Since fungi are eukaryotic, their cellular structure is similar to—if not the same as— that of animals and humans. Drugs that affect fungi often affect corresponding host cells, which can result in the host experiencing drug toxicity. Many antifungal drugs can only be used topically, but very few drugs have been found to be selectively toxic— that is, toxic to fungi and not their human hosts. What scientists try to do to make antifungal drugs work is interfere with the function or synthesis of ergosterol. Ergosterol is found in the cytoplasmic membrane of fungal cells but is not found in human cells. Thus, some antifungal drugs interfere with fungus-specific structures and functions, such as the cell wall.