmoving horizon.
Don't face backwards.
This aggravates the feeling of visual disorientation.
If you're unable to look at
a far-away and hopefully unmoving point of reference, then closing your eyes might be better
than staring at close-by things and adding to the sense of
spatial confusion caused by feeling the sensation of movement
but with no apparent movement visible.
If nothing else, closing
your eyes might help you to relax.
Don't read and don't watch
television.
And also
If you are with other people
and are embarrassed at feeling unwell, try and find somewhere
private where you can suffer stoically and alone. The fear
of being sick is a powerful magnifying factor that can make you
very much more likely to become sick than if you're not so
worried at the thought of possibly being sick.
Some people advocate lying
down, and/or closing your eyes. The primary benefit of
this is that it might help you to relax, and perhaps even to go
to sleep.
Giving yourself a steady
stream of cool fresh air definitely helps, although I have no
idea why that is. Avoid strong smells in general and the
smells of engines and gasoline/diesel in particular.
Try to avoid other travelers
who may also be seasick. There's nothing like the sudden
and powerful
combination of sight, sound, and smell of another passenger
vomiting to bring you past the 'point of no return' as well.
Try to be healthy and well,
so your body has more natural resistance. Don't be
hung over, don't be drinking alcohol, and avoid any food
extremes that might give you an upset stomach, even when on dry
land. You definitely don't want to have a lot of food and
liquid sloshing around in your stomach, so eat and drink in
moderate balanced portions.
Try and be well rested.
Lastly, be prepared, so if
you do need to be sick, you're able to do so with a minimum of
mess. If you use a bag, you should double bag if possible
in case one bag has any holes or comes apart at a seam.
Read more in Part 2
In
Part 2 we discuss the wide variety
of medical and non-medical, scientific and non-scientific cures
that are offered as a remedy for sea-sickness.
Related Articles, etc
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Originally published
11 Mar 2005, last update
21 Jul 2020
You may freely reproduce or distribute this article for noncommercial purposes as long as you give credit to me as original writer.
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