Effect of pH on fungal growth: Problems with using vinegar (5% acetic acid) in treating superficial fungal infections

Objectives: To investigate the effect of different pH on the in vitro growth of Trichophyton rubrum (T. rubrum) and to study the pH achievable by a test product at various depths in a porcine nail model. Methods: T. rubrum was grown in Sabouraud dextrose broth of various acidic pH to determine the fungicidal level. A test product with active ingredient of acetic acid was applied to the porcine nails for 60 and 120 times and the pH at various depths of penetration was measured by pH metre. Results: A pH of 3.0 or below is fungicidal to T. rubrum and the minimal pH achievable by 60 and 120 applications of the test product were 4.09 and 3.37 respectively. Conclusions: Use of vinegar (5% acetic acid) to treat tinea pedis is theoretically efficacious but it is difficult to achieve a fungicidal pH of 3.0 at the nail bed despite prolonged application.