A person with actinomycosis has a rare infection, caused by Actinomyces bacteria, which are present normally in the nose, mouth, throat, and intestine. Actinomycosis may occur in the face, jaw, neck, lung, or abdomen.

Actinomycosis infections tend to form abscesses, which are walled-off collections of pus. Pus is made up of infected tissue and white blood cells. The body forms a wall around the tissue in order to fight the infection. Actinomycosis may require long-term treatment with antibiotics. With early treatment, the infection resolves completely.