Atopic eczema/dermatitis syndrome and Malassezia

Atopic dermatitis is a chronic multifactorial inflammatory skin disease, which has had a marked increase in prevalence during the last decades. Recently, a new nomenclature was recommended where the term 'atopic eczema/dermatitis syndrome' (AEDS) should be used to reflect the heterogeneity in this group of patients and where those patients without measurable IgE reactivity should be classified as either 'nonallergic AEDS' or 'non-IgE-associated allergic AEDS'. For nearly 20 years it has been discussed whether the opportunistic yeast Malassezia, previously designated Pityrosporum, is a contributing factor to AEDS. Today there are several reports that demonstrate specific serum IgE or positive skin prick test and/or atopy patch test reactions to Malassezia in patients with AEDS. Several IgE-binding components have been identified in extracts of Malassezia ranging in molecular mass between 10 and 100 kD. The genes for nine Malassezia allergens with molecular weights ranging from 14 to 36 kD have hitherto been identified and cloned. Six of them are now produced by recombinant techniques and used in diagnostic tests. At present the genus Malassezia is subdivided into seven different species, which all have been isolated from human skin. The respective contribution of different Malassezia spp. to AEDS and in what proportion they share allergens remains to be clarified. We summarize here data that Malassezia can play a role in eliciting and maintaining eczema in patients with AEDS.