Dandruff and Seborrheic Dermatitis: A Head Scratcher 394 Malassezia The microbial origin of dandruff centers on the causal role of yeasts of the genus Malassezia.29-30 The vast majority of recent data supports a direct causal link between Malassezia fungi and dandruff. First, effective treatment of the condition can occur with a wide range of material types, from zinc and selenium salts to highly specific azoles, with the only known functional link between these materials being antifungal activity.30 The second supporting factor is that improvement in dandruff correlates considerably with reduction in scalp Malassezia level.31-32 While the absolute level of Malassezia correlates less well with dandruff, its reduction amongst those individuals that express the symptoms strongly supports its role. Originally named Malassezia by Malassez in 1898,33-34 this genus was renamed and referred to as Pityrosporum during the second half of the 20th century.35-36 At one time, members of Malassezia were classified into two species: a lipid-dependent species, M. furfur, and a non-lipid-dependent species, M. pachydermatis. In the mid 1990s studies of the morphological, ultrastructural, physiologic and genomic differences in Malassezia led to the identification of multiple lipid-dependent species (including M. globosa, M. restricta, M. furfur, M. obtusa, M. slooffiae, M. sympodialis, M. japonica, M. nana, M. dermatis, and M. yamatoensis), in addition to the non- lipid-dependent, primarily zoophilic, species, M. pachydermatis. Use of molecular markers is generally required to correctly differentiate between the various lipid-dependent species.37-41 Although members of the normal cutaneous microflora, yeasts of the genus Malassezia have been known for many years to play a role in human skin diseases including dandruff, seborrheic dermatitis, pityriasis versicolor, and Malassezia folliculitis, and they may likewise play a role in the exacerbation of atopic dermatitis and psoriasis.42-43 The study of this genus has been complicated by their fastidious culture requirements and a complex series of changes in nomenclature.42 The one frequently cited exception to antifungal