A white blood cell is a type of cell in your blood that fights infections and helps keep you healthy. While red blood cells carry oxygen around your body, white blood cells act like your body's defense force, attacking germs, viruses, and anything else that might make you sick.

Your body makes white blood cells in your bone marrow, the spongy tissue inside your bones. When germs invade your body, these cells spring into action. Some white blood cells swallow up bacteria like tiny Pac-Man. Others make special proteins called antibodies that stick to germs and mark them for destruction. Still others remember infections you've had before, so they can fight them faster if those same germs return.

When you get a cut that becomes infected, the area might look swollen and turn red or even yellowish. That's partly because white blood cells are rushing to the injury site to fight the bacteria. Doctors can count your white blood cells in a blood test. If you have too many, it might mean your body is fighting an infection. If you have too few, your immune system might be weakened.

Unlike red blood cells, which all look similar, white blood cells come in several varieties, each with its own special job in protecting you. Together, they form a crucial part of your immune system, the network that defends your body against disease.