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Cerumen

Cerumen, commonly known as earwax, is a yellowish, waxy substance secreted in the ear canal of humans and many other mammals. It plays a vital role in the human ear canal, assisting in cleaning and lubrication, and also provides a degree of protection from bacteria, fungus, and insects. A comprehensive review of the physiology and pathophysiology of cerumen can be found in Roeser and Ballachanda (1997).

Production

Cerumen is produced in the outer third of the cartilaginous portion of the human ear canal. It is a mixture of viscous secretions from sebaceous glands and less-viscous ones from modified apocrine sweat glands (Alvord & Farmer, 1997). Cerumen is genetically determined Asians and Native Americans are more likely to have the dry type of cerumen (grey and flaky), whereas Caucasians and Africans are more likely to have the wet type (honey-brown to dark-brown and moist; Overfield, 1985). In fact, cerumen type has been used by anthropologists to track human migratory patterns, such as those of the Inuits (Bass & Jackson, 1977).

Function

Cleaning: Cleaning of the ear canal occurs as a result of the "conveyer belt" process of epithelial migration, aided by jaw movement (Alberti, 1964). Cells formed in the centre of the tympanic membrane migrate outwards from the umbo (at a rate equivalent to that of fingernail growth) to the walls of the ear canal, and accelerate towards the entrance of the ear canal. The cerumen in the canal is also carried outwards, taking with it any dirt, dust, and particulate matter that may have gathered in the canal. Jaw movement assists this process by dislodging debris attached to the walls of the ear canal, increasing the likelihood of its extrusion.

Lubrication: Lubrication prevents desiccation and itching of the skin within the ear canal (known as asteatosis). The lubricative properties arise from the high lipid content of the sebum produced by the sebaceous glands. In wet-type cerumen at least, these lipids include cholesterol, squalene, and many long-chain fatty acids and alcohols (Harvey, 1989; Bortz et al., 1990).

Antibacterial and antifungal roles: While studies conducted up until the 1960s found little evidence supporting an antibacterial role for cerumen (e.g. Perry & Nicholas, 1956), more recent studies have found that cerumen provides some bactericidal protection against some strains of bacteria. Chai and Chai (1980), and Stone and Fulgham (1984), found cerumen to be effective in reducing the viability of a wide range of bacteria (sometimes by up to 99%), including Haemophilus influenzae, Staphylococcus aureus, and many variants of Escherischia coli. The growth of two fungi commonly present in otomycosis was also significantly inhibited by human cerumen (Megarry et al., 1988). These antimicrobial properties are due principally to the presence of saturated fatty acids, lysozyme and, especially, to the relatively low pH of cerumen (typically around 6.1 in normal individuals; Roland & Marple, 1997).

Removal

Excessive cerumen may impede the passage of sound in the ear canal, causing conductive hearing loss. It is also estimated to be the cause of 60 - 80% of hearing aid repairs (Oliveira, 1997). The most common method of cerumen removal by general practitioners is syringing. A curette method is more likely to be used by otologists and ENTs when the ear canal is partially occluded and the material is not adhering to the skin of the ear canal. It is usually necessary to soften wax before its removal, a process referred to as cerumenolysis.

While the removal of cerumen is a commonplace procedure, it is not without risk, and should be carried out by individuals who have been sufficiently educated and trained in the procedure.

References