An infection is when microorganisms (germs) invade part of your body and make you sick.
"Micro" means small, so microorganisms are tiny living creatures. They're so small they can't be seen without a microscope. There are many different kinds of microorganisms, including:
The term "germs" refers to the different types of microorganisms that can cause disease.
Many germs don't cause infection. Some are even helpful. Many of the germs that live on your skin or in your body are normal and don't hurt you. These are called your resident flora.
An infection is caused by harmful germs entering your body. They can enter your body through:
Germs can get in your mouth if you eat or drink something with germs in it. They can also get in your nose or mouth if you touch something contaminated with germs and then touch your nose or mouth.
When they get into your body, harmful germs multiply and make you sick.
Sometimes the normal germs in your body get in the wrong place. For example, the normal bacteria in your intestines can cause an infection if they get into your bladder or into your bloodstream.
Your body has many ways to defend against infections:
Babies and very old people are more likely to get infections because their body's defenses aren't as strong.
Other things that increase your risk of infection include:
Diseases that weaken your immune system, such as AIDS, cancer, or diabetes
Drugs that interfere with your immune system, such as chemotherapy for cancer or corticosteroids
Medical devices in your body, such as IVs, tubes to drain urine (catheters), breathing tubes in your windpipe, or artificial joints
Radiation therapy for cancer
Symptoms depend on:
Infection in just one part of your body usually causes pain. For example, a lung infection (pneumonia) can cause chest pain. A brain infection causes headache. An infection under your skin (skin abscess) can swell up, turn red, and be painful.
Infections that affect a lot of your body can cause many different symptoms. Some common general symptoms include:
If you have an infection that isn't treated for a long time, you may lose weight.
Doctors suspect infection based on your symptoms. They usually don't do tests for common infections, such as colds and skin infections. For other infections, doctors often send a sample to the lab to test for germs. Depending on where the infection seems to be, they may send a sample of:
To prevent infections:
Wash your hands often, especially if you handle food or have a lot of contact with people
Get the vaccinations your doctor says you need