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Overview of Fungal Infections

By Sanjay G. Revankar, MD, Professor of Medicine and Director, Infectious Disease Fellowship Program, Division of Infectious Diseases, Wayne State University School of Medicine
Jack D. Sobel, MD, Dean and Distinguished Professor of Medicine, Wayne State University School of Medicine

Fungi are neither plants nor animals. They were once thought to be plants but are now classified as their own kingdom.

  • 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 can grow in two forms:

  • Yeasts: Single round cells

  • Molds: Many cells forming long, thin threads called hyphae

Some fungi go through both forms during their life cycle.

Fungi often grow in soil and decaying plant material. Many fungi, including bread molds and mushrooms, can be seen with the naked eye.

Did You Know...

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

Fungi reproduce by spreading microscopic spores. These spores are often present in the air and soil, 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 types do not cause infection. A few types cause infection only in people who have one of the following:

  • A weakened immune system

  • Foreign material, including medical devices (such as an artificial joint or heart valve), in their body

The immune system may be weakened when people take drugs that suppress the immune system (immunosuppressants), such as chemotherapy drugs or drugs used to prevent rejection of an organ transplant, or have a disorder such as AIDS.

Except for some superficial skin infections, fungal infections are rarely passed from one person to another.

Types of fungal infections

Fungal infections are often described as opportunistic or primary. They can affect many areas of the body (systemic) or only one area (localized).

Opportunistic fungal infections take advantage of a weakened immune system. Thus, they usually occur in people with a weakened immune system, such as those with AIDS. They occur worldwide. Typical opportunistic fungal infections include

Opportunistic fungal infections can be very aggressive, spreading quickly to other organs and often leading to death.

Primary fungal infections can occur in people with a normal immune system, sometimes with serious consequences.

Certain primary fungal infections are more common in certain geographic areas, as in the following examples:

  • Histoplasmosis is especially common in the Ohio and Mississippi River valleys, central New York, and Texas in the United States. It also occurs in parts of Central and South America, Africa, Asia, and Australia.

  • Blastomycosis is particularly common in the eastern and central United States. It also occurs in Africa and in the Saint Lawrence River valley of Canada.

  • Coccidioidomycosis occurs almost exclusively in the Southwest and the central valley of California in the United States and in parts of Mexico and Central and South America.

  • Paracoccidioidomycosis occurs mainly in certain parts South and Central America.

Because many primary fungal infections develop slowly, months or years may pass before people seek medical attention. Typically, if the immune system is normal, fungal infections do not spread to organs deep in the body.

Localized fungal infections affect only one area of the body. They sometimes occur when the normal balances that keep fungi in check are upset. For example, certain types of fungi (such as Candida) are normally present on body surfaces or in the intestine. The bacteria normally present in the digestive tract and vagina limit the growth of these 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.

Localized fungal infections typically involve the skin and nails, vagina, mouth, or sinuses.


  • Antifungal drugs

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

Most fungal infections

Chills, fever, headache, vomiting, a low potassium level* in the blood, kidney failure, and anemia




Aspergillus and candidal infections

Nausea, diarrhea, headache, and rash


Candidal and other fungal infections, including coccidioidomycosis and cryptococcal infections

Nausea, rash, and liver inflammation


Candidal and cryptococcal infections

Nausea, vomiting, and bone marrow damage


Aspergillosis and mucormycosis

Nausea, vomiting, and liver inflammation


Fungal skin infections, histoplasmosis, and other fungal infections

Nausea, diarrhea, liver inflammation, rash, headache, dizziness, a low potassium level* in the blood, high blood pressure, accumulation of fluid (edema), and rarely heart failure


Aspergillus, candidal, and many other fungal infections

Nausea, vomiting, rash, and rarely liver inflammation


Aspergillus and candidal infections, fusariosis, and scedosporiosis

Temporary disturbances in vision (such as blurred vision, changes in color vision, and sensitivity to light) , nausea, vomiting, rash, and liver inflammation

*A low potassium level (hypokalemia) can cause muscle weakness, cramping, and twitches and abnormal heart rhythms.

Flucytosine is usually used with other drugs.

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