Download External Ear Keratin - Max Stanley Chartrand, Ph.D.

This article originally appeared in The Hearing Profesional July—August 2004
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Continuing Education: The Importance of the Keratin Layer to
Successful Fitting and Treatment
By Max S. Chartrand, BC-HIS
IHS offers a diversity of options for obtaining continuing education credit: seminars and classroom
training, institutional courses, online studies and distance learning programs. This article represents yet
another opportunity. Upon successful completion of the accompanying test you will earn one CEU.
The keratin or keratinocyte layer is the outermost portion of the stratum corneum or outer layer of
tissues of the external ear canal. Its physiological role is critical in maintaining homeostasis and adapting
comfortably to hearing aids and should garner the attention of every member of the hearing healthcare
team. Yet, though easily viewed through video otoscopy, its status often goes unnoted during the normal
course of dispensing activity.
Keratin is comprised of inorganic protein with no circulatory or neurological system. Chemically, its
structure is similar to that of human hair and nails. It completely covers the epithelial tissue, starting at a
point near the umbo of the tympanic membrane and then traveling the entire length of the canal lumen
to the aperture or opening of the ear canal.
Keratin protein is the most ignored part of the outer ear, yet it is vital for:
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maintaining pH flora to prevent fungus, yeast, bacterial infections
mixing sebaceous and ceruminous secretions
shielding the neuroreflexes from oversensitivity
adapting successfully to hearing aid earmolds
Figure 1
When the migrating keratin approaches the ear canal opening, it terminates just after contact with tiny
hair follicles that grow inward, forming a kind of “ramp” that lifts the desquamated (dead) keratin and its
cargo of debris from the epithelium. In turn, minute accumulations of dead skin cells, debris and earwax
are steadily deposited into the concha of the ear for easy removal.
Through otoscopy, keratin protein presents a “shiny” appearance. As underlying tissue grows steadily and
haltingly outward from the tympanic membrane, its migration causes a “bunched up” appearance,
forming circular “lines” around the wall of the ear canal. In cases of dehydration or in response to some
medications these lines can be so close together as to appear granular.
Undisturbed, keratin is what shields the ear canal from bacteria, fungus, yeast, amoeba and potentially
septic debris. It also helps the epithelium or outer layer of skin tissue—when coated with ceruminous and
sebaceous secretions (that together form “earwax”)—to maintain a slightly acidic pH environment of
about 6.5. Hence, keratin is the protective layer over the skin of the ear canal, without which the ear
canal would be more susceptible to invasion, injury and/or disease.
The absence of keratin in the ear canal may contribute to many common complaints among hearing
instrument users, such as:
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chronic itching
hearing aid earmold discomfort
non-acoustic occlusion (via the Arnold’s branch of the vagus)
predisposition for chronic externa otitis
Self-Cleaning Canal
The natural desquamation of tissue in the ear canal is such that tissue grows outward from near the umbo
(or center point of the eardrum) to the aperture of the ear canal. This natural process generally requires
about three months to travel the full length of the canal at the rate of about 1mm per day.
So, if one were to place a piece of sand on the tympanic eardrum today, about three months from now
that person could remove the same piece of sand from the bowl or concha of the ear with a fingertip.
Left undisturbed, then, healthy ear canals are self-cleaning and wax impaction is rare.
Abnormally low pH (below 6.5) often leaves the ear canal dry with a host of extant skin problems
(psoriasis, eczema, chronic external otitis, contact dermatitis, allergy and abnormal cell growth such as
basal and squamous cell carcinomas). After removal via cotton swab trauma or scratching with any foreign
object it requires about 10—14 days for a good, strong layer of keratin to reform. Hence, daily use of
cotton swabs will effectively negate its formation.
In addition, frequent use of ear preparations containing boric acid or hydrogen peroxide solutions not only
destroy keratin and layers of epithelium, they also eliminate the water repellent ability of same and
leave the external ear canal at risk for chronic otitis externa. Furthermore, these acids can inhibit
cerumen formation, as well as interrupt natural desquamation of tissue and the regrowth of the badly
needed keratin. Unfortunately, such harsh solutions are the mainstay of today’s over-the-counter
otopharmacopia.
Figure 2: Keratin coming up off of canal: Latent diabetes II case.
As a result of many years of experience working with hearing aid patients, this author believes that only
gentle, aseptic botanical solutions should be used in the ears, whether for the purpose of softening
hardened earwax or to nurture traumatized ear canal tissues back to normal homeostasis. In so doing,
natural tissue growth and its subsequent desquamation will help the canal resume its conveyor belt-like
process for self-cleaning and removing potentially harmful debris from the ear canal.
Some common and professional practices that remove vital keratin and can set up the external canal for
the above problems are:
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daily use of cotton swabs
insertion of foreign objects
frequent use of boric acid and hydrogen peroxide solutions
aggressive cerumen removal
overly tight oto blocks during impression taking
forcing one-size-fits-all earmolds into the ear
In cases where keratin has been removed due to any of the above described methods or has not formed
normally, especially in cases of abnormal pH (diabetes mellitus II, gout or thrush), a host of irritating,
potentially dangerous organisms such as fungi (aspergillus favus, etc.), yeasts (candida parapsilosis),
pseudomonas aeruginosa (gram positive) and streptococcus areus has been found.
Once the offending practices cease, periodic video otoscopic inspection should reveal ear canal
homeostasis returning to normal. Simultaneously, if there is not underlying pathology, patient complaints
usually subside. If not, medical referral may be indicated.
There is so much more to the discussion on keratin. It is often mistaken for earwax and, in cases of
chronically low pH, appears to peel off like snake skin as it separates early from underlying epithelium.
This is especially observed in cases of undisclosed or latent diabetes mellitus II and hyper/hypoglycemia,
a common pre-diabetic mellitus II condition. In our practice, we have also noted the association with
long-term semi-dehydration (often accompanied with hypernatremia or hypokalemia) and loss or
granulation of the keratin layer.
Additionally, a narrowly recognized yet potentially dangerous phenomenon arises when desquamated skin
cells mix with accumulated cerumen and peeled off keratin to form bacterial sepsis. Long-term impacted
earwax with offending bacteria and/or parasites can dry out and harden the wax. In these cases, gentle
softeners are indicated before removal.
External Canal Neuroreflexes That May Complicate HA Fittings
Neuroreflex
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Arnold’s branch of the vagus (Cranial X)
Lymphatic reflex (Cranial V and VII)
Red reflex (tympanic plexus of Cranial VII)
Indications During Dispensing Tasks
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Cough, non-acoustic occlusion, own-voice complaints
Increased tightness earmold over time, soreness
Induces need for more gain/output in amplification over time
Essential for Hearing Instrument Success
When it comes to wearing hearing aids, keratin status can be most crucial to success. Very few patients
can comfortably adapt to new hearing aids if the ear canal is in an unhealthy state. The essential layer of
keratin also shields the wearing of hearing aids and earmolds from the sensitive neural reflexes that arise
from compression of myelinated and unmyelinated nerve fibers of Cranials V, VII, IX and X that innervate
and traverse the external canal.
Unshielded, these sensitive reflexes can cause complications in hearing aid and earmold fittings. Some
natural neuroreflexes of the external ear canal, which can become particularly sensitive in the absence of
keratin are shown in Figure 3. Such complications are usually resolved by restoring the keratin layer,
following instructions for an appropriate wearing schedule, tapering the end of the offending earmold
and/or making impressions utilizing the (mid) open-mouth technique.
This author thinks that external ear physiology training should always include the importance of keratin
protein. It should be noted in all its normal and abnormal forms via video otoscopy and then discussed by
all members of the hearing healthcare team.
In doing so, we may more effectively reduce unnecessary shell and earmold remakes, returns for credit
and failed hearing aid trials. Additionally, we will further enlighten ideas about and approaches to ear
care, otoprosthetics and auditory rehabilitation.
Best of all, hearing impaired individuals will be more apt to enjoy the benefits of modern hearing
technology for improved quality of life, thus inducing a positive attitude about the care and services
available from their hearing professional and creating a win-win for all. THP
Max Chartrand serves as director of research at DigiCare Hearing Research & Rehabilitation in Rye,
Colorado, and has been actively involved in professional training in the hearing healthcare field for more
than two and a half decades. Correspondence: www.digicare.org.
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