Motion Sickness

Definition and epidemiology

Motion sickness, also known as travel sickness, is the set of symptoms such as nausea, sweating, altered arousal and dizziness caused by physical or visual motion. In criteria published in 2021, the Bárány Society defined motion sickness triggered by physical motion separately from visually induced motion sickness (VIMS), triggered by visual motion on screens, in cinemas or in virtual reality. Where symptoms are recurrent, predictable and restrict behaviour, the terms motion sickness disorder and visually induced motion sickness disorder are used (Cha et al., 2021).

Motion sickness is very common. It affects 35-43% of children before puberty and about 25% of young adults; as a frequent problem in adults it is reported by 14% of those under 30 and 7% of those aged 61 or over. The frequency of visually induced motion sickness ranges from 1% to 95% depending on the stimulus and visual content (Cha et al., 2021). In most people this response of a healthy balance system to unfamiliar motion is not regarded as a disease, although susceptibility varies widely between individuals.

Symptoms and signs

The Bárány criteria group symptoms into five domains: gastrointestinal symptoms such as stomach awareness, nausea and vomiting; thermoregulatory disruption such as sweating and feeling hot; changes in arousal such as yawning, drowsiness and apathy; dizziness or vertigo; and headache and eye strain (Cha et al., 2021). Symptoms start during motion, build up with continued exposure and settle within a period after motion ends. Although nausea and vomiting are the best-known symptoms, in some people drowsiness and reduced alertness dominate (sopite syndrome).

Children are resistant until about the age of two; susceptibility peaks at 7-12 years and then declines. In visually induced motion sickness, by contrast, susceptibility appears to rise with age, and older adults report more symptoms (Cha et al., 2021). Virtual reality headsets, video games, wide-screen cinema and looking at screens in a vehicle can cause similar symptoms even without real motion. The spread of automated vehicles and virtual reality has brought renewed attention to motion sickness, which is seen as a problem that could limit public acceptance of these technologies (Keshavarz and Golding, 2022).

Causes and risk factors

The most widely accepted explanation is sensory conflict (neural mismatch) theory: symptoms arise when motion signals from the labyrinths, eyes and body disagree with each other or with the motion the brain expects. A passenger reading in an enclosed cabin has labyrinths that sense motion while the eyes see a stationary page; in virtual reality the eyes see motion while the labyrinths sense none. Mismatch between the semicircular canals and otolith organs, and between the perceived and actual direction of gravity, also form part of the theory (Cha et al., 2021). Postural instability theory proposes instead that symptoms arise because the person has not yet developed strategies to keep their posture stable in a new motion environment, so that instability precedes sickness (Riccio and Stoffregen, 1991). Evolutionary explanations also exist, such as the toxin hypothesis, which sees motion-induced vomiting as a by-product of an ancient defence against poisoning (Cha et al., 2021).

Risk factors include (Cha et al., 2021):

• Age: childhood, especially 7-12 years.
• Female sex: surveys at sea show a female-to-male risk ratio of about 5 to 3 for vomiting (Golding, 2006), although the difference was significant in only half of studies and is linked to hormonal factors.
• Migraine: at least half of people with migraine report susceptibility to motion sickness. In one study the highest susceptibility scores were found in people with migraine and with vestibular migraine, and 75% of those with vestibular migraine reported increased susceptibility after onset (Murdin et al., 2015).
• Heredity: a twin study estimated the heritability of childhood motion sickness at about 70%.
• Vestibular disorders: Ménière’s disease increases susceptibility; in vestibular neuritis the effect depends on compensation.

Bilateral vestibular loss has the opposite effect: people without functioning labyrinths do not develop motion sickness even in the roughest seas (Cha et al., 2021). Patients with bilateral vestibular hypofunction had the lowest susceptibility scores, and none reached moderate nausea within 20 minutes of a rotational stimulus (Murdin et al., 2015). This shows the central role of the labyrinth in motion sickness, although these individuals may still be susceptible to visually induced motion sickness (Golding, 2006).

Audiological and clinical assessment

The diagnosis rests on the clinical history, and most people need no tests. The Bárány Society criteria define two levels (Cha et al., 2021):

Audiological and vestibular assessment comes into play when symptoms cannot be explained by motion or the picture is atypical:

• History and questionnaires: the Motion Sickness Susceptibility Questionnaire (MSSQ) asks about travel experiences in childhood and adulthood; on the short form, scored 0-54, about 90% of people score 0-27 (Cha et al., 2021). The six-item Visually Induced Motion Sickness Susceptibility Questionnaire (VIMSSQ) shows good internal consistency (Cronbach’s alpha 0.84); alone it predicted 34% of individual differences in symptoms provoked by an experimental visual stimulus, and 56% together with the MSSQ, migraine and other factors (Golding et al., 2021).
• Pure-tone audiometry and vestibular tests: no findings are expected in motion sickness. If dizziness occurs without motion, or there is hearing loss, tinnitus or aural fullness, a test battery (pure-tone and speech audiometry, video head impulse test, caloric testing, VEMPs) is used to look for Ménière’s disease, vestibular migraine and other vestibular disorders.
• Care during testing: caloric and rotational testing and optokinetic stimuli can provoke nausea and sweating in susceptible people, who should be warned beforehand.
• Complete lack of susceptibility: in a patient with unsteadiness who has never been travel sick, even on rough journeys, bilateral vestibular loss should be considered.

In the differential diagnosis, symptoms that begin after motion ends and ease with renewed travel suggest mal de débarquement syndrome; dizziness lasting at least three months and worsened by standing, motion and complex visual surroundings suggests Persistent Postural-Perceptual Dizziness (PPPD); and attacks with migraine features suggest vestibular migraine (Cha et al., 2021).

Treatment and audiological rehabilitation

Prevention rests on reducing exposure and mismatch: limiting head movements, sitting in the front of a vehicle and increasing earth-fixed visual cues by looking at the horizon or the road, and avoiding reading or screens while travelling (Cha et al., 2021). Benefits have been reported for music, pleasant smells, breathing exercises and meditation; the evidence for ginger and acupressure is mixed (Cha et al., 2021). Among non-drug methods, habituation is the most effective. Regular, graded exposure to the stimulus reduces symptoms, and military desensitisation programmes report success rates above 85%. Intervals of more than a week between exposures almost prevent habituation (Golding, 2006). Habituation is usually stimulus-specific: someone who has adapted to boats may still become sick on a plane (Cha et al., 2021).

Medication works better when taken before the journey, before symptoms begin (Cha et al., 2021). The choice of drug and dose rests with the doctor, and care is needed in children, older people, pregnancy, and in people with glaucoma or prostate problems. A Cochrane review of 14 randomised trials (1025 participants) found scopolamine more effective than placebo for prevention and more likely to cause dry mouth; no randomised trials were found on treating established symptoms (Spinks and Wasiak, 2011). Antihistamines probably prevent symptoms better than placebo under real travel conditions (moderate-certainty evidence) but may cause more drowsiness; no clear difference from scopolamine was shown (Karrim et al., 2022). Sedating drugs may be unsuitable for people who will be driving.

In people diagnosed with motion sickness disorder whose symptoms restrict work or daily life, graded visual and vestibular exposure can be used within a vestibular rehabilitation programme; clinical studies are limited, however, and a reliable method of prevention has yet to emerge (Keshavarz and Golding, 2022). In patients whose susceptibility is linked to migraine, planning migraine treatment with a doctor may help.

Impact on quality of life and advice

For most people motion sickness only makes journeys harder; for some it leads to avoiding school trips, holidays or business travel, and to difficulty with screen-based work and virtual reality applications. Anxiety before a journey can make symptoms worse. Susceptibility also matters for careers at sea, in aviation and in fields that use virtual reality.

Practical advice: sit in the front of the car or drive yourself if possible; on a boat, stay near the middle and at deck level, and look at the horizon. Do not read or look at screens while travelling, and rest your head against the seat to limit head movements. Avoid heavy meals and alcohol, and keep the cabin well ventilated. With virtual reality and video games, start with short sessions and lengthen them gradually, taking a break if symptoms start. If your child gets travel sick, plan journeys with frequent breaks and ask a doctor before giving any medicine. If symptoms continue after the journey ends, tell your doctor.