Dandruff and Seborrheic Dermatitis

Whether a result of accelerated cell turnover or due to fungus, these conditions can be controlled with OTC
products.

Dandruff and seborrheic
dermatitis are conditions that share a common manifestation: the patient's scalp
or skin produces scales. They may also share a common etiology. Many of the same nonprescription products will effectively treat both conditions.

Etiology

Abnormal Cell Turnover:

Epidermis is composed of five distinct layers. The innermost layer, next
to the dermis, is known as the stratum germinativum. Epidermal cells formed
here gradually begin to migrate upwards to the next layers, eventually reaching
the uppermost layer, the stratum corneum. By this time, they have lost their
nuclei and gained keratin, a tough substance. This process ensures that outer
skin can withstand the various minor environmental assaults to which it
is exposed. In other words, we are encased in a layer of dead, keratinized cells
that act to protect the living tissues beneath them. The time frame required for stratum
germinativum cells to lose their nuclei and become optimally keratinized is
25-30 days. For the most part, normal cell shedding is not noticed, and
causes no symptoms.




Proponents of the cell turnover
etiology of dandruff and seborrheic dermatitis assert that, for some patients,
cell turnover is accelerated. In dandruff, cell turnover is commonly 13-15
days. Seborrheic dermatitis may result from a cell turnover of only 9-10
days. The FDA OTC Review panel, in a 1982 report on dandruff and seborrheic
dermatitis, stated, "The cause of dandruff has not been clearly defined, but
it is known to involve an increase in the rate of epidermal turnover. This rapid
transit of cells to the surface does not allow for complete keratinization of
new cells."

¹

The FDA mentioned this etiology again in its consumer
publication in 1994, although it also briefly explored the theory of an invasive
fungus.

²

Fungal Etiology:

A great deal of research on dandruff and seborrheic dermatitis has centered
on the possible causative role of fungi. In 1873, a researcher affected with
seborrheic dermatitis of the beard isolated an organism that was also noticed
in 1874 by a researcher named Malassez. The fungus carried the name of the latter
investigator for decades, being known as

Malassezia furfur.


^3,4

While
many other names have been used for this organism, current practice is to call
it by a name it was given in 1913,

Pityrosporum ovale.

This lipophilic yeast
is known to be a normal inhabitant of human skin (follicles).

Although the fungal etiology
was once widely believed, it fell into disrepute for two reasons. One is that
there were no antifungals powerful enough to eradicate the condition. Another
is that corticosteroid therapy seemed to produce benefit, leading to the conclusion
that cell hyperproliferation might be the root cause.

At the time of the 1982
FDA OTC Review Panel Report, the view provided by the experts was: "Proponents
of this [fungal] theory support the use of antimicrobials in controlling dandruff,
but the Panel has concluded that there is not a definite correlation between
the presence of

P. ovale

and the development of dandruff."

¹

In 1984, however, a researcher
reviewed the literature, coming to the conclusion that

P. ovale

fulfilled all
of Koch's postulates for dandruff and seborrheic dermatitis.

⁵

Coupled
with the efficacy of ketoconazole in those conditions, medical opinion has slowly
begun to swing back toward the fungal etiology.

Current treatments for
dandruff and seborrheic dermatitis may in fact be effective through dual antifungal
approaches, if in fact the cell turnover theory has any validity.

Dandruff

Dandruff is a condition
of less severity than seborrheic dermatitis. If it is left untreated, the patient
will not experience any further symptoms. Although some patients may complain
of a minor itching from time to time, its effects are entirely cosmetic. It
does not cause or result from inflammation, and it is not allergic in origin.

Scaling of dandruff is
large clumps of dry, white or gray scales that are easily visible. An examination
of the scalp shows that borders are indistinct, but there are often several
roundish patches from which loose cells are shed. The crown is often a prime
location for cell loss.

Dandruff is uncommon in
children ages 2-10, but the incidence begins to rise precipitously as
patients approach puberty. From that time, dandruff incidence rises even more
rapidly until patients reach their early twenties, when it begins to fall. The
number of affected people drops slowly until it becomes uncommon in middle-aged patients and the elderly. There is no gender preference. As a male begins
to lose hair as the result of androgenic stimulation (androgenetic alopecia),
bald spots are typically dandruff-free.

Seborrheic
Dermatitis

Seborrheic dermatitis is
a more severe condition than dandruff. The scales appear to have an oily consistency,
and borders of the affected area are indistinct. The age of onset is usually
at puberty, and it is common to have pruritus associated with the condition.

Proponents of the proliferative
etiology point out that cell turnover is so rapid in dandruff that some cells
still retain their nuclei, and that in seborrheic dermatitis, the process is
further accelerated, with a correspondingly higher ratio of cells retaining
the nuclei.

The distribution of seborrheic
dermatitis lends credence to the fungal theory, in that

P. ovale

cannot
synthesize fatty acids of C

₁₂

or longer chain lengths.

⁴

Thus it is dependent on gaining these fatty acids from its surroundings. As
it metabolizes these fats, it may cause skin damage by producing irritant metabolites.

Treatment
Options

The original panel assigned
to review OTC products for dandruff and seborrheic dermatitis produced a document
in 1982, which was mostly affirmed (with few changes) in the final rule published
by the FDA in 1991.

⁷

Several ingredients were found to be safe and
effective for self-treatment of dandruff and seborrheic dermatitis in the 1991
final rule. Salicylic acid, selenium sulfide, zinc pyrithione and coal tar are
effective in treating both conditions while sulfur and ketoconzole are effective
in treating dandruff only and hydrocortisone is effective for seborrheic dermatitis
only. These products can treat patients aged 2 years and older except for ketoconazole,
which is not to be used to treat patients under the age of 12.

Salicylic Acid 1.8%-3%:

Salicylic acid is available in the form of shampoo and foam. It functions by
increasing the hydration of skin. Its mechanism may be lowering of the epidermal
pH, producing an inflammation that allows skin to retain water. This artificially
produced maceration causes the upper layer of the epidermis to shed. The keratolytic
action removes the scales of dandruff and seborrheic dermatitis.

Selenium Sulfide 1%

:

Selenium sulfide is highly active in inhibiting the growth of

P. ovale.

It is
also a proven cytostatic agent, slowing the growth of both hyperproliferative
and normal cells in dandruff and seborrheic dermatitis. A 0.6% micronized form
of selenium sulfide is also safe and effective for dandruff.

Zinc Pyrithione

:

Zinc pyrithione is safe and effective for dandruff in a 0.3%-2% concentration
shampoo, and for seborrheic dermatitis in a 0.95%-2% concentration shampoo.

Hydrocortisone 0.25%-
1%:

Hydrocortisone cream is safe and effective for treatment of seborrheic
dermatitis, but is not to be used to treat dandruff. This is because seborrheic
dermatitis has an inflammatory component, while dandruff does not.

Coal Tar 0.5%-5%"

:

Coal tar in its various forms (e.g., coal tar distillate, coal tar extract,
coal tar solution) is effective for both conditions, but is perhaps not the
best choice. In addition to its unpleasant odor, it can stain the skin and hair
(especially if the patient's hair color is naturally light [gray or blond])
or has been artificially bleached. It also can cause folliculitis, irritant
dermatitis, and allergic dermatitis. Coal tar may cause photosensitivity reactions,
and patients should be cautioned to avoid sun exposure for up to 24 hours after
using it. It is also potentially carcinogenic. This was demonstrated in a 1775
landmark study of chimney sweeps and their high incidence of scrotal cancer
being induced by exposure to soot and coal tar. Coal tar has caused a rash of
cancers in the anogenital area, leading to a precaution against application
to the rectum, genital area or groin for creams, ointments and lotions. If the
product is labeled for seborrheic dermatitis, the patient should be cautioned
to consult a physician before use if the condition covers a large part of the
body.

Sulfur 2%-5%

:

Sulfur, which is available in shampoo form, may function through a keratolytic
action. It is approved for dandruff in a 2%-5% concentration. It may also
be combined with salicylic acid for dandruff. The combination product is also
a shampoo.

Ketoconazole 1%


:
Ketoconazole 1% shampoo was recently switched from prescription to nonprescription
status. Its antifungal activity has been found to control the flaking, scaling,
and itching of dandruff safely in patients over the age of 12 years. The patient
is directed to use the shampoo every three to four days for up to eight weeks,
then as needed to control dandruff. If the condition worsens or fails to improve
in two to four weeks, the patient should see a physician. If the scalp


is broken or inflamed, the
patient should not use the product.