Endogenous factors - Abnormal sebum composition and commensal Malassezia furfur
One type of eczema, seborrhoeic dermatitis, appears in areas with active sebaceous glands. Infants suffer from seborrhoeic dermatitis due to maternal androgens inducing sebum production a few weeks after birth. However, the amount of sebum production does not correlate with the severity of the disease, implying that individuals with excessive sebum production might be free of eczema and vice versa. It has been proposed that an altered composition of skin surface lipids could be relevant for this disease (elevation of triglycerides and cholesterol, decrease of free fatty acids and squalene), but on the other hand, this could also result from ineffective keratinisation.
Also, the yeast Malassezia furfur (Pityrosporum ovale), a part of the normal resident skin flora, is supposed to trigger seborrhoeic dermatitis. Frequently, Malassezia furfur is present in this type of eczema, but the severity does not correlate with the amount of yeasts. However, as the clinical picture of seborrhoeic dermatitis ameliorates after application of antimycotic agents and worsens again when colonisation with Malassezia furfur increases, this yeast seems to be play an important etiologic role.
For the pathogenesis of seborrhoeic dermatitis, seborrhoe and abnormal sebum composition as well as the commensal yeast Malassezia furfur seem to be important factors. Their interaction is not fully understood up to now, though.