The ear is divided into three separate compartments: the inner, middle, and outer ear. The inner ear contains the balance organs and the nerves vital to hearing. The middle ear contains the bones that link the eardrum to the inner ear. The eardrum separates the middle and outer ears. The outer ear is simply the earlobe and a short tube leading to the eardrum.

Infection of the inner ear is called labyrinthitis. Infection of the middle ear is called otitis media. It can cause temporary hearing loss and can progress to the inner ear if ignored. Infection of the outer ear is called otitis externa or swimmer's ear. It’s rarely serious.

Outer ear infections can be acute (short-term) or chronic (lasting 3 or more months) and are more common in children 7 to 12 years of age. Outer ear infections also more commonly affect people in warm and humid climates, people who swim, and people who use devices that protect hearing.

Swimming isn't the only way to get an outer ear infection. You can also be infected if hairspray or other liquids get into the ear canal. The bacteria (and occasionally fungi) that cause an outer ear infection don't necessarily live in the water. Many of them are already in the ear canal or are picked up in everyday life. However, water or other foreign liquids in the ear can provide an ideal breeding ground for them.

You can also trap bacteria in the ear by using cotton ear swabs. The skin of the ear canal slowly moves outward like a conveyor belt, carrying shed fragments of skin away from the eardrum. Pushing a cotton swab into the ear goes against this process, and causes dead skin and earwax to build up. Occasionally, scratching the ear canal can also promote infection. This tends to trap moisture in the ear. Moist skin and tissue create a friendly environment for bacteria and allow them to multiply, causing infection.

People with the following conditions get outer ear infections more easily:

• allergies
• eczema
• psoriasis
• seborrheic dermatitis (in which dandruff is the most common symptom)

The main symptoms of an outer ear infection are severe pain, itching, or redness in the ear and tenderness in the earlobes.

The tissue in front of and below the ear may become swollen and tender. There's often a lot of earwax and skin debris in the ear canal. More severe bacterial infection sometimes causes yellowish pus to drain out. This may have an unpleasant smell. Fungal infections can create a grey-white pus.

Pus, wax, and skin debris may block sound waves from reaching the eardrum, causing temporary reduced hearing. This isn't a sign of ear damage. Generally, you don't need to worry about the infection spreading to the middle or inner ear, as the eardrum won't let fungus and bacteria to pass through. The middle ear is usually only infected through the tubes that connect it to the throat (the Eustachian tubes). The eardrum itself is not as delicate as most people think.

Complications of outer ear infections are extremely rare, except in people with diabetes or with weakened immune systems. One of the ear's main ways of defending against bacteria is the acidity of earwax. Unfortunately, earwax in people with diabetes is often quite alkaline. A low level of acid in earwax encourages particularly severe infections that can spread into the surrounding bone. This is called malignant otitis externa.

A doctor will check to see if pulling the earlobe gently or pushing the tragus, the small flap of ear just in front of the canal opening, causes pain. If these symptoms are present, you can be pretty sure it's an external infection and not otitis media.

The doctor can often make the diagnosis simply by looking in the ear with an otoscope (an instrument for examining the ear).

A lab culture may be ordered to identify the particular organism only if the first treatment recommended by the doctor doesn't seem to be working.