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What is Nausea or Why Do I Feel Sick to My Stomach?

Unravelling Nausea and its Causes

We’ve all been there—that occasional unsettling sensation where your stomach takes a dive. It’s that feeling of being “sick to your stomach.” This sensation is what we call nausea. But what exactly is it, and why does it make an appearance?

What is nausea?

Nausea in simple terms is defined as an unpleasant feeling that tends to pop up before the possibility of vomiting. It is often thought that nausea always precedes vomiting but that is not the case.1 Believe it or not, there’s a reason behind the body’s response.

So why do we experience these uneasy nauseous feelings that stem from our gut?

It’s actually your body’s way of protecting you.2 When something seems wrong, your body’s defense system kicks in. This may lead to a nauseous feeling, and you might even vomit.

This reaction is like a shield, that prevents harmful toxins from getting into your body.

This is also associated with protection during pregnancies, it can be a safeguard for the baby from foodborne chemicals or toxins that may harm the fetus in its critical growth period.3 While other times your uneasy feeling while taking a long road trip may just be triggered by mixed signals received by the brain!

What can cause nausea?

Nausea isn’t an illness or disease; rather, it often emerges as a symptom linked to a range of underlying causes, including:

  • Gastrointestinal (GI) disorders
  • Infection
  • Food poisoning
  • Medications
  • Pregnancy
  • Motion sickness
  • and more!

GI disorders/Infections

Imagine this: your gastrointestinal (GI) tract or gallbladder faces an unwelcome intrusion, and the aftermath is far from pleasant. Accompanied by this invasion are symptoms that include not just nausea, but also diarrhea and abdominal pain.4

The culprits behind these unsettling GI symptoms could be viruses, parasites, or even bacteria. These microscopic invaders wreak havoc on the gut, setting off a chain reaction of discomfort.4

Nausea often stands as the body’s distress signal in the face of these GI intruders. It’s a red flag indicating that something’s wrong in the digestive system.

Nausea also often shares the stage with various GI disorders. Conditions like gastro-esophageal reflux disease, peptic ulcer disease, and irritable bowel syndrome can bring nausea along for the ride.4

Food Poisoning

We’ve all encountered the unwelcome guest of food poisoning at some point in our lives, often after a meal from a local take-out spot. The aftermath? A not-so-pleasant day after. Accidentally ingesting certain types of bacteria, like E. coli or salmonella, can set off an unwanted chain of events. 5,6

Surprisingly, that queasy feeling of nausea plays a pivotal role in this defense strategy. It’s the body’s way of saying, “Hello, something’s not right in here!”

While enduring food poisoning might feel like a storm, the good news is that it’s often a passing tempest. Symptoms can range from a few hours to a few days, but with time, the body’s defences usually prevail.


Our bodies are unique, and so are our reactions to the substances we consume. Different drugs can provoke a variety of responses, leading to potential waves of nausea and even vomiting.7

Medications, both prescribed and over-the-counter, have the potential to trigger a queasy sensation. Examples include:

  • Antidepressants
  • Ibuprofen (e.g.: Advil)
  • Chemotherapy medicines
  • opioid based medicines


Pregnancy journeys aren’t identical for every expectant mother. While not every pregnant woman experiences it, some find themselves battling nausea as early as six weeks into pregnancy.6

This common phenomenon, often dubbed “morning sickness,” paints a picture of a queasy feeling accompanied by occasional vomiting. However, it doesn’t necessarily stick to mornings! This queasy sensation can strike anytime throughout the day.

The good news? It’s typically not harmful to your little one.

However, there’s a more severe form known as hyperemesis gravidarum. This is an extreme case of excessive nausea and vomiting during pregnancy. This usually can lead to excessive weight loss and dehydration. At this point it would be important to reach out to the doctor!

Some ways to mitigate morning sickness is to avoid smells that trigger nausea, eat some crackers to settle the nauseous feeling and drink a lot of water!9,10

Motion Sickness

Ever felt queasy while on a car ride, a sea voyage, or even during a flight? Motion sickness can strike, leaving you with that uneasy sensation and sometimes even a bout of vomiting.

But what’s behind this unsettling experience? Let’s dive into the science of motion sickness and explore why our bodies react this way.

Imagine this: you’re engrossed in a book or glued to your laptop screen while riding in a moving car. Suddenly, the queasiness sets in.

Why does this happen? It’s a result of our brain dealing with conflicting signals. Yes, you heard that right—our brain gets puzzled due to mixed signals it receives from different parts of our body.

Our eyes are locked onto that book or screen, sending signals that we’re in a quite stable environment.

On the flip side, our inner ears are tuned to sense balance and movement. They detect the motion of the car or boat, sending a message to the brain that we’re in motion.

The brain receives contradictory information from our eyes and ears—a recipe for confusion. The brain’s response to this mixed messaging is s release of stress hormones. These hormones can lead to that familiar wave of nausea and sometimes even vomiting.

The good news? This uncomfortable sensation usually doesn’t last long. The body adapts and gets used to the motion, and the brain eventually figures out the true situation.

Maintaining hydration and staying patient will definitely help overcome motion sickness.11

Dealing with nausea

There are some easy steps to find relief from nausea:

  • Light foods: Eat simple foods like crackers or plain bread.
  • Ginger: Ginger, in candies or other forms, can help ease nausea.12
  • Stay hydrated: Drink water to keep hydrated.
  • Avoid greasy food: Skip fried and greasy food that could worsen nausea.
  • Manage triggers: Stay away from smells or things that trigger nausea.

Remember, while nausea can be uncomfortable, it’s usually a sign that the body is working to protect itself. If the symptoms are severe or persistent, it’s a good idea to reach out to a doctor for guidance.


1Singh, Prashant, Sonia S. Yoon, and Braden Kuo. “Nausea: a review of pathophysiology and therapeutics.” Therapeutic advances in gastroenterology 9.1 (2016): 98–112.
2Spiller, R. C. “Anorexia, nausea, vomiting, and pain.” Bmj 323.7325 (2001): 1354-1357.
3Koren, Gideon, Svetlana Madjunkova, and Caroline Maltepe. “The protective effects of nausea and vomiting of pregnancy against adverse fetal outcome—a systematic review.” Reproductive toxicology 47 (2014): 77-80.
4Scorza, Keith, et al. “Evaluation of nausea and vomiting.” American family physician 76.1 (2007): 76-84.
5Hebbard, G., and A. Metz. “Nausea and vomiting in adults: a diagnostic approach.” Australian family physician 36.9 (2007).
6Wagner Jr, Al B. “Bacterial Food Poisoning.” Leaflet/Texas Agricultural Extension Service; no. 1540. (1989).
7Garrett, Kitty, et al. “Managing nausea and vomiting: current strategies.” Critical care nurse 23.1 (2003): 31-50.
8Sherman, Paul W., and Samuel M. Flaxman. “Nausea and vomiting of pregnancy in an evolutionary perspective.” American journal of obstetrics and gynecology 186.5 (2002): S190-S197.
9Ismail, Siti Khadijah, and Louise Kenny. “Review on hyperemesis gravidarum.” Best practice & research Clinical gastroenterology 21.5 (2007): 755–769.
10MacGibbon, Kimber. “What Is Hyperemesis Gravidarum?.” An Educational Guide for Patients.
Heer, Martina, and William H. Paloski. “Space motion sickness: incidence, etiology, and countermeasures.” Autonomic Neuroscience 129.1-2 (2006): 77-79.
11Basirat, Zahra, et al. “The effect of ginger biscuit on nausea and vomiting in early pregnancy.” Acta Medica Iranica (2009): 51–56.1

Kabriya Thavaratnam
Kabriya Thavaratnam
Kabriya Thavaratnam is a doctoral candidate at the University of Toronto, affiliated with Krembil Research Institute, University Health Network. Her academic journey includes the completion of a master's degree program at the University of Zurich, where she specialized in rheumatic autoimmune diseases, laying the foundation for her current research in osteoarthritis. Her academic prowess extends beyond the laboratory, as she possesses over five years of experience in scientific writing, abstract publication composition, public speaking at conferences and grant proposal development. In her leisure time she spends time with her dog, enjoys travelling, and watching movies.


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