Abstract: Objective To investigate the relationship among the pigment change in the skin lesions of pityriasis versicolor, the tryptophan-induced pigment production, and the 7 species of Malassezia. Methods 171 strains of 7 species of Malassezia were isolated from the patients with pityriasis versicolor, and identified by the internationally used biochemical tests. The strains were then cultured on the media with 4 different concentrations of L-tryptophan for 7 days. The degree of pigment production was observed. Results Positive- and negative- pigment-producing strains were observed in all the 7 species. The degree of the pigment production was positively correlated with the concentration of L-tryptophan. The positive-pigment-producing strains were prone to cause the pigmentation in the skin lesion of pityriasis versicolor (P<0.005). Conclusions The pigment production has no relationship with the species of Malassezia. L-Tryptophan is involved in the pigment production of Malassezia.

Key words: Tinea versicolor, Malassezia, Tryptophan