Should be applied until healed. However, if after a week there is no improvement then recommend switching to an antibiotic cream. This is usually for those that aren't obviously fungal.If the white areas are "chalky" on touch - this is the fungal infection. Treated with cheap athlete's foot antifungal creme (available in general pharmacies and in some convenience stores without a prescription). Apply daily for a week, gently clean with a soft bristle toothbrush.
To prevent this in future - make sure that top substrate layer is dry (but lower layers should be damp to sustain high humidity).