Let's see how it all happens. Throwing up often starts with a feeling. You feel sick to your stomach. That feeling is called nausea. You may go pale and feel sweaty. Your mouth can fill with extra spit just before you throw up.

Food goes down a tube called the esophagus, or food pipe. At the bottom is a ring of muscle that works like a door. It lets food into the stomach. Then it squeezes shut so food and acid do not flow back up.

Your body has ways to protect you. That is a big job. Throwing up can get rid of something that might hurt it. The gag reflex helps protect you from choking. Something that goes too far down your throat can set it off.

Riding in a car or a boat can make some people feel dizzy and sick. Your eyes and your inner ears both tell your brain how you are moving. If the messages are different, motion sickness can happen. Looking at the road ahead or the horizon can help, because then your eyes see the same motion your inner ears feel.

A stomach bug, caused by germs, is the most common reason kids throw up. Eating food that has gone bad, called food poisoning, can make you throw up. Kids sometimes throw up after eating too much, because the stomach has been stretched too full.

Now let's talk about that bug. The germs that cause it spread from person to person. Washing your hands with soap and water helps stop them from spreading. Throwing up from a stomach bug usually stops within a day or two.

Here is how the push works. When you throw up, the strong muscles of your belly wall squeeze your stomach. Your diaphragm pushes down hard. Babies often spit up small amounts of milk. That is different from throwing up, which takes strong muscle squeezes.

Most kids throw up sometimes, and it usually does not last long. 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

• nausea: feeling sick
• reflex: quick body reaction
• horizon: distant line
• germs: tiny sickness makers