What is motion sickness

Motion sickness or travel sickness is feeling sick when you travel by car, boat, plane or train. Motion sickness is caused by motion, as sea sickness, train sickness, car sickness, air sickness, or space motion sickness. Motion sickness can cause dizziness, nausea, and vomiting, and although it is not a serious condition, motion sickness can make traveling very unpleasant. Motion sickness can occur in a car, train, airplane, or boat. Anyone can get motion sickness, although children and pregnant women are especially vulnerable.

Moreover, motion is actually not a requirement for motion sickness to occur. Motion sickness can be experienced during activities such as virtual reality rides and playing video games, or by watching movies shot on a shaky camera. The illusion of motion created by the virtual world, combined with the absence of motion detected by the inner ear, results in mixed messages being sent to the brain.

Motion sickness results when the motion you see is different from the motion sensed by your inner ear. Thus, motion sickness occurs when what is seen does not match with what is felt. Mismatched messages about movement that the brain gets from the eyes and inner ears cause motion sickness. For example, when at sea, your eyes view the static horizon or unmoving interior of boat, while your body feels the rolling of the waves. While traveling in a car, the limbs and ears feel little movement, but the eyes perceive scenery passing by. If the motion sensing organs of the inner ear do not work, then motion sickness does not occur. This suggests that the inner ear is critical for the development of motion sickness, and supports the the sensory conflict hypothesis.

The nausea, vomiting, dizziness, and headache of motion sickness arise from sensations that don’t make sense. The eyes of a person reading in a moving car, for example, signal the brain that the person is stationary, because the print doesn’t move. However, receptors in the skin detect bouncing, swaying, starting, and stopping as the inner ear detects movement. The contradiction triggers the symptoms. Similarly, in a passenger of an airplane flying through heavy turbulence, receptors in the skin and inner ear register the chaos outside, but the eyes focus on the immobile seats and surroundings.

Factors influencing motion sickness

Factors that can exacerbate motion sickness include poor ventilation, anxiety and fear. Heavy meals of spicy, greasy food before and during a trip can upset the stomach further, as can alcohol. Pregnancy is also known to increase susceptibility to motion sickness.

There is a clear variation in individual susceptibility which is not well understood. Some research suggests that there may be genetic factors involved and that it may be possible to inherit a predisposition to motion sickness. This has not been definitively confirmed, though the fact that motion sickness is more common in some ethnic groups helps to support this theory. It has been observed that persons of Chinese or Japanese origin are more vulnerable to motion sickness than those of British ancestry.

Motion sickness for kids

Some ways to help combat travel sickness:

• Before you leave, have kids eat a light meal or snack, as motion sickness seems worse on an empty stomach. Provide foods that are easily digested, such as complex carbohydrates, and avoid fatty foods.
• Try to avoid eating during short trips. For longer trips, sip drinks and eat light, small meals and snacks.
• If your child is feeling sick, provide some blander foods, like crackers.
• Encourage kids to look outside the car, rather than inside. They should focus on still objects — not moving ones (like other cars) — or a distant point.
• Keep the window open a little to allow fresh air to circulate.
• Use a headrest to minimize head movement.
• Make frequent stops, if possible, at places like rest stops and parks. And if your child complains of feeling sick and it’s safe to stop, a short walk for some fresh air might help.
• Ask your doctor about medicines to prevent travel sickness.

Motion sickness remedies

Medicines can be used to prevent or treat motion sickness, although many of them have the unwanted side effect of making you sleepy. Talk to your doctor about what is best for you if you think you need medicine for motion sickness. Commonly used medicines are diphenhydramine (Benadryl), dimenhydrinate (Dramamine), and skin patch (scopolamine).

How long does motion sickness last?

Motion sickness lasts as long as the mismatch signals between your outer environment (traveling by car, boat, plane or train) and your inner ear ear balance organs (crista ampullaris) within the Semicricular ducts (see Figures 1, 2 and 4).

Symptoms gradually improve within 15 minutes of the motion stopping, when stomach motility has returned to normal.

How common is motion sickness?

The incidence of motion sickness has been examined in diverse populations. Ungs ¹⁾ found that 64.3% of 238 pilots undergoing flight simulator training reported at least one adverse symptom. Lawther’s ²⁾ study on board passenger ferries also showed similar results with 7% of 20,029 individuals reporting bouts of vomiting. A positive diagnosis of motion sickness was further established for 64% of 45 military parachutists on their first jump by Antuano ³⁾. However, estimates should be understood in the context of the sensory conflict hypothesis. Theoretically, all individuals may suffer from motion sickness symptoms when subject to the necessary stimulus. In this general sense, the incidence and the prevalence of the disorder is dependent on each person’s susceptibility and capacity to adapt to the stimulus as much as it is to the nature of the stimulus itself. Of equal importance is the disabling nature of the disorder when afflicted individuals are unable to perform work‐related tasks, although this aspect of the disorder has been studied less.

Whether or not a person develops motion sickness depends on their individual susceptibility and ability to adapt to movement, as well as the nature and severity of the movement. Almost anyone can experience motion sickness if the motion is severe enough. About half of all astronauts suffer from motion sickness during space travel.

Sex and age also play a role in determining susceptibility. Women are more vulnerable than men, particularly during pregnancy and menstruation. Motion sickness is very common in children older than two years. It peaks at around 9-10 years, then begins to decline into the 20s. This decline may be due to habituation, in which a person stops responding to repetitive stimuli. Infants and children under two years appear to be immune to motion sickness.

People with certain medical conditions are more susceptible to motion sickness. This includes migraine sufferers, those with Meniere’s disease (a disorder of the inner ear), and any patients who have an inner ear disease or vertigo.

Tips for preventing motion sickness

There are things you can do to prevent it or relieve the symptoms.

• In a car or bus, sit in the front (or drive, if possible).
• In an airplane, sit over the wing.
• On a cruise ship, try to get a central cabin.
• Close your eyes or focus them on the horizon.
• Stimulating your other senses can distract you from the motion.
• Aromatherapy (mint or lavender), ginger candy, or other flavored lozenges may help.
• Use visual fixation so that your eyes see the same motion that your body and inner ears feel (e.g. sit in the front seat and look ahead, or watch the distant horizon)
• Choose a seat where motion is felt the least:
  • In a car, sit in the front seat and look at the distant scenery
  • On a boat, sit in the middle cabin, or go up on deck and watch the horizon
  • In an airplane, sit by the window and look outside, or choose a seat over the wings where the motion is minimized.
• Keep your head and body as still as possible
• Lie down on your back
• Sit facing forward and in a reclining position
• Do not read
• Get fresh air by opening a window or going up to the deck of a boat
• Do not drink alcoholic beverages or smoke, as this can increase nausea
• Eat small amounts of low-fat, starchy foods and avoid eating strong-smelling or spicy and greasy foods
• Avoid food and drink on short airplane trips
• On long journeys, eat and drink small amounts, but frequently
• Do not watch or talk to others who are experiencing motion sickness
• Anxiety worsens symptoms. Use relaxation techniques (e.g. abdominal breathing) to occupy your mind
• Soft drinks can help to settle the stomach, and chewing gum or breath mints help prevent saliva from building up in the mouth.

Inner ear anatomy

You rely on the inner ear, an intricate sensory organ, to hear and to maintain balance. The inner ear is a complex system of communicating chambers and tubes called a labyrinth. Each ear has two parts to the labyrinth—the bony (osseus) labyrinth and the membranous labyrinth (Figure 1). The bony labyrinth is a cavity within the temporal bone. The membranous labyrinth is a tube of similar shape that lies within the bony labyrinth. Between the bony and membranous labyrinths is a fluid called perilymph, which is secreted by cells in the wall of the bony labyrinth. The membranous labyrinth contains another fluid, called endolymph.

The parts of the labyrinths include three membranous semicircular ducts within three bony semicircular canals, and a cochlea. The semicircular canals and associated structures provide a sense of equilibrium (balance). The cochlea functions in hearing.

Figure 1. Inner ear anatomy

Figure 2. Parts of the inner ear

Sense of Equilibrium

The sense of equilibrium (balance) is really two senses:

1. Static equilibrium and
2. Dynamic equilibrium—that come from different sensory organs.

The organs of static equilibrium sense the position of the head, maintaining balance, stability and posture when the head and body are still. When the head and body suddenly move or rotate, the organs of dynamic equilibrium detect such motion and aid in maintaining balance.

Static Equilibrium

The organs of static equilibrium are in the vestibule, a bony chamber between the semicircular canals and the cochlea. The membranous labyrinth inside the vestibule consists of two expanded chambers—a utricle and a saccule (see Figure 2).

The saccule and utricle each have a tiny structure called a macula. Maculae have many hair cells, which serve as sensory receptors. The hairs of the hair cells project into a mass of gelatinous material, which has grains of calcium carbonate (otoliths) embedded in it. These particles add weight to the gelatinous structure.

Bending the head forward, backward, or to either side tilts the gelatinous masses of the maculae, and as they sag in response to gravity, the hairs projecting into them bend. This action causes the hair cells to signal the sensory neurons associated with them in a manner similar to that of hair cells associated with hearing. The resulting action potentials are conducted into the central nervous system on the vestibular branch of the vestibulocochlear nerve, informing the brain of the head’s new position. The brain responds by adjusting the pattern of motor impulses to skeletal muscles, which contract or relax to maintain balance (Figure 5).

Figure 3. Inner ear maculae respond to changes in head position

Note: (a) Macula of the utricle with the head in an upright position. (b) Macula of the utricle with the head bent forward.

Dynamic Equilibrium

The organs of dynamic equilibrium are the three semicircular canals in the labyrinth. They detect motion of the head and aid in balancing the head and body during sudden movement. These canals lie at right angles to each other (see Figure 2).

Suspended in the perilymph of the bony portion of each semicircular canal is a membranous semicircular duct that ends in a swelling called an ampulla, which
houses the sensory organs of the semicircular canals. Each of these sensory organs, called a crista ampullaris, contains a number of sensory hair cells and supporting cells. Like the hairs of the maculae, the hair cells of the crista ampullaris extend upward into a dome-shaped, gelatinous mass called the cupula (Figure 4). When the head is stationary, the cupula of the crista ampullaris remains upright. When the head is moving rapidly, the cupula bends opposite the motion of the head, stimulating sensory receptors.

Rapid movement of the head or body stimulates the hair cells of the crista ampullaris (Figure 4). At such times, the semicircular canals move with the head or body, but the fluid inside the membranous ducts remains stationary. Imagine turning rapidly while holding a full glass of water. This action bends the cupula in one or more of the canals in a direction opposite that of the head or body movement, and the hairs embedded in it also bend. The stimulated hair cells signal their associated neurons, which conduct impulses to the brain. The brain interprets these impulses as a movement in a particular direction.

Parts of the cerebellum are particularly important in interpreting impulses from the semicircular canals. Analysis of such information allows the brain to predict the consequences of rapid body movements. By modifying signals to appropriate skeletal muscles, the cerebellum can maintain balance.

Other sensory structures aid in maintaining equilibrium. For example, certain mechanoreceptors (proprioceptors), particularly those associated with the joints of the neck, inform the brain about the position of body parts. In addition, the eyes detect changes in position that result from body movements. Such visual information is so important that even if the organs of equilibrium are damaged, a person may be able to maintain normal balance by keeping the eyes open and moving slowly.

The nausea, vomiting, dizziness, and headache of motion sickness arise from sensations that don’t make sense. The eyes of a person reading in a moving car, for example, signal the brain that the person is stationary, because the print doesn’t move. However, receptors in the skin detect bouncing, swaying, starting, and stopping as the inner ear detects movement. The contradiction triggers the symptoms. Similarly, in a passenger of an airplane flying through heavy turbulence, receptors in the skin and inner ear register the chaos outside, but the eyes focus on the immobile seats and surroundings.

Figure 4. Dynamic inner ear balance organs (crista ampullaris) within the Semicricular ducts

Motion sickness symptoms

The symptoms associated with motion sickness include nausea, vomiting, pallor, cold sweats, hypersalivation, hyperventilation and headaches. These symptoms often occur during travel in vehicles (e.g. cars, trains, airplanes, ships) or when in motion (e.g. fairground rides, swings). Motion is not a requirement for the disorder to manifest. Thus, one can experience the symptoms of motion sickness even when motionless, as when viewing movies shot on a shaky camera or when taking part in ‘virtual reality’ rides in amusement parks. An important aspect of the disorder is the propensity for the symptoms to resolve with continued exposure to stimuli, a characteristic called adaptation or habituation.

The most common symptoms experienced in motion sickness are:

• Nausea;
• Vomiting;
• Dizziness;
• Vertigo;
• Abdominal discomfort;
• Headache;
• Fatigue;
• Pale face and cold sweats;
• Hypersalivation;
• Hyperventilation.

What causes motion sickness

Motion sickness results when the movement you see is different from what your inner ear senses, like going over bumps in a car or moving up and down in a boat. Motion sickness can occur in cars, trains, airplanes, or boats. Anyone can get motion sickness, although children and pregnant women are especially vulnerable.

Motion sickness or travel sickness describes the discomfort felt by individuals caused by repetitive angular and linear acceleration and deceleration. Liquid in the semicircular canals of your inner ear allows you to sense if you’re moving. Your inner ear sends different signals to your brain from those your eyes are seeing. But the brain can get confused if your inner ear senses that you’re moving while your eyes tell the brain you’re not moving. These confusing messages cause you to feel unwell. That may leave you feeling sick, dizzy, or drowsy.

Previous hypotheses about the development of motion sickness held that symptoms were due to either reduced cerebral blood flow or to motion of the viscera prompting stimulation of afferent nerves in abdominal organs ⁴⁾. The most widely held explanation for the cause of motion sickness is described by the sensory conflict hypothesis ⁵⁾. Briefly, the hypothesis postulates that each person has an internal representation of bodily movement. This internal picture is continuously updated by information from sensory receptors such as the eyes, the vestibular system, and mechanoceptors in joints and muscles. Motion sickness develops when repeated and sustained mismatches occur between the information received from the sensory receptors and the expected internal model. It is claimed that adaptation is evidence of the central nervous system’s gradual recognition that conflicting sensory inputs are being received. This leads to appropriate reductions in symptoms.

The symptoms underlying motion sickness are thought to develop as part of the body’s natural defence mechanism. The mixed signals the brain receives lead the brain to conclude that it is hallucinating, and that this hallucination is due to poisoning by a neurotoxin. The brain responds by inducing nausea and vomiting to clear the toxin.

Motion sickness treatment

How you can ease motion sickness yourself

DO

• minimize motion – sit in the front of a car or in the middle of a boat
• look straight ahead at a fixed point, such as the horizon or an object in the distance ahead
• breathe fresh air if possible – for example, by opening a car window
• close your eyes and breathe slowly while focusing on your breathing
• distract children by talking, listening to music or singing songs
• break up long journeys to get some fresh air, drink water or take a walk
• try ginger, which you can take as a tablet, biscuit or tea

DON’T

• read, watch films or use electronic devices
• look at moving objects, such as passing cars or rolling waves
• eat heavy meals, spicy foods or drink alcohol shortly before or during travel
• go on fairground rides if they make you feel unwell

Motion sickness medicine

There are two sub-classes of drugs that can aid in treating and preventing symptoms of motion sickness. These are anticholinergic drugs, and antihistamines. The choice of medication is based on trip duration, any underlying medical conditions, concerns about sedation, and personal preference.

To prevent motion sickness symptoms, oral medications should be taken at least 30-60 minutes before travel to allow adequate absorption time.

You can buy medication from pharmacies to prevent motion sickness, including:

• tablets – dissolvable tablets are available for children
• patches – can be used by adults and children over 10
• acupressure bands – these don’t work for everyone

Your pharmacist will be able to recommend the best treatment for you or your child.

Medications are available by pill are diphenhydramine (Benadryl), dimenhydrinate (Dramamine), and for longer excursions, you can wear motion sickness patch (scopolamine).

Other commonly used drugs include other anticholinergics (e.g. zamifenicin), antihistamines (e.g. meclozine, flunarizine), sympathomimetics and opioids.

Antihistamines

Antihistamines are the most commonly used medication for preventing and treating motion sickness, and work by reducing the stimulation to the inner ear.

Antihistamines include:

• Oral dimenhydrinate (e.g. Calmx, Dramamine, Triptone)
• Diphenhydramine (e.g. Benadryl)
• Promethazine hydrochloride (e.g. Phenergan)
• Meclizine (e.g. Anivert, Bonine, Dramamine II, Meclocot)
• Cyclizine (e.g. Marezine)
• Cinnarizine (e.g. Stugeron)

Dramamine and Bonine are effective for short trips or if symptoms occur intermittently.

Promethazine reduces nausea and may be more effective than other antihistamines, but is the most sedating medication and can impact on psychomotor performance. Meclizine is less sedating and only needs to be taken once a day. Dimenhydrinate has also been shown to impair psychomotor performance compared with placebo, though not to the extent of promethazine.

Only dimenhydrinate and diphenhydramine are recommended for use in children over the age of 2.

Anticholinergics

The most common anticholinergic used is hyoscine, also called scopolamine. Another anticholinergic drug that is used is zamafenacin. Hyoscine works by blocking the cholinergic input from the vestibular organs to the CNS, thereby inhibiting the vomiting impulse activated by motion sickness. Hyoscine is available in several forms, including oral tablets, as an IV, as a topical gel application or as adhesive transdermal patches.

Transdermal patches of hyoscine are recommended for longer trips, as they can be effective for up to three days, while tablets can be taken every six hours. The transdermal patch is applied behind the ear at least 4 hours before departure, and is changed every three days as needed. For maximum effect, the patch should be applied 8 hours before departure. Oral hyoscine is effective for 6-8 hours and can be used for short journeys, or for the interval until an applied patch takes effect. In gel form, hyoscine is most effective when smeared on the arm or neck and covered with a bandage.

Other medications

All motion sickness medications can reduce alertness, and must be used with caution by people who are operating vehicles or heavy machinery. Drinking alcohol or taking other CNS depressants (sleep aids or sedatives) while taking anti-motion sickness drugs increases the side effects of the drugs.

People with low angle glaucoma, gastrointestinal obstruction or urinary retention (e.g. due to prostatic hypertrophy) should avoid these medications. Patients with any cardiovascular, pulmonary, kidney or liver disease should exert caution when taking these medications.

Another drug that is sometimes prescribed is ondansetron (e.g. Zofran), which was originally developed to treat nausea associated with cancer chemotherapy. This appears to be safe for use in children under the age of six.

Some newer medications currently being developed include a class of compounds known as neurokinin-1 (substance P) antagonists. The neurokinins are being investigated for the control of nausea following cancer chemotherapy, as well as nausea related to motion sickness. The first of these drugs available is aprepitant (e.g. Emend).

Behavioral therapy

Desensitization by repeated exposure to the cause of the motion is one of the most effective ways to prevent motion sickness without any side effects. However, this method is specific to the cause. So, if a person becomes desensitized to sea-sickness, his/her vulnerability to car sickness or any other type of motion sickness is not affected.

Behavioral measures such as reducing head movement, gazing at the horizon, lying down, and controlled, regular breathing are all helpful in reducing the severity of symptoms. If there are no windows or it is dark, then closing the eyes or trying to sleep may help. Closing the eyes prevents the conflict that occurs between what is visually perceived and what is sensed by the inner ear. Odors can make motion sickness worse, so try to get some fresh, cool air by opening a window or air vent. It is best to stay in the front seat of a car.

Motion sickness remedies

Ginger root is a highly effective antiemetic without any side effects. The oils contained in ginger appear to relax the intestinal tract as well as mildly depressing the central nervous system. Some of the most effective forms of ginger include the powdered, encapsulated form, ginger tea prepared from sliced ginger root, or candied pieces. Sucking on crystallized ginger or drinking ginger tea can help relieve nausea. All forms of ginger should be taken on an empty stomach.