An infection occurs when harmful germs like bacteria, viruses, or fungi invade your body and start multiplying, making you sick. When you catch a cold, get strep throat, or develop an ear infection, these microscopic organisms have gotten past your body's defenses and begun causing problems.

Your body fights infections constantly. Your skin acts as a protective barrier, while your immune system attacks invaders that get through. When you get a cut and don't clean it properly, bacteria might enter and cause an infection, making the area red, swollen, and painful. That's your body battling the germs and trying to heal.

Different infections require different treatments. Antibiotics can kill bacterial infections like strep throat, but they're useless against viral infections like the common cold. Your doctor must identify what kind of infection you have before choosing the right medicine.

Some infections spread easily from person to person. When someone with the flu coughs near you, they might spread the infection through tiny droplets in the air. This is why washing your hands and covering your mouth when you cough helps prevent infections from spreading. The word can also describe the process itself: a wound might become infected if germs get into it.