Dark pus can be caused by several specific types of relatively uncommon medical conditions. These conditions may produce pus with a dark brown, green, or purple color. In other cases, pus and blood may be found in the same area, and the mixture of these two substances can have a dark red appearance as a result of the presence of red blood cells in the mixture.
Pus occurs when the body is actively fighting off an infection. White blood cells target invading cells, and cells of both varieties die in large numbers. These cells and other associated biological byproducts of the body’s struggle with invading pathogens make up pus. Individual pus cells are typically whitish or yellow in color.
One of the very common causes of dark-colored pus is the mixture of ordinary blood cells with pus. This can occur when pus forms in an abscess or boil beneath the surface of the skin. Small blood vessels may be broken from pressure caused by an expanding boil or may rupture as a result of attempts to drain or puncture the boil.
In cases where dark pus is the result of this sort of mixture of blood and pus, there are few additional medical risks. Any boil or abscess that has burst should be treated as an open wound. This treatment will normally involve precautionary measures to prevent additional pathogens from infecting the body at the site of the wound. Medical advice should certainly be sought for larger boils or for those located on the face or in clusters, and it is best to err on the side of caution when deciding whether or not to seek a medical evaluation.
Other conditions may produce dark pus that is green or bluish in color. Certain bacteria produce chemicals that cause pus to take on a greenish hue. In other cases, the body’s response to particular types of infection may involve specific proteins that can also turn pus a shade of green. As a general rule, any large boil or other accumulation of dark-colored pus should be evaluated by a medical professional, as some infections can be quite serious and require medical treatment rather than home care.
Some patients may mis-identify other substances as pus. Tissue that has begun to break down as a result of a disease may have a foul smell and black appearance and be called “black pus”. This is not a true form of dark pus, but is indicative of a very serious medical problem that demands immediate attention. Other bodily discharges may have the same consistency as pus but very different underlying causes.