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Page: Causes, Incidence, and Risk Factors
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Swimming in polluted water is a common way to contract swimmer's ear, but it is also possible to contract swimmer's ear from water trapped in the ear canal after a shower, especially in a humid climate. Even without exposure to water, the use of objects such as cotton swabs or other small objects to clear the ear canal is enough to cause breaks in the skin, and allow the condition to develop. Once the skin of the ear canal is inflamed, external otitis can be drastically enhanced by either scratching the ear canal with an object, or by allowing water to remain in the ear canal for any prolonged length of time.
The two factors that are required for external otitis to develop are (1) the presence of germs that can infect the skin and (2) impairments in the integrity of the skin of the ear canal that allow infection to occur. If the skin is healthy and uninjured, only exposure to a high concentration of pathogens, such as submersion in a pond contaminated by sewage, is likely to set off an episode. However, if there are chronic skin conditions that affect the ear canal skin, such as atopic dermatitis, seborrheic dermatitis, psoriasis or abnormalities of keratin production, or if there has been a break in the skin from trauma, even the normal bacteria found in the ear canal may cause infection and full-blown symptoms of external otitis.
The incidence of otitis externa is high. In the Netherlands, it has been estimated at 12-14 per 1000 population per year, and has been shown to affect more than 1% of a sample of the population in the United Kingdom over a 12 month period.
Characteristics of the external ear leading to external otitis
The outer ear canal starts at the opening on each side of the head that allows the entry of sound; the skin-lined canal extends in as far as the tympanic membrane (ear drum). The surface of the ear drum is also skinlike, and is continuous with that of the ear canal. There are two distinct parts to the ear canal, the outer portion, which lines the cartilage portion of the ear canal that travels through the soft tissues of the head, and the inner portion, which lines the bony ear canal that travels through the skull. The bony ear canal can be seen on preserved specimens of the skull. The skin that is most easily inflamed is the delicate skin of the inner portion, the thin closely applied skin of the bony ear canal, which is perhaps the only skin of the body that ordinarily should never be touched!
The skin of the ear drum surface and the ear canal is much like skin anywhere on the body, it is waterproof because of layers of keratin at its surface. These surface layers are shed, but do not normally build-up in the ear canal. That's because of the way that the skin grows: migrating outward along the canal to the surface of the head and bringing any surface debris with it.
The outer ear canal skin is much thicker and more resilient to injury than the skin of the bony canal. This outer canal skin has a thick layer of subcutaneous tissue cushioning it, and contains both hairs and cerumen glands. The cerumen glands produce ear wax that is normally protective.
A folliculitis of one of the hairs of the outer portion of the ear canal can be the start of a bout of external otitis. Impaction of cerumen that abuts up against the delicate skin of the bony canal, or attempts to remove the impacted wax, can also be the initial event.
The S-shape of the ear canal, the presence of hair in the outer part, and the outward migration of skin all combine to help shed water from the ear canal and keep shed skin from building up within the canal, as well as to keep water from pooling in the innermost canal. In some minor malformations of the ear canal or auricle, the size and shape of the canal may pre-dispose allowing water that enters the ear to remain, or to inhibit the normal shedding of superficial skin and cerumen from the ear canal. In such cases, the individual may have a predispostion to recurrent external otitis.
Pathogens - The Disease-Causing Germs
The bacterial pathogens at the top of the list are Pseudomonas aeruginosa and Staphylococcus aureus, followed by a great number of other gram-positive and gram-negative species. Candida albicans and Aspergillus species are the most common fungal pathogens responsible for the condition.
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Important notice:
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
qualified health provider with any questions you may have regarding a medical condition.
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