Scientists Say: Infection

Infections are caused by harmful organisms called pathogens entering the body

a teen boy sits on an exam table while a nurse pits a band-aid on his upper arm

Vaccines help protect from infections by training our immune systems to recognize and fight off pathogens.

Me 3645 Studio/Getty Images

Infection (noun, “In-FEK-shun”)

An infection occurs when harmful germs, or pathogens, invade the body and begin to reproduce. These pathogens can be bacteria, viruses, fungi or parasites. Some illnesses caused by infections are minor. For instance, most people recover quickly from germs that cause common colds. But other infections, such as the virus that causes rabies, are deadly.

Infections caused by different pathogens have different symptoms. Salmonella, for instance, is a type of bacteria that invades the intestines. Those infected often get diarrhea, fever and nausea. Athlete’s foot, on the other hand, is a skin infection caused by a fungus. It usually results in an itchy rash. Measles, meanwhile, is a viral infection. Symptoms often include a sore throat, cough, runny nose and skin rash­­­. Some of the symptoms sparked by an infection — such as a fever or headache — are caused by the immune system’s response to germs, rather than the germs themselves.

Infectious agents often enter the body through the nose, mouth or skin. Those germs can spread from person to person. For example, someone with COVID-19 can spew virus-loaded droplets into the air when they sneeze or cough. Someone else who inhales those droplets may become infected.

People can also pick up infections from contaminated food or water. Consider E. coli bacteria. Those germs sometimes live in uncooked meat. Someone who eats contaminated meat that has not been cooked enough may get an E. coli infection. Bug bites can spread infections, too. Some mosquitoes carry the parasite that causes malaria. And some ticks carry bacteria that lead to Lyme disease.

Vaccines help prevent many infectious diseases. They do this by training the body’s immune system to recognize and fight off pathogens. Someone may still get sick with an infection after being vaccinated. But their symptoms are usually much less severe than they would have been without the vaccine. That’s why it’s important to get vaccinated for infections such as COVID-19 and measles. Other healthy habits, such as washing your hands often, cooking meat thoroughly and using bug spray, can also ward off infections.

In a sentence

An infection caused by brain-eating amoebas, or N. fowleri, is almost always a death sentence.

Check out the full list of Scientists Say.

Maria Temming is the assistant editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

More Stories from Science News Explores on Health & Medicine