Many types of fungus germs (fungi) live harmlessly in the soil, on food, on our skin, and in other places in the environment. However, some types of fungi can thrive and multiply on the surface of the body to cause infection of the skin, nails, mouth or vagina. These fungal infections are quite common, but are rarely serious and dont usually spread deeper into the body. If you are otherwise healthy and have a normal immune system, it is rare for fungi to affect internal organs. However, fungal infections of the heart, lung, brain, and other organs sometimes do occur. These internal fungal infections can be serious, sometimes life-threatening. Antifungal medicines work by damaging the cell wall of the fungus which causes the fungus cell to die.