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Throwing up: It seems to be one of those unwavering rites of childhood, right alongside skinning your knees, and asking “Are we there yet?”

But vomiting, nausea, and stomach upsets aren’t just reserved for kids. Adults deal with these issues too, though the causes may sometimes be different. So what makes kids and adults throw up? Can you prevent vomiting? And, how should you care for someone after they’ve been sick?

Vomiting: A Few Common Causes

There are dozens of conditions that can lead to vomiting or nausea, but there are a few more common causes.

Gastroenteritis: This is what most of us call the stomach flu (though it’s not related to influenza). Gastroenteritis can be caused by bacteria, viruses, and parasites – and often leads to diarrhea and vomiting in adults and kids.

Food allergies and irritations: Although any food can provoke a reaction, several in particular tend to cause most food allergies, including eggs, milk, peanuts, shellfish, soy, tree nuts, wheat, and fish. Nausea, vomiting, and abdominal pain can occur within minutes or hours after ingesting the offending food.

Anxiety and stress: Worries about the new school year, tension about the big game, pressures at work -- all kinds of emotional upsets can lead to nausea and vomiting, though this tends to happen more often with adults or older children.

The flu and other illness: A few other common reasons kids or adults might have nausea or vomiting include ear infections, seasonal flu, swine flu, acid reflux, and reactions to medication.

Eating too much: Many people, especially kids, may eat too much at a holiday dinner or a fair without realizing it, and then throw up.

Food poisoning: Undercooked meats, dairy products, or foods that have been out too long can lead to food poisoning, usually caused by bacteria. Vomiting, diarrhea, abdominal pain, and cramps are other common symptoms of food poisoning.

That’s a lot of reasons to throw up. But “across the board the most common cause for vomiting is probably infection -- gastroenteritis,” says Tanya Altmann MD, a California pediatrician and author of Mommy Calls: Dr. Tanya Answers Parents' Top 101 Questions About Babies and Toddlers.

And you can come across those contagious gastroenteritis germs just about anywhere, from school to daycare, restaurants to movie theaters. Get gastroenteritis, and you can expect to be sick for about a week. But why exactly do we throw up when we don’t feel well?