Undecylenic acid has long been understood to be a trusted ingredient in antifungal products. However, its mechanism is more complex than simply killing fungi responsible for infections of the nails. As a result, many companies include undecylenic acid in their products without knowing why. This often leads to poorly developed nail fungus treatments that are ultimately a waste of time and money. This page is dedicated to the discussion of undecylenic acid and its properties that make it an effective antifungal ingredient. We also list the three best undecylenic acid antifungal topical.