It often occurs in the summer, especially after swimming in polluted water. Furunculosis, or recurring boils, is similar to external otitis, but only the hair follicles in the ear canal are infected. External otitis usually starts with itching of the ear and may develop into very severe pain, caused by swelling of the tissue in the canal pressing against the bone.
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.