The role of Malassezia spp in seborrheic dermatitis (SD) is controversial. To compare the cutaneous density and the cultural characteristics of Malassezia in persons with or without SD, quantitative cultures were obtained by stripping the forehead with a tape placed on Leeming and Notman medium. Plates were incubated at 37 degrees C in a plastic bag, and colonies were counted after 14 days. High yeast density was defined as > 100 colony forming units (CFU)/tape. Volunteers were divided into four groups depending on their HIV serology [HIV (+) versus HIV (-) or unknown] and their clinical status (with or without SD). 126/129 cultures were positive (97.7%). Malassezia spp density was low on clinically normal skin in all HIV (-) persons (40/40) but was high in 8/34 (24%) HIV (+) persons without SD (p < 0.001). In SD patients, high densities were found in 10/22 (45%) HIV (+) and in 17/33 (52%) HIV (-) persons. The strains could be divided into three basic groups on the basis of their cultural characteristics. Colony morphology type A predominated on normal skin (72%), and morphology type C predominated on persons with SD (78%). High yeast density can be present without skin symptoms. The pathogenicity of Malassezia seems more likely to be determined by the subtype present on the skin rather than by its density.

The method used is simple, unexpensive and reliable. High Malassezia spp. density was only found in HIV-positive patients.

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