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:
- Parkinson’s disease
- Mood disorders
- Diabetes mellitus
- Myocardial ischemia
- Dyslipidemias
- Obesity
- Epilepsy
- Malabsorption
- Alcoholism
- Alcoholic pancreatitis
- Psoriasis – sebopsoriasis
- Atopic dermatitis
- Acne
- Rosacea
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.