When life gives you lemons, use them to cure motion sickness.
Why on a long road trip, your limbic system loves a citrus scent.
If like me, you were the child who fought for the front seat on any lengthy car journey because it helped keep the sickness at bay, then together we are about to delve into a possible simple solution we so unfortunately missed.
Recently, I have seen a few videos on social media, that have collectively gained millions of views, showing people on road trips and long train journeys smelling and eating lemons to supposedly ‘cure’ their travel sickness. Believe it or not, due to a few shortcuts in your brain’s hardware, this trick might actually work.
I say might, because the brain is a beautifully complex entity and, like this 2018 study explains, no two brains are the same. With this lack of heterogeneity comes the unfortunate disclaimer that the success of this method is not universal.
I, like you might be, was skeptical at first (and due to the lack of solid evidence surrounding brain mechanisms, I still am). However, after pondering this phenomenon for a while and conducting some research, there is some truth behind these videos.
Morning vs Motion Sickness:
There is some evidence to suggest that inhaling lemon scent can combat morning sickness. This provides some grounds for the claims that the same method can be used for motion sickness and nausea in general.
This 2014 study looked at the use of lemon aromatherapy in relation to nausea and vomiting during pregnancy (morning sickness). The trial of 100 women found a statistically significant reduction in symptoms in the test group compared to the control group. If you happen to be pregnant reading this, it might be your sign to put those lemons you have lying around to the test.
So what is motion sickness?
Motion sickness happens when your senses are in conflict. When signals from the body, inner ear and eyes don’t align, physical symptoms such as dizziness and nausea can arise.
When you are riding in a car, or on a plane or boat, the inner ear senses rolling motions that your eyes cannot see, and your body feels forward momentum while your eyes are fixed on a phone screen. And, if like me you felt a little queasy just reading that sentence, its easy to see how your brain can quickly become disturbed.
Get to know your nose:
So if we are to cure our motion sickness by smelling a lemon, we first need to understand how we pick up that scent and how it is translated to the brain.
Our noses are responsible for more than you realise, but often only get as much as a passing glance in the mirror. In fact, our brains make a conscious effort to filter the nose out of your visual field! Noses need to start getting more than a whiffs recognition!
When you breathe in, air fills your nasal cavities which sit above the bone that forms the roof of your mouth, one for each nostril. Each curves down to meet the back of the throat.
As an aside, this is a key part of your anatomy responsible for the tight relationship of olfaction (smell) and taste. It is why when you have a blocked nose, your food tastes somewhat bland. Up to 80% of what you taste is distinguished by smell, so next time you’re enjoying a nice dinner, or your favourite breakfast, you’ve got your nose to thank (mostly).
Returning to the nasal cavity. The lining of these odour-loving hollows (known as epithelium) contains millions of olfactory receptor cells. The ends of these receptors that protrude into the nasal cavity split into finger like projections called cilia.
When odour molecules waft through the cavity, they bind to the cilia to produce a signal that is relayed by the olfactory receptor cell to the connected olfactory nerves.
You can picture this by looking at your arm, imagining that your forearm is the body of the olfactory receptor, and your open hand is the cilia, searching the nasal cavity for odour molecules. When your cilia bind to an odour molecule, it is analogous to you catching a fast moving tennis ball, which sends a vibration up your arm (the generated signal).
The olfactory nerves relay this signal from the odour capture to the olfactory bulbs, you have two, one above each nasal cavity. They are the HQs of olfaction, relaying the sensory signals they receive to many parts of the brain. One collection of structures fed by the olfactory system is the limbic system.
Limbering up:
The limbic system is a collection of many brain structures mainly responsible for regulating emotion and memory (a cool fact on this later).
The close relation of the olfactory bulbs to the limbic system acts like a shortcut in your brain hardware. This means that the signals from the scent you are smelling are able to stimulate the limbic system, a more in-depth mechanism is brought together nicely in this 2022 study. And here in lies one way that lemons could help motion sickness.
The limbic system has an auxiliary role in regulating nausea. The stimulation of the limbic system by the olfactory pathway we have learnt is able to modulate the physiological response to nauseating stimuli and relieve nausea.
Now, this is an incredibly general mechanism which, as a scientist, I find very frustrating. Let me tell you, I was bogged down in research papers for hours looking into this and does appear that there is some truth to this loose theory. This article in the ‘Neuromodulation’ Journal reports that vagal nerve stimulation (a nerve with direct and indirect connection to the limbic circuit as this 2014 study explains) can modulate signals in the brain to change the perception of nauseating stimuli. But, other research such as this 2014 study found no significant reduction in nausea induced motion sickness when inhaling a lemon scent.
If there is one thing to know about the brain, it is that we actually know very little. The “why?” very much still remains, a grey area.
So, we can take this shortcut in our brains to potentially reduce nausea, but lemon scent can also hit the over ride button. The signals generated by the inhalation of potent citrusy aromas can over write the code for nauseating stimuli in the brain. This acts as a small sensory distraction from the nausea and can reduce symptoms.
This is concurrent to something called counter-stimulation. This involves distracting the brain from one stimuli using another. An example of this is rubbing a fresh bruise, your brain focuses on the signals from pressure receptors rather than the pain.
This study reported that all test subjects reported a reduction in pain when their attention was focused on the counter-stimulation stimulus. Therefore, the same idea can be applied to the potent lemon scents stimulating the limbic system and overriding the nauseating stimuli it is also receiving.
So we have seen how sniffing a lemon can indeed reduce nausea symptoms in some people, but what about eating or sucking on a lemon?
Lemon juice contains citric acid, which was shown in this 2021 study to promote digestion peristalsis (the wave like contractions your gut performs to digest food). This small 2022 study also found that citric acid boosted gastric secretions which aids in the digestion of food.
Both of these outcomes would subsequently aid in increasing gastric emptying which can relieve nausea symptoms. This 2022 study found that lemon juice consumption did indeed boost gastric emptying by 1.5x.
So using lemons to reduce nausea can and does work for some people, but the exact mechanisms need further investigation to be fully defined.
Now, to my promised cool fact to wrap up.
One of the most fascinating characteristics of the brain is that it can perform a phenomenon known as associative learning.
We have already established the close connection of the olfactory and limbic systems. The limbic system plays a major role in the regulation of long term memory and emotions, and it can actually connect the scents you inhale, which are relayed to it by the olfactory system, to memories and emotions as this 2013 review evidences.
This is why the smell of freshly baked cookies might trigger memories of your childhood, or the scents of perfumes or laundry detergents of your loved ones can prompt an emotional response.
In the case of lemons and motion sickness, if this technique works for you, your brain can begin to associate the relief of nausea with the citrus aromas. So, the chances are next time you smell lemon, the brain will produce a conditioned response to reduce nausea.
There are many applications of the use of lemons outside of motion sickness. Up to 40% of women use lemon aromatherapy to combat morning sickness in pregnancy. The same technique is recommended to chemotherapy patients to ease the nausea caused by their treatment. This 2023 study showed improved nausea symptoms using peppermint-lemon aromatherapy for children aged 2–12 who were receiving chemotherapy. Lemon aromatherapy is also used to manage post-operative nausea, the results of this 2023 study show a statistically significant reduction in post-operative nausea and in the frequency of anti-emetic (anti-nausea) drug use in patients using lemon aromatherapy intervention.
With these many applications and nausea being an extremely common symptom, you would think that lemons would be a rarity! However, as mentioned at the beginning, brains are like fingerprints, no two are the same.
So, the efficacy of using lemons to treat motion sickness and nausea is debatable. But, if it works for you, I hope you remember your lemon next time you hit the road!
Please leave your thoughts…
