Pus is a thick fluid produced in response to infection. This fluid is made up primarily of neutrophils, or white blood cells, which fight and kill bacteria. In most cases, the pus is white or yellowish in color, but it can also appear red, green, brown, or, in very rare cases, blue. The color of the pus depends largely on the infection that the body is fighting. Pus also varies in color depending on the other substances it contains.
While fighting an infection, the body will normally create white, yellow, or clear pus. White and yellow pus is created in response to common bacteria, such as Streptococcus pyogenes Y Staphylococcus aureus . This bacterium is responsible for dozens of different infections, ranging from minor skin conditions like pimples to deadly diseases like meningitis.
Although the presence of mild pus is common, it should not always be ignored. Since there are many serious causes of pus, the condition may need to be investigated by a medical professional. Depending on the amount of pus and the severity of the condition, antibiotics may be prescribed to help fight the infection.
Pus may also take on a reddish color. Red pus is usually due to blood mixing with the pus cells. This frequently occurs in urinary tract infections, as well as certain skin infections, such as pimples and boils. The presence of blood does not necessarily mean that the body is having trouble fighting the infection. A reddish color of pus usually just indicates that the skin has become very irritated.
Green is another common color of pus and could mean one of two things. This pus can be caused by Corynebacterium diphtheriae , which is a rare infection of the upper respiratory tract. Pus may also get a green coloration from an antibacterial protein called myeloperoxidase. This brightly colored protein is produced naturally by certain types of white blood cells.
Brown pus is a sign of an amoebic liver abscess, caused by the parasite Entamoeba histolytica . If left untreated, these abscesses can burst and spread infection to the lungs, brain, and heart. Symptoms of an amoebic liver abscess include abdominal pain, fever, chills, diarrhea, jaundice, joint pain, and weight loss.
Blue pus is the least common of all the different types of pus. This color of pus indicates an infection caused by Pseudomonas aeruginosa , which typically infects the urinary tract, pulmonary tract, lungs, kidneys, and blood. Burns are especially vulnerable to Pseudomonas aeruginosa . If left untreated, these infections can become fatal.