Seborrhoeic dermatitis
You know you have Seborrhoeic dermatitis when there are
greasy, red, itchy patches on the skin covered with flaky scales that are white
or yellow in color. On the scalp, the condition presents as severe dandruff
with some shedding of hair. Other affected areas are the sebaceous-gland-rich
areas of your skin such as eyebrows, the sides of the nose, backs of your ears,
chest, groin and occasionally the armpits.
Looking at your skin under a microscope, you will see your
tormentor, the microscopic yeast, Malassezia. It produces toxic substances that
irritate and inflame the skin. Although Malassezia grow on the skin of healthy
people as well, scalp swabs from sufferers with seborrheic dermatitis show
higher levels of colonization. Under the right conditions, Malassezia will
morph from a benign organism into a pathogenic one. Further evidence of this is
that the condition improves with antifungal treatment, accompanied by a
decrease in numbers of Malassezia on the skin.
Certain illnesses
If you have eczema anywhere on your body, it could also be
on your scalp, possibly leading to the development of dandruff.
Shedding of dead skin from the scalp of Psoriasis sufferers
may be interpreted as dandruff. Malassezia may play a role in psoriasis on the
face and scalp.
People with compromised immune system such as those with
HIV-AIDS and neuropsychiatrically impaired individuals have a higher incidence
of the condition.
Other diseases that increase your chance of developing
dandruff are: Autoimmune and neurological disorders such as Parkinson's disease
and systemic lupus erythematosus; Atopic dermatitis, Pityriasis rosea, Tinea
capitis, Polycystic ovary syndrome etc.
Genetics
Some of the above diseases have genetic basis. Studies have
found that people who are sensitive to yeast have a slightly higher risk of
having dandruff. There may be a genetic predisposition for them to be more
vulnerable to yeast infection.
Another study found an ABO blood group predisposition. A large
number of people screened in the study were carriers of Malassezia species, but
only a very small group had dandruff. The researchers concluded this clearly
establishes the fact that a benign yeast can transform and become saprophytic to
feed on dead skin of some individuals in the population. However, they have not
established the triggers for the transformation to occur.
Males are more susceptible to dandruff than females.
Researchers have shown that testosterone stimulates the growth of certain dermatophytes
(infectious fungi on keratin), while estrogen inhibits the same.
INFECTION
Since Malassezia is frequently associated with dandruff, let
us take another look at this organism. It was first identified as yeast found
on the skin of patients with dandruff in the 19th century. Bizarrely,
this organism can morphs into a fungal (hyphal) form and/or both. Its hyphal
form predominates in skin diseases such as tinea versicolor and Pityrosporum
folliculitis.
The hyphae filaments used to be called 'Malassezia' and the
yeast forms were called 'Pityrosporum' because scientists thought they were two
different organisms. Then in the 1980s,
molecular methods of species identification showed they were two forms of the
same organism. Malassezia don’t have the ability to make its own saturated
fats. Therefore, it feeds on saturated fats on our skin. In its fungal form, it
feeds on our dead skin as well.
Like the chicken and egg question, scientists could not
determine whether abundant dandruff on our skin encourages Malassezia to
proliferate or increased yeast cells irritates our skin and triggers increased
scaling.
However, predisposing factors to Malassezia skin disease
include:
- Warm, humid condition, including sweating. Hence, pityriasis versicolor is common in tropical areas.
- Oily skin hence it is found mainly on oil-gland-rich areas such as the scalp, face and upper trunk.
Frederick Manuel and S Ranganathan postulated “on Two Stages
of Dandruff” that “Malassezia colonization is a secondary event in dandruff.
And
Suggested that a cascade of events preclude dandruff
formation”
The two stages in infection of dandruff sufferers are:-
Stage 1
- At the Primary stage, there are multiple host-specific predisposing factors.
- Multiple nonspecific factors can trigger dandruff. They are of non-microbial origin.
Stage 2
- The secondary stage has multiple microbial causes.
- Response varies according to each individual.
(International Journal of Trichology,
2011)
