What causes motion sickness

What is Motion Sickness?

Motion sickness, also known as kinetosis, is a common neurological condition that affects millions of people worldwide. It is characterized by a range of unpleasant symptoms, including nausea, vomiting, dizziness, cold sweats, and headaches, triggered by experiencing or anticipating motion. While it can occur in various situations, it is most frequently associated with travel, such as car rides, boat trips, airplane flights, and amusement park rides. The severity of motion sickness can vary greatly from person to person, with some individuals experiencing mild discomfort and others debilitating episodes.

The Science Behind Motion Sickness: Sensory Conflict Theory

The prevailing theory explaining the cause of motion sickness is the sensory conflict theory. This theory posits that motion sickness arises when there is a mismatch between the sensory information received by different parts of your body, particularly between your visual system (eyes) and your vestibular system (inner ear). Our ability to perceive motion and maintain balance relies on a complex interplay of signals from various sensory organs, including the eyes, inner ear, muscles, and joints. The vestibular system, located in the inner ear, is especially vital for detecting acceleration, gravity, and head movements. It sends signals to the brain about our body's position and motion in space.

When you are in motion, your inner ear detects this movement and sends signals to your brain. However, if your visual input doesn't correspond with these signals – for example, when you're inside a car reading a book, your eyes are focused on a stationary object (the book), while your inner ear senses the car's motion – a sensory conflict occurs. Your brain receives contradictory information: your eyes say you're still, but your inner ear says you're moving. This discordance is believed to trigger a response in the brainstem, which is part of the area responsible for regulating nausea and vomiting. The brain interprets this sensory confusion as a potential sign of poisoning or neurotoxin ingestion, a primitive survival mechanism that leads to the 'defense' response of vomiting to expel the perceived toxin.

Factors Influencing Susceptibility

While sensory conflict is the primary cause, several factors can influence an individual's susceptibility to motion sickness:

• Age: Children, particularly those between the ages of 2 and 12, are generally more prone to motion sickness than adults. Infants and toddlers under 2 are rarely affected, and susceptibility often decreases after puberty.
• Genetics: There appears to be a genetic component, as motion sickness can run in families.
• Hormonal Changes: Women are more likely to experience motion sickness, especially during menstruation, pregnancy, or while taking hormonal contraceptives. Hormonal fluctuations can alter the body's sensitivity to motion.
• Medical Conditions: Individuals with migraines, inner ear disorders (like Meniere's disease), or anxiety disorders may have a higher risk of developing motion sickness.
• Previous Experience: A past negative experience with motion sickness can sometimes lead to anticipatory anxiety, which can exacerbate symptoms.
• Type of Motion: The frequency and direction of motion play a role. Low-frequency oscillations (like those on a boat) are often more provocative than high-frequency vibrations. Unexpected or irregular movements can also be significant triggers.
• Environmental Factors: Poor ventilation, strong odors, and enclosed spaces can worsen symptoms for some individuals.

Common Scenarios Triggering Motion Sickness

Motion sickness can be triggered in a variety of situations:

• Car Travel: Reading, looking at a phone, or sitting in the back seat can increase the sensory mismatch.
• Sea Travel: Being below deck, where visual cues of motion are limited, is a common trigger.
• Air Travel: Turbulence can induce symptoms, especially in individuals sensitive to motion.
• Amusement Park Rides: Rides involving spinning, rapid acceleration, and changes in direction are notorious for causing motion sickness.
• Virtual Reality (VR) and Video Games: The disconnect between visual input and physical stillness can lead to 'cybersickness,' a form of motion sickness.

Understanding the Symptoms

The symptoms of motion sickness typically develop gradually but can escalate quickly. Common signs include:

• Nausea
• Vomiting
• Dizziness or vertigo
• Cold sweats
• Headache
• Increased salivation
• Pale skin
• Fatigue or drowsiness
• Loss of appetite

While most cases resolve shortly after the motion stops, severe or prolonged episodes can be debilitating. In rare instances, persistent vomiting can lead to dehydration.

Seeking Relief and Prevention

Fortunately, there are various strategies to prevent or alleviate motion sickness. These include adjusting seating positions (e.g., front seat of a car, facing forward), focusing on the horizon, getting fresh air, avoiding reading or using electronic devices, and consuming bland foods. Over-the-counter medications like antihistamines (e.g., dimenhydrinate, meclizine) and prescription drugs (e.g., scopolamine patches) are also effective. Acupressure bands worn on the wrists can provide relief for some individuals. For frequent travelers, consulting a healthcare professional can help identify the best prevention and treatment options.