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Flaking
of the skin on the scalp is called dandruff. It is a
papulosquamous disorder with distinctive distribution and
characteristic morphology. Severe variety of
dandruff, characterised by redness, scaling and itching, is called seborrhoic
dermatitis [SD]. It affects about 3-5% of general population, but
the life time incidence may be much higher. Men are more commonly
affected and tend to have more severe disease. It commonly occurs
in infants and in the 18-40 years age group. There is no evidence
of genetic predisposition and no evidence of horizontal
transmission. Severe SD is a manifestation of HIV/AIDS.
Factors
causing dandruff are:
- Maturation of
sebaceous glands: Influence of puberty and androgens
- Malassezia
yeast: Malassezia globosa, Malassezia restricta and
Malassezia furfur
- Host factors:
- Altered immunity
- Altered composition of sebum
such as increased triglycerides and cholesterol, decreased squalene and free fatty
acids (FFA)
- Type of skin (abnormal multiplication & keratinization)
Pathogenesis:
SD is
characterised by increased desquamation evidenced by increased
mitotic index and parakeratotic cells. The inflammation can be
immunogenic, resulting in an altered immune response to Malassezia
or non immunogenic, initiated by the Malassezia yeast itself.
Decreased levels of Interleukin 2 (IL2) and Interferon γ (IFNγ) result
in decreased cell mediated immunity and promote fungal growth. Increased
IL10 and IgE result in increased humoral response, promoting
inflammation. Non immunogenic mechanisms include the Lipid like
leukocyte activator (LILA) released by the Malassezia that induce
neutrophil chemotaxis, Malassezia lipase that acts on
triglycerides to release free fatty acids that act as irritants,
stimulating Neurokinin-1, CD16+ and compliments and the action of
Malassezia on human keratinocytes, resulting in the production of
IL-1b, IL-6, IL-8, and TNF-α, leading to neutrophil infiltration and
inflammation.
Precipitating/exacerbating
factors include:
-
Nutritional factors such as pyridoxine deficiency, biotin deficiency,
EFA deficiency
-
Dietary
factors such as high glycemic diet that can result in increased
triglycerides
-
Atopy
predisposes to SD and SD in turn may worsen atopic dermatitis. Whereas
infantile SD is commonly associated with atopic manifestations, adult SD
is seen with asthma, Hay fever, childhood dermatitis etc.
-
Minerals - Copper and magnesium excess
-
Humidity and temperature - Increased in winter, lesser in summer
-
Stress
- Increased MSH, melatonin and sebaceous secretion
SD may
be associated with:
Drugs
causing SD like eruption include Methyl dopa, cimetidine and
chlorpromazine. Antiepileptics may lead to SD secondary to biotin
deficiency.
Clinically, dandruff
manifests as greasy flaking of the scalp, sometimes associated
with redness and itching and acne-like rash (Pityrosporum folliculitis) on
the face, back and chest. On the face, seborrhoic dermatitis is
manifested as redness and scaling on the inner side of the eye brows,
glabella, sides of the nose, beard region and around the ears. Sometimes
this can lead to scaling, swelling and itching of the eyelid
margins.
Course:
Severity of dandruff keeps varying, often aggravated by stress,
tiredness and exposure to sunlight. In chronic cases, there is some
degree of hair loss which is reversible. SD may be complicated by
secondary bacterial infections and hair fall. Dandruff may accelerate
the onset of male pattern baldness. It can also sometimes cause
pigmentation on the face. Medications used for SD may result in
dermatitis.
Control measures: Regular hair wash (2-3 per
week), avoidance of diet rich in sugar and processed and refined food, avoidance of too much of hair oil
and avoidance of stress. A diet rich
in vitamins (biotin) and essential fatty acids is useful.
Treatment should
be done in consultation with a dermatologist and includes antifungal
shampoo and shampoos containing coal tar, selenium sulfide or zinc pyrethione. In the presence of severe scaling, salicylic acid
preparations are used and in the presence of redness, mild
anti-inflammatory preparations are prescribed. Oral antifungals are
given in case of extensive, severe disease and associated with acne-like
rash. Regular treatment is needed for many years.
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