Objective: Seborrhoeic dermatitis is associated with Malassezia furfur, but the exact role of this lipophilic yeast is still unclear. The in vitro antifungal activity of a coal tar gel, the base of the gel and coal tar (Stantar) itself has been evaluated against 54 different M. furfur strains, isolated from patients suffering from dandruff, seborrhoeic dermatitis and pityriasis versicolor.
Methods: Minimum inhibitory concentrations (MICs) of the tested agents were measured by the agar dilution technique.
Results: The coal tar gel was found to be able to inhibit growth of 52 out of 54 investigated M. furfur isolates in vitro at MIC values between 625 and 10,000 micrograms/ml-corresponding to 3-5 micrograms/ml coal tar. However, the gel base also appears to be a less potent inhibitor of in vitro growth of M. furfur. In addition, it could be demonstrated that coal tar alone has an antifungal potential on M. furfur in vitro. MIC values from 250 to 5,000 micrograms/ml for coal tar were found. Presumably, both coal tar as the active ingredient and the gel base contribute to the in vitro activity of the coal tar gel against M. furfur.
Conclusions: It is suggested that the effect of coal tar gel ointment in dandruff and seborrhoeic dermatitis therapy in vivo may be at least partly due to an antifungal activity of the coal tar but also of the gel base.