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Causes of Nausea and Vomiting

Examining the Reasons Why We Toss Our Cookies

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Updated May 19, 2014

Young woman kneeling on floor, holding head in toilet, overhead view
Andy Reynolds/Stone/Getty Images

As miserable as nausea makes 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

Our bodies have evolved to protect themselves. We are supposed to stay alive and do things to ensure that happens every single day. One of the things we've evolved is a protective mechanism against toxic things we might ingest, intentionally or accidentally.

If we eat something that's bad for us, there are several triggers that give us the urge to vomit (nausea). Taste and smell are two of the most powerful. If it smells or tastes nasty, it's probably not good for you.

If you didn't notice the taste or smell, that doesn't mean you're out of the woods yet. If someone else in your vicinity starts hurling up stomach contents, your body wants to join in the fun. The idea is that if everybody in your tribe or hunting party all ate the same nuts and berries then anything that makes your companion toss up lunch should make you do it, too. If it's bad for anyone in the tribe, then your body doesn't want it, either.

That's why when somebody around us starts vomiting, the sights and smells make us feel like joining. (How's that nausea now?)

Oh, but our bodies are not done yet. 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 decide to throw it out. We don't need any poisons in our system that could cause trouble for the noggin.

Armed with an understanding of why we vomit, we can now look at the most common causes of nausea and what, if anything, we can do about it. Although there are several individual reasons for vomiting, they all boil down to three basic things:

  1. Something irritates the brain
  2. Something irritates the gut
  3. Pregnancy

As you may imagine, things irritating the gut are more common than things irritating the brain, so you may be wondering why the brain gets top billing. Well, it's the brain. If you suddenly have nausea or suddenly vomit without first feeling nauseated, it might be something going on inside your melon, and that's not good.

Causes of Nausea Related to the Brain

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 maintanence.

Since there are lots of things that can go wrong with the brain, vomiting is triggered by the brain way more often than it needs to be. An injury to the brain causing swelling inside your skull almost always triggers vomiting, but there is probably no reason why that would help the brain in any way. It's an unintended result of the body thinking any problem with the brain has to be because of something you ate.

However, knowing that brain malfunction will probably result in cookie-tossing reminds us to consider problems with the brain whenever nausea shows up for apparently no reason. There are some things affecting the brain that trigger nausea more often than others:

  • Concussion or traumatic brain injury: This is probably the worst-case scenario. An injury to the brain leads to pressure building up or direct damage to brain tissue.
  • Vertigo or motion sickness: Dizziness related to motion sickness or dizziness related to problems in your inner ear that feel exactly like motion sickness are major causes of nausea. Indeed, this is probably the most treatable cause of nausea. There's a reason that nausea and nautical have the same root word.
  • Too much alcohol: Getting too drunk often results in vomiting. It's how this is supposed to work. You ingest something toxic into your body and the brain gets affected. At first the brain doesn't mind the feeling, but when it gets to be too much or you begin to feel too dizzy, the brain tells your stomach to throw out the leftovers.
  • Carbon monoxide poisoning: Often, folks suffering from carbon monoxide poisoning won't even realize it. They'll be sick with headaches and nausea, feeling much like they have an infection.
  • Heat illness and dehydration: Like I said before, the brain doesn't like to be too hot and needs just the right amount of pressure to work correctly. When it doesn't, it blames the stomach and empties out all the contents.

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

Causes of Nausea Related to the Gut

The mechanism that makes the digestive tract (the gut) want to vomit is a complicated process. The point is that it is supposed to evacuate the stomach when things aren't good for you. Bacteria, viruses and all sorts of toxins can trigger nausea and vomiting from the gut level.

Here are the most common causes of nausea related to the gut:

  • Food poisoning: Not really "poisoning" at all, foodborne illness is usually a bacteria or other bug that's growing on Aunt Jane's famous chicken surprise casserole. There are some common bugs that get us -- salmonella, listeria and E coli are all culprits I'm sure you've heard about -- but they all cause two common symptoms: vomiting and diarrhea.
  • Infections: Besides foodborne illnesses there are other infections, often viruses, that directly attack the gut. Norovirus is one such infamous bug. Often folks will say they have a "stomach flu" but it's not a flu at all.

Tips to Identify What Is Causing Your Nausea

Ultimately, the best way to identify the cause of your upset stomach is to rule out the easiest stuff first. Have you been drinking? Alcohol is a major cause of nausea, so even if you don't think you have a hangover from last night's party, you may still have a little leftover gift. Are you pregnant? The best way to check is with a pregnancy test kit right off the shelf. Are you on a boat? If not, then look for some telltale symptoms:

  • Headache: problems with the brain. If you've recently taken a smack to the melon, a visit to the ER is a good idea. If other people in the house are experiencing the same problem, think carbon monoxide poisoning. Leave the house and call 911. The fire department can check for carbon monoxide in your house.
  • Earache or stuffy sinuses: consider the ear. The inner ear is the way we stay balanced and upright. Sometimes, infection can throw the inner ear's equilibrium out of whack. This might be a case of vertigo.
  • Something you ate: Most of the contaminated food we eat just gets digested like normal without any problem. Once in a while some bad pastrami can throw you for a loop. Food poisoning is more likely in folks who are really old, really young or have weakened immune systems.

Sometimes, nausea is a sign of a really dangerous condition and needs to be evaluated by a doctor. Other times it's just the body's protective instinct at work. There are some things you can try to treat nausea, but in many cases you'll just have to wait it out.

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