Malassezia furfur is a lipophilic yeast considered a normal component of the human skin flora. Apart from pityriasis versicolor, M. furfur has been linked to several skin diseases such as dandruff/seborrhoeic dermatitis, folliculitis or atopic dermatitis. Six species within the formerly called M. furfur (lipid-dependent Malassezia strains) have now been identified: M. furfur, Malassezia sympodialis, Malassezia globosa, Malassezia obtusa, Malassezia restricta and Malassezia slooffiae.
The predominant species involved in the aetiology of dandruff/seborrhoeic dermatitis are M. globosa and M. restricta. These two species play a synergistic role in triggering or exacerbating dandruff/seborrhoeic dermatitis by degrading sebum. Modified sebaceous secretions penetrate hair follicle keratinocytes and stimulate a Th2 immune response that culminates in epidermal hyperproliferation, with a decrease in the epidermal transit time to 3-4 days.
Colonization of the scalp with M. globosa and M. restricta is necessary but not sufficient to cause dandruff/seborrhoeic dermatitis. Additional factors include the presence of sebaceous gland secretions and individual susceptibility.
Dandruff is treated by regular washing with Anti fungal shampoos active against Melassesia species. Potentially effective agents include zinc pyrithione, zinc omadine, selenium sulfide, ciclopirox olamine, miconazole and ketoconazole. However shampoo formulation is at least as important as the active ingredient in determining treatment success.