Many harmful fungus are parasitic on people and have been linked to illnesses in both humans and animals. Parasitic fungus most typically enter the human body through lesions in the epidermis (skin). Insect punctures or inadvertently caused scratches, scrapes, or bruises are examples of such wounds. The fungus then grows within the host's body causing disease. Some fungi cause severe illness or death in humans. These include members of the genera Candida, Aspergillus, and Cryptococcus. Others produce less serious symptoms when they infect humans. For example, histoplasmosis is caused by a fungus named Histoplasma capsulatum that lives in soil contaminated with bird droppings. People become infected when they breathe in the fungus while walking through the forest or other natural areas where it grows. No treatment is available for histoplasmosis; instead, doctors prescribe medications to control the infection or reduce the number of episodes that occur over time. Most fungal infections are treated with drugs called antifungals. There are several classes of antifungal medications, including azoles, polyenes, echinocandins, and amphotericin B. Drugs from all three main classes can be used to treat yeast infections. However, because of the risk of side effects, only one class of drug should be used at a time.