Seborrhoeic dermatitis (American spelling is ‘seborrheic’) is a common, chronic or relapsing form of eczema/dermatitis that mainly affects the scalp and face. There are infantile and adult forms of seborrhoeic dermatitis. It is sometimes associated with psoriasis (sebopsoriasis). Seborrhoeic dermatitis is also known as seborrhoeic eczema.
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.
What causes seborrhoeic dermatitis? 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 form. Its metabolites cause an inflammatory reaction. Differences in skin barrier 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:
Oily skin (seborrhoea)
Familial tendency to seborrhoeic dermatitis or a family history of psoriasis
Immunosuppression: organ transplant recipient, human immunodeficiency virus (HIV) infection and others
Neurological and psychiatric diseases: Parkinson disease, tardive dyskinesia, depression
Seborrheic dermatitis is thought to be due to an inflammatory reaction against Pityrosporum ovale (called Malassezia furfur when in the infectious hyphal form),a yeast that is part of normal skin flora. The incidence of seborrheic dermatitis is associated with increased sebaceous gland activity and is found most commonly in infants and in post-pubertal patients.
Typical features include:
Winter flares, improving in summer following sun exposure
Minimal itch most of the time
Combination oily and dry mid-facial skin
Ill-defined localised scaly patches or diffuse scale in the scalp
Blepharitis: scaly red eyelid margins
Salmon-pink, thin, scaly, and ill-defined plaques in skin folds on both sides of the face
Petal or ring-shaped flaky patches on hair-line and on anterior chest
Rash in armpits, under the breasts, in the groin folds and genital creases
Superficial folliculitis (inflamed hairfollicles) on cheeks and upper trunk
Extensive seborrhoeic dermatitis affecting scalp, neck and trunk is sometimes called pityriasiform seborrhoeide