The lipophilic yeast Malassezia furfur belongs to the resident skin flora but has been implicated in various skin diseases. While topical oily preparations may support its growth, their formulation may be altered by yeast-dependent enzymatic degradation. Different synthetic fatty acid (mono-)esters used as refatting agents were mixed with 10(4), 10(5) and 5 x 10(5) yeasts/microliters, respectively, and incubated at 35 degrees C for a maximum of 48 h on selective agar for pathogenic fungi (Merck). The amount and pattern of generated free acids were evaluated by densitometric and gas chromatographic analysis, while yeast density was determined in a Neubauer chamber. Depending on the inoculum, yeast-dependent hydrolysis occurred immediately and was best effected in ethyl esters, followed by isopropyl esters, whereas hydrolysis of decyl oleate was only limited. Of the fatty acids released, unsaturated fatty acids were more stimulative to growth than saturated fatty acids; no toxic effects were observed. In conclusion, yeast-dependent hydrolysis of these synthetic fatty acid (mono-)esters was critically dependent on alcohol moiety, while growth promotion was best effected by unsaturated fatty acids. These results may help to improve the compatibility of topical formulations, especially in seborrheic areas.