Vomiting is the other name for throwing up. When you vomit, your stomach pushes what is inside it up and out through your mouth. This can protect you, because your body gets rid of something that might hurt it. Babies often spit up a small amount of milk. That is not the same as throwing up, which takes strong muscle squeezes.

Food has a path through you. It goes down a tube called the esophagus, also known as the food pipe, and ends up in your stomach. A ring of muscle at the bottom of the esophagus acts like a door. It opens for food, then squeezes shut so food and acid stay down. Throwing up sends food back up the same tube.

Let's start with what you feel. Nausea is the name for feeling sick to your stomach, which often happens before you throw up. Just before it happens, your mouth can fill with extra spit, called saliva. Your inner ear has balance parts that sense when you move. They are connected to the part of the brain that controls vomiting.

Some people feel dizzy and sick when they ride in a car or a boat. Your eyes and your inner ears each tell your brain how you are moving. When those messages differ, you can get motion sickness. Keeping your eyes on the road ahead or the horizon can help the car-sick feeling, since your eyes then see what your inner ears feel.

Let's see what the body does next. Deep in your brain, the brainstem helps decide when you throw up. Strong muscles in your belly wall squeeze your stomach, and your diaphragm pushes down hard. Right before vomit comes up, the glottis closes. That is the opening to your windpipe. Your larynx, or voice box, moves up.

Other things can set it off. Kids sometimes throw up after overeating, since the stomach has been stretched too full. Food that has spoiled, a problem called food poisoning, can also make you throw up. A gag reflex guards you against choking. If something slides too far down your throat, it can set that reflex off.

Now let's look at the top cause. For kids it is a stomach bug, which germs cause. Stomach bug germs go from one person to another. Soap and water on your hands can help stop the germs from spreading. Throwing up from a bug like this usually ends within a day or two. Most kids throw up now and then, and it usually does not last long.

Let's end with a few facts about kids. Kids' bodies are more sensitive than grown-ups' bodies, so kids throw up more easily. Here is what to do. If you feel sick, tell a grown-up, like your mom or dad. A grown-up can check on you and get a doctor if you need one.

Words to know

• glottis: windpipe opening
• larynx: voice box
• diaphragm: body part
• reflex: quick reaction
• horizon: distant line

The short version

Throwing up, also called vomiting, is when your stomach pushes what is inside it back up and out of your mouth. It can be your body's way of protecting you by getting rid of something that might hurt it. Most kids throw up sometimes, and it usually does not last long.

Quick facts

• A stomach bug, caused by germs, is the most common reason kids throw up.
• Washing your hands with soap and water helps stop the germs that cause stomach bugs from spreading.
• Throwing up from a stomach bug usually stops within a day or two.
• Kids throw up more easily than grown-ups, because their bodies are more sensitive.