When you cut yourself, bacteria present in the soil and air enter the wound. At the same time, the blood in your body rushes to the size. The white blood corpuscles (phagocytes) in the blood engulf the invading bacteria. Blood platelets or red blood cells begin to clot, sealing the opening against further invasion.
The phagocytes continue to destroy the bacteria but many are overcome by the invaders. Dead bacteria, dead white blood cells, plasma and tissue from the injured cells collect to form pus.
Sometimes the collected pus and excess blood may cause the site of the cut to swell up and redden. This is called an abscess. It may be painful and requires antibiotics or draining of the pus by a doctor.
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