Causes of Nausea and Vomiting

As miserable as nausea may make you feel, throwing up has a function. To figure out what’s causing your nausea, it helps to understand why we ever have to vomit in the first place.

The Purpose of Puke

Your body has evolved to protect you. One protective mechanism protects you from toxic things you might ingest.

When you eat something toxic, several triggers give you nausea (the urge to vomit.) Taste and smell are two of the most powerful. If it smells or tastes nasty, your body may reject it as dangerous.

Seeing, smelling, or hearing someone else vomit can make you vomit, too. Your body is programmed this way because if everyone in your group ate the same thing and it made someone sick, you could be next.

But what if nobody else got sick or if you’re all alone? You could still have eaten something bad for you. If it triggers trouble in the brain—especially dizziness—then your gut will throw it out, fearing poison that could cause it trouble.

While vomiting has numerous causes, they all boil down to three basic things:

1. Something irritates the brain
2. Something irritates the gut
3. You're pregnant

Things irritating the gut are more common than things irritating the brain, so why does the brain get top billing?

Well, it’s the brain. If you suddenly have nausea, or you vomit without first feeling nauseated, something bad might be happening inside your cranium, and that’s not good.

Brain-Related Causes of Nausea

Your brain works in a very narrow range of happiness. If it gets too much sugar, it doesn’t work right. If it doesn’t get enough sugar, it doesn’t work right.

It’s too finicky to dine on fat and it needs a certain amount of oxygen. It can’t be too warm or too cold and it can’t be under too much pressure or too little. Basically, brains are high maintenance.

Since lots of things can go wrong with the brain, vomiting is triggered by the brain way more often than it needs to be.

However, knowing that brain malfunction can result in puking reminds us to consider brain problems whenever nausea shows up for no apparent reason. Some brain-affecting things trigger nausea more often than others, including:

• Concussion or traumatic brain injury: An injury to the brain leads to pressure building up or direct damage to brain tissue, which triggers nausea. This always warrants immediate medical care.
• Vertigo or motion sickness: Dizziness related to motion sickness, or inner-ear problems that feel like motion sickness, are major causes of nausea. (There's a reason nausea and nautical have the same root word.)
• Too much alcohol: Getting too drunk often results in vomiting because alcohol is toxic and impacts your brain. It enjoys the early effects, but when they become too strong, it tells your stomach to purge.
• Carbon monoxide poisoning: This cause can be misidentified as an infection because the symptoms of both include headaches and nausea. Carbon monoxide poisoning must be treated with oxygen therapy.
• Heat illness and dehydration: The brain doesn't like to be too hot and needs just the right amount of pressure to work correctly. When conditions are off, it blames the stomach and empties the contents.

Gut-Related Causes of Nausea

Sometimes, nausea and vomiting are triggered by things long before they affect the brain, which is usually better than waiting for a toxic substance to start playing with your higher functions.

The mechanism that makes the digestive tract (the gut) want to vomit is complicated, but essentially, the point is to evacuate the stomach when something in there is dangerous to you.

That's why bacteria, viruses and all sorts of toxins can trigger nausea and vomiting from the gut level. The most common causes of nausea related to the gut are:

• Food poisoning: Not really “poisoning” at all, food-borne illness is usually caused by a bacteria or other bug on something you ate. Common causes are Salmonella, Listeria, and E. coli, which all cause vomiting and diarrhea.
• Infections: Other infections, often viruses, can directly attack the gut. Norovirus is one such infamous bug. Often, folks will say they have “stomach flu,” but it’s not the flu at all. (“Flu” is short for influenza, which is a respiratory illness.)

Identifying the Cause

Ultimately, the best way to identify the cause of your upset stomach is to rule out the easiest stuff first: Have you been drinking? Are you pregnant? Are you on a boat?

If not, then look for some additional telltale symptoms.

• Headaches: A brain problem is most likely. If you’ve hit your head, go to the emergency room. If multiple people in the house have symptoms, think carbon monoxide poisoning. Leave, call 911, and have the fire department check it out.
• Earache or stuffy sinuses: Consider the ear. The inner ear helps you stay balanced and upright. Sometimes, an infection can throw the inner ear’s equilibrium out of whack. This might be a case of vertigo.
• Something you ate: Most contaminated food gets digested without any problem. Once in a while, though, something can throw you for a loop. Food poisoning is more likely if you're really old, really young, or have a weakened immune system.

A Word From Verywell

Sometimes, nausea is a sign of a dangerous condition and needs to be evaluated by a doctor. Other times it’s just the body’s protective instinct at work. You have several options for treating nausea, but in many cases, you just have to wait it out.