When your child is sick you want to do whatever you can to get them better—fast. You bundle them up and take them to the doctor, expecting to get something to get rid of the illness, but you end up with a list of ways to treat the symptoms instead.

If you leave wondering why you didn’t get an antibiotic to fix the problem, you may need a quick lesson in what antibiotics are used for and what causes common illnesses—a virus or a bacteria. After all, antibiotics only work on bacteria.

Quick quiz: which illnesses are caused by bacteria and therefore require a trip to the doctor for an antibiotic? A cold? No. The flu? No. Stomach upset? Rarely. Ear infection? Maybe. Sinus infection? Maybe. Strep throat? Yes! It’s really the only common illness that affects kids that requires an antibiotic every time.

The others? Likely your doctor will recommend keeping your child home with plenty of fluids and rest, unless it’s been longer than two weeks without improvement.

“There’s a general misconception that kids need antibiotics when they’re are sick. Antibiotics are the exception more than the rule,” said a pediatrician with The Memorial Hospital’s Medical Clinic.

That’s because viruses cause many common illnesses and there is no cure for viral infections like there is for bacterial infections. Yes, there is flu prevention medicine such as Tamiflu but it doesn’t stop the flu in its tracks, rather it can shorten how long it lasts and lessen the severity of symptoms, if taken within 48 hours.

“Even ear infections can be viral and depending on the circumstances, we take a wait and see approach. The same is true for sinus infections. It’s usually when symptoms last more than 10 to 14 days that we worry it could be bacterial,” said a TMH pediatrician.

There are good reasons to avoid them when you don’t need them besides the fact that they won’t work. The big reason is because the overuse of antibiotics has caused some bacteria to become resistant to common antibiotics, making them ineffective.

“Bacteria becomes resistant to antibiotics over time, not only for the people who overtake them, but for the community as well,” said a TMH pediatrician. If you use antibiotics when you don’t need them, they might not work when you do.

Another reason to avoid antibiotics is because they not only kill dangerous bacteria, but also the helpful bacteria in our bodies. The human gut is full of bacteria that play an essential role in the immune system.