New strategies in dandruff treatment: growth control of Malassezia ovalis

Background: Cutaneous infections induced by Malassezia ovalis (Pityrosporum ovale) represent a therapeutic problem due to the high rate of recurrence. Objective: We studied feasible strategies to control the growth of M. ovalis, compatible with topical use in cosmetic formulations. Studies were performed on the effects of pH, ionic strength, cinnamic acid and related compounds on mycotic growth. Methods: M. ovalis was cultivated in modified Sabouraud agar. The effects of pH, ionic strength and cinnamic acid and related compounds on mycotic growth were studied by the membrane filter method. Results: In vitro growth of M. ovalisis strongly affected by pH and ionic strength. pH 4.5 induced a growth inhibition of about 95% and 1 M NaCl, at the optimal growth pH, reduced cell growth by over 90%. Cinnamic acid showed an inhibitory effect of 50% at 0.005 g/dl; 30 min incubation with cinnamic acid 0.5 g/dl had a mycocidic effect. Conclusion: These results suggest the use of cosmetic compositions containing cinnamic acid or buffered acidic lotions and shampoos in the treatment of M. ovalis infections of the scalp, eventually in addition or alternative to antimycotic drugs or in maintenance therapy. Cosmetic formulations with high ionic strength or skin irritant derivatives such as cinnamaldehyde cannot be proposed for practical use.