P10.132 Three etiologic facets of dandruff and seborrheic dermatitis:  Malassezia fungi, Sebaceous lipids, and Individual sensitivity

Yvonne M. DeAngelis¹, Meredith O. Leland¹, Teun Boekhout², Joseph R. Kaczvinsky¹, Shane Whitaker¹, Dianna Keanneally¹, James R. Schwartz¹ and Thomas L. Dawson, Jr.¹

¹The Procter and Gamble Company, Cincinnati, Ohio ²CBS, Utrecht, The Netherlands

Objectives: Application of new molecular and biochemical tools has greatly increased our understanding of the organisms, mechanisms, and treatments of dandruff and seborrheic dermatitis. Dandruff results from at least three etiologic factors: Malassezia fungi, sebaceous secretions, and individual sensitivity. While Malassezia (formerly P. ovale) has long been a suspected cause, implicated by its presence on skin and lipophylic nature, lack of correlation between Malassezia number and the presence and severity of dandruff has remained perplexing. We have identified the Malassezia species correlating to dandruff and seborrheic dermatitis and determined that dandruff is mediated by Malassezia metabolites, specifically irritating free fatty acids released from sebaceous triglycerides.  Investigation of the toxic Malassezia free fatty acid metabolites (represented by oleic acid) reveals the component of individual susceptibility.

Methods: tFLP (terminal fragment length polymorphism) identifies the presence or absence of fungal species based on polymorphisms in the ITS II region. Quantitative PCR enumerates the number of specific Malassezia species based on variable regions in the ITS I. Scalp sebaceous triglycerides and free fatty acids were determined by swabbing and analysis with gas chromatography. Scalp flaking was assessed by a modified adherent scalp flaking score (Van Abbe, 1964).

Results: We report a tFLP based survey of Malassezia distribution on human scalp revealing the presence of predominantly M. globosa and M. restricta. Malassezia metabolism results in increased levels of scalp free fatty acids. In a randomized, single-site, double blinded clinical study, quantitative PCR shows reduction in both M. restricta and M. globosa, and all other fungi following treatment with ZPT. This results in a decrease in the free fatty acid to triglyceride ratio, resulting in reduced flaking and itch. Application of oleic acid, a predominant sebum component, induces dandruff in susceptible individuals.

Conclusions: Dandruff and seborrheic dermatitis are caused by convergence of at least three etiologic factors: Malassezia restricta and globosa, sebaceous triglycerides, and individual susceptibility. Of these factors, Malassezia are the easiest to control. Pyrithione zinc kills Malassezia and all other fungi, and is highly effective against the Malassezia species actually found on the scalp. Reductions in fungi reduce free fatty acids and thereby scalp flaking and itch.