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Author: A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, 1997. Latest update by Dr Jannet Gomez, October 2017.
Seborrhoeic dermatitis (American spelling is ‘seborrheic’) is a common, chronic or relapsing form of eczema/dermatitis that mainly affects the sebaceous, gland-rich regions of the scalp, face, and trunk .
Dandruff (also called ‘pityriasis capitis’) is an uninflamed form of seborrhoeic dermatitis. Dandruff presents as bran-like scaly patches scattered within hair-bearing areas of the scalp.
The cause of seborrhoeic dermatitis is not completely understood. It is associated with proliferation of various species of the skin commensal Malassezia, in its yeast (non-pathogenic) form. Its metabolites (such as the fatty acids oleic acid, malssezin, and indole-3-carbaldehyde) may cause an inflammatory reaction. Differences in skin barrier lipid content and function may account for individual presentations.
Infantile seborrhoeic dermatitis affects babies under the age of 3 months and usually resolves by 6–12 months of age.
Adult seborrhoeic dermatitis tends to begin in late adolescence. Prevalence is greatest in young adults and in the elderly. It is more common in males than in females.
The following factors are sometimes associated with severe adult seborrhoeic dermatitis:
Seborrhoeic dermatitis affects scalp, face (creases around the nose, behind ears, within eyebrows) and upper trunk.
Typical features include:
Extensive seborrhoeic dermatitis affecting scalp, neck and trunk is sometimes called pityriasiform seborrhoeide.
Seborrhoeic dermatitis is diagnosed by its clinical appearance and behaviour. As malassezia are a normal component of skin flora, their presence on microscopy of skin scrapings is not diagnostic.
Skin biopsy may be helpful but is rarely indicated. Histological findings specific to seborrhoeic dermatitis are superficial perivascular and perifollicular inflammatory infiltrates, psoriasiform hyperplasia, and parakeratosis around follicular openings.
Treatment of seborrhoeic dermatitis often involves several of the following options.
In resistant cases in adults, oral itraconazole, tetracycline antibiotics or phototherapy may be recommended. Low dose oral isotretinoin has also been shown to be effective for severe or moderate seborrhoeic dermatitis.
Regular washing of the scalp with baby shampoo or aqueous cream is followed by gentle brushing to clear the scales.
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