Skip Ribbon Commands
Skip to main content
Health Issues

How Do Antibiotics Work?

How Do Antibiotics Work? How Do Antibiotics Work?

Antibiotics are powerful medicines to fight certain germs, but they aren't the answer for every infection your child gets. In fact, there are two major types of germs that cause most infections⁠—viruses and bacteria⁠—antibiotics are useful only against bacteria. Here's what parents need to know.

What are bacteria?

Bacteria are one-celled organisms that are just a few thousandths of a millimeter in size. They live on our skin, in our digestive system and in our mouths and throats. In fact, there are one hundred trillion bacteria living and thriving on or inside of us. Most are either harmless or serve a purpose in the body (such as helping to break down the nutrients in our diet). However, some bacteria are dangerous and cause illnesses. Harmful bacteria are responsible for many childhood diseases, like strep throat or urinary tract infections.

What are viruses?

Viruses are even smaller than bacteria—1,000 times smaller. Despite their size, viruses can cause diseases when they enter healthy cells in the body. They're responsible for the common cold, the flu and most sore throats and coughs. They also cause smallpox, the measles, the mumps, hepatitis, and acquired immunodeficiency syndrome (AIDS).

As powerful as antibiotics are when used in the right situations, they cannot kill viruses, and they do not work against viral infections. If they're given to your child when they have a viral infection, they can cause side effects. Taking antibiotics when they're not needed can also add to the serious problem of antibiotic resistance and difficult-to-treat "superbugs."

There are drugs called antivirals that have been developed to fight a few types of viruses. However, there are currently no antiviral medicines to treat the most common viruses that cause sore throats, coughs and runny noses.

Are antibiotic medicines available in different forms and types?

Antibiotics are available in several forms for children. These include tablets, capsules, liquids and chewable pills. Some antibiotics come as ointments and others come as drops (such as for ear infections).

There are also many types of antibiotics. Some, such as penicillin, kill bacteria by destroying the bacterial cell wall. Others, such as tetracycline, interfere with the ability of bacteria cells to reproduce or make proteins or nutrients they need to survive. When your pediatrician prescribes an antibiotic, they will choose the best one for the specific germ that is making your child sick.

What are broad-spectrum antibiotics?

Some antibiotics are called broad-spectrum and can fight many types of germs in the body, while others are more specific. It's best to use the most narrow-spectrum antibiotic that will only fight the germ that's causing the infection. Sometimes, your pediatrician can use a test to identify the specific bacteria causing your child's infection, which helps target those germs without killing other "good" bacteria.

What are some possible side effects of antibiotics?

As powerful and useful as antibiotics can be, they can have side effects. In children, they can cause stomach discomfort, diarrhea and/or nausea. Some children have an allergic reaction to penicillin and other antibiotics, producing symptoms such as severe skin rashes or breathing difficulties. If you think your child could be having an allergy to an antibiotic, call your pediatrician right away.

Are antibiotics ever used to prevent illnesses?

While antimicrobial drugs are mostly used to treat infections that your infant or child may develop, they are sometimes prescribed to prevent an illness from developing. For example, children who have frequent urinary tract infections are sometimes given antibiotics to reduce the likelihood that they'll recur. These medicines can kill the bacteria before they have a chance to cause an infection.

Other times preventive antibiotics may be prescribed for children could be after a dog or animal bite or before an operation. These "prophylactic" antibiotics should always be given for the shortest period possible to reduces the chances of side effects or creating antimicrobial resistance.


If your child has a cold, antibiotics aren't the answer. It's sometimes difficult for parents to determine if their child's illness is caused by viruses or bacteria. For this reason, never try to diagnose and treat your child's illness yourself. Contact or visit your pediatrician's office.

More information

Last Updated
American Academy of Pediatrics Section on Infectious Diseases (Copyright © 2022)
The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
Follow Us