A white cell (or white blood cell) is a type of cell in your blood that fights off germs and helps keep you healthy. While red blood cells carry oxygen throughout your body, white cells act like your body's defense force, patrolling for invaders like bacteria and viruses.

When you get a cut or catch a cold, white cells rush to the problem area. Some white cells surround and destroy germs directly, like soldiers in battle. Others produce special proteins called antibodies that tag germs for destruction or help your body recognize them faster next time. This is why you usually don't get chickenpox twice: your white cells remember the virus and attack it quickly if it returns.

Unlike red blood cells, which all look similar, white cells come in several different types, each with its own job. When you're sick, your body creates more white cells to fight the infection. Doctors can count your white cells with a blood test to see if you're fighting an illness. A high white cell count often means your body is battling an infection, while a normal count suggests you're healthy.

Your bone marrow produces millions of new white cells every day, constantly replacing old ones and keeping your immune system ready to protect you.