A collection of pus in a wound is a sign of infection. Pus consists of dead skin cells; white blood cells, or leukocytes; and the bacteria causing the infection. One of the most common types of bacteria that can cause pus in a wound is Staphylococcus aureus, generally just called staph. Visible pus is one result of the body working to fight off the invading bacteria, whether it is staph or another variety.
The reason staph is commonly found in injuries is that it is present on many people’s skin, so when the skin is opened in any way the bacteria can easily get in. Once inside the body, bacteria can multiply and spread, causing the injury to become infected. One of the body’s defense mechanisms is to send white blood cells to consume the bacteria using a process called phagocytosis.
After about 12 hours the white blood cells die, while still containing the bacteria they have enveloped. They become part of the pus in a wound, which gives pus its characteristic white or yellowish color. Pus may take on other colors depending on what specific immune system reaction has been triggered or if there is any blood in it. The various colors, typically darker yellow, reddish-brown, or green, are not usually indicators of the seriousness of the infection. Green indicates the release of a natural antibacterial protein by the white cells, and red or brown usually signals that there may be some blood in the pus, but it is rarely serious.
Since pus in a wound typically contains live bacteria, it can transmit the infection from one person to another, or from one part of the body to another. It is important to always take precautions when dealing with pus, using disposable gloves when possible before changing dressings or handling the infected area. Bandages, swabs, and other materials used to clean the area should be handled carefully and disposed of properly to avoid spreading the infection.
In some cases the body is not able to deal with the infection, and the amount of pus in a wound will increase. There may also be red lines leading away from the injury; it may also feel hard, hot, or both, and the injured area may become swollen. Any of these symptoms are an indication that the infection is progressing and medical attention is required. An infection can spread quickly and staph can cause many problems in the body if not dealt with promptly.