Teun Boekhout (editor) - Malassezia and the Skin: Science and Clinical Practice

Roderick J. Hay 1 and Gillian Midgley

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Core Messages

The history of the recognition of the significance of the Malassezia yeasts and their potential role in causing disease in humans and animals is one of the more intriguing medical stories of the last 150 years. It contains all the elements of a classic mystery, from the early proposed association between an unusual looking organism seen in the skin diseases, seborrhoeic dermatitis and pityriasis versicolor, to its reclassification into a number of different species on the basis of molecular taxonomy. In the intervening period, other important discoveries were made. Its presence on normal skin indicated that it was a skin commensal, yet the argument over its true identity and nomenclature form a key part of this story. It was accepted at first as a cause of seborrhoeic dermatitis, but then rejected before the argument swung back in favour of a causal link in the late 1980s. While it has always been accepted as a cause of pityriasis versicolor, the new molecular work has allowed for the initiation of investigations to relate different clinical forms to individual species. The association of Malassezia species with animal disease has been an important development in veterinary medicine as skin disease caused by these organisms is very common in certain breeds. More recently, it has been reported that Malassezia species can be a cause of systemic infection, particularly in new born infants, and that it may also contribute to allergic disorders such as atopic dermatitis. As is often the case, the molecular work has outpaced the definition of clinical states, and it will be necessary to re-examine the status of individual diseases and reconsider whether they should be subdivided further. Early difficulty in the isolation of these lipophilic yeasts in the laboratory held back research, but the introduction of molecular methods has expedited work on the genus in recent years. This has contributed to our understanding of its pathogenesis, epidemiology and even its management. For instance, it has provided a more robust method of designing intervention strategies, such as the use of appropriate antifungals, as different species exhibit different drug sensitivity patterns.