Find information on medical topics, symptoms, drugs, procedures, news and more, written in everyday language.

* This is the Consumer Version. *

Overview of Fungal Infections

by Alan M. Sugar, MD

  • Because fungal spores are often present in the air or in the soil, fungal infections usually begin in the lungs or on the skin.

  • Fungal infections are rarely serious unless the immune system is weakened, usually by drugs or disorders.

  • Fungal infections usually progress slowly.

  • Antifungal drugs may be applied directly to the infected site or, if the infection is serious, taken by mouth or injected.

Fungi are neither plants nor animals. They were once thought to be plants but are now classified as their own kingdom. Some fungi, including yeasts such as Candida and molds such as aspergilli, can be seen only through a microscope. Others, including bread molds and mushrooms, can be seen with the naked eye. Fungi can grow in a round shape (as yeasts) or in long, thin threads (hyphae). Some fungi go through both forms during their life cycle.

Some fungi reproduce by spreading microscopic spores. These spores are often present in the air, where they can be inhaled or come into contact with the surfaces of the body, primarily the skin. Consequently, fungal infections usually begin in the lungs or on the skin. Of the wide variety of spores that land on the skin or are inhaled into the lungs, most do not cause infection. Except for some superficial skin infections, fungal infections are rarely passed from one person to another. Typically, if the immune system is normal, fungal infections do not spread to organs deep in the body.

Did You Know...

  • Fungi are their own kingdom—neither plants nor animals.

Certain types of fungi (such as Candida) are normally present on body surfaces or in the intestine. Although normally harmless, these fungi sometimes cause localized infections of the skin and nails (see Fungal Skin Infections), vagina (see Overview of Vaginal Infections), mouth ( Gingivitis Due to Infections), or sinuses (see Fungal Sinus Infections). Fungi seldom cause serious harm, except in people who have a weakened immune system or who have foreign material, including medical devices (such as an intravenous catheter or an artificial joint or heart valve), in their body.

Sometimes the normal balances that keep fungi in check are upset and infections occur. For example, the bacteria normally present in the digestive tract and vagina limit the growth of certain fungi in those areas. When people take antibiotics, the helpful bacteria can be killed, allowing the fungi to grow unchecked. The resulting overgrowth of fungi can cause symptoms, which are usually mild. As the bacteria grow back, the balance is restored, and the problem usually resolves.

Some fungal infections—histoplasmosis, blastomycosis, coccidioidomycosis, and paracoccidioidomycosis—can be serious in otherwise healthy people. The fungi that cause these infections exist in the environment in various parts of the world. Therefore, some fungal infections are more common in certain geographic areas. For example, in the United States, coccidioidomycosis occurs almost exclusively in the Southwest. Histoplasmosis is especially common in the Ohio and Mississippi River valleys. Blastomycosis is particularly common in the eastern and central United States (and in Africa).

Because many fungal infections develop slowly, months or years may pass before people seek medical attention. But in people with a weakened immune system, fungal infections can be very aggressive, spreading quickly to other organs and often leading to death. The immune system may be weakened by taking drugs that suppress the immune system (immunosuppressants), such as chemotherapy drugs or drugs used to prevent rejection of an organ transplant, or by having a disorder, such as AIDS.

Several drugs effective against fungal infections are available, but the structure and chemical makeup of fungi make them difficult to kill. Antifungal drugs may be applied directly to a fungal infection of the skin or other surface, such as the vagina or inside of the mouth. Antifungal drugs may also be taken by mouth or injected when needed to treat more serious infections. For serious infections, several months of treatment are often needed.

Drugs for Serious Fungal Infections


Common Uses

Some Side Effects

Amphotericin B

Wide variety of fungal infections

Chills, fever, headache, vomiting, lowered potassium levels in blood, kidney damage, and anemia




Aspergillus, candidal, and possibly other infections

Fever, nausea, and inflammation of veins


Candidal and other fungal infections, including cryptococcal

Liver inflammation (hepatitis) but less than that with ketoconazole


Candidal and cryptococcal infections

Bone marrow and kidney damage


Candidal and other fungal infections

Nausea, diarrhea, and liver inflammation but less than that with ketoconazole

Erratic absorption of the drug from the intestine


Candidal and other fungal infections

Nausea and vomiting, blocked production of testosterone and cortisol, and liver inflammation


Aspergillus, candidal, and many other fungal infections

Nausea, vomiting, and rarely liver inflammation


Aspergillus and candidal infections

Visual disturbances that are reversible

Resources In This Article

Drugs Mentioned In This Article

  • Generic Name
    Select Brand Names