Throwing up has a job to do. Vomiting, also called emesis, is a forceful push that sends stomach contents out of the mouth. Sometimes the body needs to get rid of something that might hurt it, and throwing up is one way it protects you. Many people feel better for a while once they have vomited, because the stomach has been emptied of what was bothering it.

Stomach bugs, which germs cause, are the most common reason that kids throw up. Many stomach bugs come from viruses such as norovirus, which spread easily between people. These germs pass from one person to another. When a stomach bug is the cause, the throwing up usually stops in a day or two. Before it starts, you often feel sick to your stomach, and that feeling is called nausea. A person who feels sick to the stomach may turn pale and sweaty.

Germs are one thing to watch, and food is another. Washing your hands with soap and water helps stop the germs that cause stomach bugs from spreading. Food poisoning, which comes from eating food that has gone bad, can also make you throw up. Both of these are about something that gets into the body, and the body answers by pushing it back out. A stomach that has been stretched too full by eating too much can make a kid throw up.

Some causes are not about germs at all. A gag reflex guards you from choking, and something that goes too far down your throat can trigger it. Some people throw up when they feel fear, disgust or worry, or even big excitement. Nausea is the feeling of wanting to vomit, and just before you throw up, extra spit, called saliva, can fill your mouth.

Some causes travel in the blood. The brainstem has a trigger zone that senses chemicals travelling in the blood, so some chemicals can start the urge to vomit. The area postrema, in the brain, works like a poison alarm: it senses chemicals in the blood and can start the urge to vomit. The brainstem helps decide when you throw up. Both of these work through chemicals in the blood.

Then there is motion. Cars and boats can leave some people dizzy and sick to their stomachs. Balance parts inside your ear sense motion. Those parts link to the area of the brain that controls vomiting, so being in a boat, car or plane can make some people feel sick. As of November 2026, the main scientific explanation for motion sickness is sensory conflict: the brain gets signals from the eyes, inner ears and body that do not match what it expects.

Kids and grown-ups are alike in some ways and different in others. Throwing up happens to most kids now and then, and it does not usually last long. Kids are more sensitive than adults, and their bodies can react to things that would not bother a grown-up. The basic body steps are the same in adults and children. Kids just trigger the reflex more easily. Babies often spit up small amounts of milk, which is different from throwing up, because throwing up takes strong muscle squeezes.

There is a cost to know about. Vomiting can use up a lot of the body's fluid and leave it short of water, which is called dehydration. Acid on teeth removes minerals and softens the enamel. If this keeps happening, the softened surface can wear away. After you throw up, drinking or rinsing with water helps protect the teeth. So the reasons range from germs to bad food to a bumpy ride, and 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

• norovirus: stomach bug virus
• reflex: automatic reaction
• sensory: about the senses
• conflict: clash
• enamel: outer tooth layer