Beyond Spaghetti and Meatballs: Skin Diseases Associated With the Malassezia Yeasts

Introduction

Malassezia are common lipiddependent fungi that grow on the sebaceous areas of human skin, including the face, scalp, and upper trunk. Although Malassezia are a part of the normal human skin flora, they may also cause or exacerbate several skin diseases, including tinea versicolor, Pityrosporum folliculitis, and seborrheic dermatitis. Topical antifungals are the mainstay of treating Malassezia-related diseases. Chronic prophylaxis is often required to prevent recurrences.

Malassezia are lipophilic (lipid-dependent) fungi that compose part of the normal human skin flora, but are now also recognized to play a role in skin disease. Malassezia have clearly been shown to be the causative organism in tinea versicolor and Pityrosporum folliculitis, and are likely to play a role in seborrheic dermatitis (Gupta, Batra, Bluhm, Boekhout, & Dawson, 2004). Evidence for their involvement in other skin conditions, including atopic dermatitis, psoriasis, and neonatal cephalic pustulosis, is weaker.

Malassezia yeasts were first described in the 19th century as budding yeasts found on the skin of patients with dandruff. They are named after Louis-Charles Malassez, a French scientist who identified the yeasts in the outer layer of the epidermis of patients with seborrheic dermatitis. The taxonomy of Mal­assezia has been somewhat confusing, because the genus name Pityro­sporum was historically used for yeast forms whereas the name Malassezia was reserved for hyphal (filamentous) forms, and it was not until molecular methods of species identification became available in the 1980s that Malassezia and Pityro­sporum were found to be identical.

At present, 11 species of Mal­assezia have been identified (Gueho, Midgley, & Guillot, 1996; Sugita et al., 2002; Sugita et al., 2004). The most important clinically are M. globosa, M. sympodialis, M. restricta, M. obtusa, and M. furfur. The different Mal­assezia species are distinguished based on their morphology, growth characteristics, enzyme activities, as well as by molecular methods (Gem­mer, DeAngelis, Theelen, Boekhout, & Dawson, 2002). Malassezia are dimorphic fungi, at times assuming yeast forms and at times hyphal forms, depending on culture conditions. In their yeast form, they may be spherical, oval, or elongated, and they reproduce by unipolar budding. The names Pityrosporum ovale and Pityrosporum orbiculare are still sometimes used when referring to the yeast forms, but it is more correct to refer to both the yeast and hyphal forms using the Malassezia species names.

Dermatology Nursing. 2009;21(1) © 2009 Jannetti Publications, Inc.

Cite this: Beyond Spaghetti and Meatballs: Skin Diseases Associated With the Malassezia Yeasts - Medscape - Jan 01, 2009.