The term cerumen is generally considered to be synonymous with earwax, but technically it is not. Cerumen refers only to the secretory product of the ceruminous glands in the external auditory canal, and it is just one component of earwax. Other components include large sheets of desquamated keratin squames (the dead, flattened cells on the outer layer of the skin), sweat, sebum, and various foreign substances. These foreign substances can include any exogenous matter that is capable of entering the external ear canal--for example, hair spray, shampoo, shaving cream, bath oil, Cosmetics, dirt, and the like. The primary component of earwax is keratin.
The distinction between cerumen and earwax notwithstanding, for the purposes of this article, I will refer to both as cerumen.
Physical properties of cerumen
Cerumen has a surprising variety of colors, ranging from golden-yellow to light brown to dark brown to black. The true color of a cerumen bolus cannot be determined by just looking at it; you must smear a sample so that it thins out in order to determine its true color. The pigment responsible for the color of cerumen has yet to be identified.
One can look at the external ear canal as a simple skin-lined tube. The skin that lines the external ear canal is contiguous with the skin that covers the surface of the body. The epithelium of the skin on all other parts of the body sheds its keratin squames in response to friction caused by bathing, contact with clothing and bedding, etc. However, there is no friction inside the ear canal to promote the shedding of the superficial layer of keratin. In response to this limitation, the ear canal has developed a technique called migration. Migration is a mechanism by which the superficial keratin squames move laterally from the eardrum to the outer ear.
Different types of cerumen
Cerumen is classified as either dry or wet. Wet cerumen is subdivided as either soft or hard.
Dry vs wet. Orientals have a much different type of cerumen than do non-Orientals. The cerumen in Orientals--and only in Orientals--is a dry, flaky, golden-yellow keratin squame known as rice-bran wax. Cerumen in non-Orientals is brown and wet, and it can be either soft or hard (figure). There is a hereditary mechanism behind the development of cerumen in that the dry cerumen allele is recessive to the wet allele. Interestingly enough, rice-bran wax is associated with a lower incidence of breast cancer. But perhaps this should not be surprising because both the ceruminous glands and the breasts are exocrine glands.
Soft vs hard. Aside from the obvious, several factors differentiate soft and hard cerumen:
* Soft cerumen is more common in children, and hard cerumen is more common in adults.
* Soft cerumen is moist and sticky, whereas hard cerumen has a dry, desiccated consistency.
* In soft cerumen, the sheets of keratin squames are small. In hard cerumen, the sheets are large, dense, and much more prominent.
* The corneocytes are expanded in soft cerumen, but not in hard cerumen.
* Hard cerumen is more likely to be impacted, and it is the type we usually see in office practice.
Causes of accumulation
The cause of cerumen accumulation is probably a failure of corneocyte separation. Dermatologists see a number of conditions that they call corneocyte retention disorders, and that is what cerumen accumulation appears to be.
Keratosis obturans. Some patients have a plug in the ear canal that is pearly white and is completely made up of densely compressed keratin squames. This type of plug is extremely difficult to remove. Left untreated, the keratin sheets will continue to desquamate into the lumen of the external auditory canal and the mass will continue to enlarge. Over time, the pressure of this expansion can cause erosion of the bony canal.
While doing research at the University of Toronto, we hypothesized that cerumen impaction is not a result of overproduction in the ceruminous glands, but a failure of individual corneocytes in the stratum corneum to separate. In normal individuals, corneocytes separate from each other as the stratum corneum migrates laterally from the deep external auditory canal through the deep superficial junction. As a consequence of this failure to separate, the large keratin sheets are not carried out by normal migration. Instead, they accumulate in the deep canal.
We postulated that patients whose corneocytes fail to separate probably lack some substance that destroys the attachments that bind individual corneocytes to each other, thereby maintaining the integrity of the superficial keratin layer. We called this missing ingredient keratinocyte attachment-destroying substance (KADS). It is our theory that KADS releases those attachments and allows the cells to break down into individual flakes and desquamate. In patients who do not have KADS, the keratin sheet does not break down as it reaches the superficial canal; instead, it maintains its integrity. As a result, it tends to roll back on itself, accumulate, and become coated with cerumen. Eventually, it forms a plug.
Our theory holds that cerumen accumulation is a medical disorder rather than a natural phenomenon. It is probably a disorder of the migratory epithelium in the superficial external auditory canal, and it is probably genetic.
Possible KADS. We believe that there might be more than one KADS and that one of these substances might be steroid sulfatase, which is an aryl-sulfatase-C enzyme. Steroid sulfatase is normally present in epithelial cells, fibroblasts, and leukocytes. It is the only enzyme known to be involved in the process of epidermal cell desquamation.
The cohesion of the cells of the stratum corneum is maintained by cholesterol sulfate, which acts as an intercellular cement. Steroid sulfatase is believed to block the action of cholesterol sulfate and allow the bonds to become free of each other. Our research shows that in normal individuals, steroid sulfatase activity is greater in the epithelium of the deep external auditory canal than it is in the superficial external canal. Therefore, steroid sulfatase appears to be responsible for the separation of the keratinocytes as they migrate outwardly. Steroid sulfatase is responsible for an X-linked recessive ichthyosis (a corneocyte-retentive condition in which scales of keratin adhere to the skin). Over time, these keratin scales accumulate and turn dark brown. We believe that a similar mechanism is primarily responsible for cerumen accumulation.
There is a great need for a better ceruminolytic. A ceruminolytic should disrupt the structural integrity of the keratin sheets and thereby soften, loosen, liquefy, and/or dissolve cerumen and perhaps even float it out. The integrity of the cell membrane is thus reduced, which allows water to pass into the corneocytes along an osmotic gradient. The hydration causes the corneocytes to swell and fragment. The aim of ceruminolysis is to disrupt the keratinocytes on the outside of the plug, as well as those that are located between the plug and the ear canal. Once this is accomplished, the cerumen can be removed by curettage, aspiration, or microdebridement.
The two types of available ceruminolytics are aqueous and organic. Among the aqueous solutions are ordinary water, 10% sodium bicarbonate, 3% hydrogen peroxide, 2% acetic acid, and a combination of 0.5% aluminum acetate and 0.03% benzethonium chloride. Overall, aqueous solutions do a fairly good job of expanding and loosening or dissolving cerumen plugs. Oil-based organic solutions include olive oil, glycerin, propylene glycol, spirit of turpentine, and liquid paraffin. They basically do nothing but lubricate. They do not dissolve or expand corneocytes, and as a result they have no effect on the structural integrity of keratin squames.
Some ceruminolytics--particularly the organic solutions--can cause sensitivity reactions, such as contact dermatitis. Also, a failure to remove cerumen completely can result in a fungal superinfection. Another possible complication is ototoxicity, which can occur if a perforation is present. In many patients, a cerumen plug blocks the view of the tympanic membrane, so we cannot know for certain whether a perforation is present. Nevertheless, we can make an educated guess with a reasonable degree of reliability.
The speed of a particular ceruminolytic's action depends on the removal technique you will use, the amount of cerumen, the hardness of the cerumen (i.e., its keratin content), and the temperature of the ceruminolytic.
Dr. Croxson: Aside from being more comfortable for the patient, why does warming a ceruminolytic help?
Prof. Hawke: I'm not sure why it works, I just know that it does. We know that cerumen stays hard longer in a cold ceruminolytic. Perhaps there is some substance in cerumen that is temperature-sensitive.
Michael Hawke, MD
Prof. Hawke is in the Department of Otolaryngology at the University of Toronto. His research interests include ear disease, sleep disorders, and sinus disease.
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