Why do we get motion sickness?

By Julian Swallow 2 August 2011
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The act of travelling can be debilitating. For some, motion sickness is enough to turn a trip into a nightmare.

AFTER ALMOST 21 YEARS in the Royal Australian Navy, Lieutenant Commander Jason Gale is intimately acquainted with the pitfalls of his profession, be it deployments on the other side of the world, months spent away from home, or oceanic squalls whipped up by fierce weather.

But for Jason – who is assigned to HMAS Sydney – there is one additional hazard to negotiate: chronic seasickness. While sometimes the effects are fairly minimal, at other times he suffers terribly. On a bad day, Jason endures nausea, grinding migraines, lethargy and, eventually, prodigious bouts of vomiting, which can be brought on by even gentle rolling of the ship.

“I would say my weeks at sea not suffering from seasickness are limited,” he says.

One especially traumatic voyage for Jason was in 2003 – aboard a mine-hunting vessel notorious for bobbing around in rough seas – that left him questioning his will to live. Although the weather was clear and the sea calm, there was no escaping the nausea that dogged him across the South Pacific.

“I was virtually useless when it came to work, spending most of my time in my bed.” Barely able to keep water down, let alone medication, Jason became so dehydrated he was placed on a drip. After attempts to treat him were unsuccessful, Jason finally took matters into his own hands: “I indicated that I was retiring to my cabin to die in peace.” 

Cause of motion sickness

Although his symptoms are unusually severe, Jason is by no means alone. A 2007 US Navy study of 2000 people using a passenger ferry found on average that 60 to 90 per cent of them experienced motion sickness, depending on the conditions.

Whether manifesting as seasickness, carsickness, aviation sickness (or even camel sickness), the disorder that causes the symptoms is collectively classed as ‘motion sickness’. According to Dr David Newman, an aviation medicine specialist at Swinburne University of Technology in Melbourne, it is caused by a conflict between the three primary senses the body uses to interact with its surroundings.

These are:
– the balance organs within the ear’s vestibular system – a set of three semicircular canals arranged at right angles, which allow movement to be detected in three dimensions;
– our eyes, which are the primary source of information about motion;
– and our proprioceptors – pressure sensors found in muscles, tendons and joints that relay the sense of touch.

“Provided they all say the same thing you won’t become unwell,” says David. Motion sickness strikes when they provide conflicting information.

How to treat seasickness 

First described more than 2000 years ago by the Ancient Greek physician Hippocrates, motion sickness has been part of the human experience since at least the time explorers first used simple craft to set forth across the oceans. Indeed, the root of the word nausea is the Greek naos, for ship.

Sailors have always been plagued by motion sickness, but rapid advances in air and rail transportation during the past century mean that worldwide, an estimated 30 per cent of all travellers now regularly have to deal with it when on the move.

“Forty per cent of the student pilots I work with experience aviation sickness when they begin to learn to fly. It can be debilitating at first but they invariably get better,” David says.

This underlines a fundamental point: motion sickness strikes indiscriminately. Paediatrician Dr Linda Gradins, from the Sydney Children’s Hospital, says kids under two years old are highly resistant because they typically travel lying down and don’t rely on visual cues for spatial orientation. Motion sickness occurs most frequently in children between the ages of 10 and 12 – but other than that, there are few patterns as to how it strikes.

Likewise, there is not necessarily any association between types of motion sickness, says David. “Just because you experience carsickness doesn’t mean you’ll necessarily become seasick,” he says. “There is no evidence to suggest one inevitably leads to another.”

However, while our understanding of the reasons people feel motion sickness is incomplete, our knowledge of how to treat it is becoming increasingly sophisticated. In 1939 Robert Blackham, who was a former Honorary Surgeon to the Viceroy of India, wrote in the British Medical Journal that stout had many admirers as a tonic for combating seasickness, “especially among third-class passengers”. For other ranks,  “neat brandy or iced-ginger-ale, or iced water with a few drops of Angostura bitters, are the beverages which have given best results,” he wrote.

Modern-day remedies can include common allergy medications, such as antihistamines, and muscle relaxants. These drugs act to relieve the symptoms, but they are a short-term preventative rather than a cure, says Jessica Vitkovic, a clinical audiologist at the University of Melbourne. Experts are increasingly looking to counter the environmental factors that cause the condition, she says.

“A common way of treating it is to stare at the horizon, because it allows you to maintain your focus on a stable horizontal point, which reduces the conflicting information between the visual and balance senses.”

David’s tips are similar: “Keep your head still – if you move it stimulates the balance organs in your ears; sit in the centre of the ship where it’s [relatively] still; sit over the wing of a plane rather than down the back; lay down.” Ginger is also said to be effective for reducing nausea and vomiting. “I’ve seen no evidence proving it conclusively, but I do know people who swear by it,” he says.

While Jason says he is willing to try most things to overcome his motion sickness, just about the only sure-fire remedy is to allow the body to adjust to the circumstances. “Over time, your body is able to retain a memory of adaptation,” David says. “Motion sickness is normal, and it happens to normal people exposed to abnormal experiences.”

How to beat motion sickness

1. Front and centre: In a car, choose the front passenger seat. In an aeroplane, choose a seat near the wing, where it’s less bumpy. In a boat, stay towards the centre of the vessel. If possible, keep your eyes on the horizon and keep your head still by using a travel pillow.

2. Watch what you eat: Avoid heavy, greasy meals shortly before travel and make sure you keep your fluids up.

3. Dive into the deep end: If you start feeling a little green on a boat, get into the water if you can. This helps prevent confusing signals to the brain.

4. Go old school: Common historic remedies included brandy, ginger ale and bitters. Modern medicinal cures, such as anti-histamine or seasickness tablets, may be less useful than the preventative effect of staring at the horizon.

Source: Australian Geographic, Issue 101 (Jan – Mar, 2011)