Furunculosis also results in painful swelling. Once the skin is broken, germs, fungus, or bacteria can invade the tissues of the canal. Sometimes the Pseudomonas aeruginosa bacterium, which lives in the inadequately chlorinated water of a public pool, is the infecting agent. On rare occasions, external otitis is caused by a fungus, usually Aspergillus niger, which produces coal-black spores like those often seen on old bread. It may become so firmly entrenched that it remains even after the eczema is healed.
Furunculosis is caused by an infection of a hair follicle in the ear canal.
The physician diagnoses these conditions by physical examination, observing the symptoms. Aspergillus niger infection is identified by the characteristic color of the spores in the ears. A culture can identify the bacteria. Aspergillus niger is easily treated with a dusting of sulfanilamide powder. Furunculosis may be treated with systemic antibiotics as well as ear drops.