What is the cause of pityriasis versicolor?
Pityriasis versicolor is caused by yeasts of the genus Malassezia, which may also be found on normal skin. Usually Malassezia species grow sparsely in the seborrhoeic areas (scalp, face and chest) without causing a rash. In some individuals they grow more actively on the skin surface, for unknown reasons. It is easier to demonstrate the yeasts in scrapings taken from the brown type of pityriasis versicolor than from the white type. Microscopy is reported as positive if hyphae and yeast cells are seen; they resemble ‘spaghetti and meatballs’. However, culture is often negative because it is quite difficult to persuade the yeasts to grow in a laboratory. It is only recently that nine different species of Malassezia have been identified. The most common species of yeast cultured from pityriasis versicolor patches are M globosa and M sympodialis. The pale type of pityriasis versicolor is thought to be due to a chemical produced by Malassezia that diffuses down and impairs the function of t
