Fungal Infections

Also known as: Mycoses
Last Review Date: November 27, 2018

What are Fungal Infections?

Fungal infections represent the invasion of tissues by one or more species of fungi. They range from superficial, localised skin conditions to deeper tissue infections to serious lung, blood (septicaemia) or systemic diseases. Some fungi are opportunistic while others are pathogenic, causing disease whether the immune system is healthy or not.

Fungi are one of four major groups of microorganisms (bacteriavirusesparasites, and fungi). They exist in nature in one of two forms: as unicellular yeasts or as branching filamentous moulds. Some fungi are dimorphic - they change from one form to another depending on their environment. While yeasts cannot be seen with the naked eye, moulds can be seen as the fuzzy splotches on overripe fruit or stale bread, as mildew in the bathroom shower, and as mushrooms growing on a rotted log. There are more than 50,000 species of fungi in the environment, but less than 200 species are associated with human disease. Of these, only about 20 to 25 species are common causes of infection.

Most fungal infections occur because a person is exposed to a source of fungi such as spores on surfaces or in the air, soil, or bird droppings. Usually, there is a break or deficiency in the body’s immune system defences and/or the person provides the “right environment” for the fungi to grow. Anyone can have a fungal infection, but certain populations are at an increased risk of fungal infections and recurrence of infections. These include organ transplant recipients, people who have HIV/AIDS, those who are on chemotherapy or immune suppressants, and those who have an underlying condition such as diabetes or lung disease.

Infections involving fungi may occur on the surface of the skin, in skin folds, and in other areas kept warm and moist by clothing and shoes. They may occur at the site of an injury, in mucous membranes, the sinuses, and the lungs. Fungal infections trigger the body’s immune system, can cause inflammation and tissue damage, and in some people may trigger an allergic reaction.

Many infections remain confined to a small area, such as between the toes, but others may spread over the skin and/or penetrate into deeper tissues. Those that progress and those that start in the lungs may move into the blood and be carried throughout the body. Some fungal infections may resolve on their own, but many require medical attention and may need to be treated for extended periods of time. Those that penetrate into the body typically increase in severity over time and, if left untreated, may cause permanent damage and in some cases eventually be fatal. A few fungal infections may be easily passed on to other people, while others typically only affect the infected person.

Fungal infections may be categorized by the part of the body that they affect, by how deeply they penetrate the body, by the organism causing the infection, and by the form(s) that the fungi take. Some organisms may cause both superficial and systemic infections.

Superficial Fungal Infections of Skin, Nail & Hair

Superficial fungal infections may be caused by both yeast and mould forms of fungi. Skin is normally populated with a mixture of microorganisms called normal flora. Most of the time, normal flora do not cause illness and do not stimulate the immune system. If there is a break in the skin or if the immune system becomes compromised, then microorganisms present can cause a wound or skin infection. If there is a shift in the balance of the microorganisms, such as a decrease in bacteria and an increase in the growth of fungi (sometimes seen with the use of broad-spectrum antibiotics), then the person may experience a fungal infection associated with the imbalance.

Yeast infections
Candidiasis, is a common yeast infection that is due primarily to the overgrowth of Candida albicans and other species of Candida, which are part of the normal flora. In the mouth, candidiasis causes redness and white patches and is called “thrush”. In babies, Candida can cause nappy rash. In women, it can cause genital itching and vaginal discharge that is referred to as a “yeast infection.” According to the United States Centers for Disease Control and Prevention (CDC), almost 75% of women will have at least one yeast infection in their lifetime. Candidiasis can also cause a variety of other infections, including nail infections, and can become systemic – especially in those who are immunocompromised. In Australia, while candida infections in the bloodstream are uncommon, 85% of them are associated with hospital admissions.

Fungal (dermatophyte) infections
Athlete’s foot, jock itch, and fungal nail infections are common infections that can be passed from person to person. These fungal infections can cause reddening, peeling, blistering, and scaling of the skin, itching, deformation and brittleness of affected nails, and brittle hair. They are caused by dermatophytes, a group of fungi that includes TrichophytonMicrosporum, and Epidermophyton species. Dermatophytes feed on keratin and rarely penetrate below the skin. Infections caused by these fungi are also commonly called ringworm (although they are not caused by a worm) and “tinea.”

  • Athlete’s foot (tinea pedis) is found between the toes and sometimes covers the bottom of the foot.
  • Jock itch (tinea cruris) may extend from the groin to the inner thigh.
  • Scalp and hair infection (tinea capitis) affects hair shaft, primarily in children.
  • Finger or toenail infection (tinea unguium) typically affects toenails but may also affect fingernails.
  • Ringworm of the body (tinea corporis) can be found anywhere on the body.
  • Barber’s itch (tinea barbae) affects the bearded portion of the face.

Tinea versicolor is associated with multicoloured patches or lesions on the skin and is caused not by a dermatophyte, but by Malassezia furfur, a yeast. It is a condition that is common in young adults. Sporotrichosis is a condition caused by the fungus Sporothrix schenckii, which is not a dermatophyte. It is an infection of the skin and subcutaneous tissue that has been abraded by thorny plants, pine needles, and sphagnum moss where this fungus normally resides.

Deep Tissue, Blood, Lung and Systemic Fungal Infections

A variety of fungi can cause deep and systemic infections. People frequently become infected because they come in contact with the environment where a fungus grows, such as infected soil. Lung infections typically start with the inhalation of fungal spores. With lung infections, and with fungal infections that have spread below the surface of the skin, the invading fungi have the potential to disseminate from the original infection location and move to the blood (septicaemia) and/or spread throughout the body – into organs, tissues, bone, and sometimes into the meninges that cover the spinal cord, and into the brain.

In many patients with competent immune systems, fungal lung infections may cause only mild to moderate flu-like symptoms such as coughing, fever, muscle aches, headaches, and rashes. In other patients, fungi may cause infections that remain localised at the initial site of the infection and do not spread (the organisms are walled off in granulomas). However, people with these localised infections may, at some point in their life, become immunocompromised and the long-standing, silent chronic fungal infection may then become an active acute infection. Some infections caused by fungi may take months to years to cause symptoms, slowly and progressively growing worse and disseminating throughout the body, causing night sweats, chest pain, weight loss, and enlarged lymph nodes. Others may progress rapidly, causing pneumonia and/or septicaemia. Fungal lung infections are more likely to be severe in people who have underlying lung disease and/or compromised immune systems such as those with HIV/AIDS. Both acute and chronic fungal infections can cause permanent lung, organ, and bone damage and can be fatal. Common deep or systemic infections include:

  • Aspergillosis, caused by Aspergillus fumigatus or several other Aspergillus species. These fungi are commonly found in soil, plants, and house dust. They can cause fungal masses in the sinuses and lungs and, in rare cases, can spread to the brain and bones.
  • Candidiasis, caused by Candida species, which are part of the normal human flora, are found worldwide. Infections occur in the moist mucous membranes of the body.
  • Cryptococcosis, caused by Cryptococcus neoformans or Cryptococcus gatti. Cryptococcus can be found in the soil, and C. gatti has been found in association with Eucalyptus trees. Anyone may become infected, but the highest prevalence immunosuppressed people.
  • Pneumocystis pneumonia, caused by Pneumocystis jirovecii (formerly known as Pneumocystis carinii), is found throughout the enviroment worldwide. However, it only causes significant infection in those with compromised immune systems, such as patients with HIV/AIDS or those undergoing chemotherapy or organ transplantation.
  • Histoplasmosis, caused by Histoplasma capsulatum is a rare disease in Australia and most cases have been associated with visiting bat caves. It typically affects the lungs.
  • Blastomycosis, caused by Blastomyces dermatitidis and Coccidiomycosis, caused primarily by Coccidioides immitis cannot be acquired in Australia, but may occur in people who have travelled to regions of North America where these fungi are found.


Laboratory Tests

Various laboratory tests may be used to help diagnose and guide treatment of fungal infections.
For detailed information, see the test article Fungal Tests

Tests for superficial infections
Many fungal skin infections are diagnosed by the doctor based on a clinical evaluation and his or her experience. In addition to general symptoms, many skin infections have characteristic signs, such as the appearance of infected nails and typical locations on the body – such as athlete’s foot between the toes. A clinical evaluation cannot, however, definitively tell the doctor which microorganism is causing a fungal infection. A few laboratory tests may be useful in detecting and confirming a fungal infection and may help guide treatment. They may include:

  • Microscopic examinations, such as potassium hydroxide (KOH) preparation and calcofluor white stain.
  • Fungal culture and susceptibility testing

Tests for deep and systemic infections
With lung and systemic fungal infections, the symptoms are frequently nonspecific and may be confused with those due to other microorganisms or to another disease process. Laboratory testing is primarily used to diagnose these serious fungal infections, to identify the microorganism responsible, and to determine its likely susceptibility to specific antimicrobial agents. Sometimes testing is also performed to detect and identify bacteria that may be causing a concurrent infection. The sample collected depends upon the suspected location(s) of the infection. It may include one or more of the following: the collection of blood, sputum, urine, cerebrospinal fluid (CSF), and/or the collection of a tissue biopsy. Testing may include:

  • Microscopic examination of the sample using techniques such as KOH preparation and calcofluor white stain may be used to quickly determine whether or not the infection is due to a fungus.
  • Fungal culture – This is the primary test used to diagnose a fungal infection. Many fungi are slow-growing and may require up to several weeks for recovery and identification.
  • Susceptibility testing– A follow-up test to the fungal culture that is sometimes ordered to help guide treatment. Susceptibility testing fo most fungi is not available in routine laboratories.
  • Antigen and Antibody testing – Available for a variety of specific fungi but only for deep or systemic infections. May be performed on blood or other body fluids, such as CSF.
  • Molecular tests to detect fungal DNA. These tests can confirm the presence of a fungus and are particularly useful when the fungus culture has not been successful.  Molecular tests are also increasingly used to detect fungi from sterile tissue samples and can be used even after the sample has been preserved with chemicals that prevent the organisms from growing in culture. 

Other tests that may be ordered in conjunction with fungal tests include:

  • Gram stain – a rapid test performed to microscopically detect bacteria and yeasts in a sample.
  • Bacterial culture – used to rule out bacterial infection or determine if a concurrent bacterial infection exists.
  • AFB smear and culture – may be used to rule out tuberculosis or infection due to non-tuberculous mycobacteria.
  • Blood culture – ordered when septicaemia is suspected.
Non-Laboratory Tests

In some cases, imaging scans such as x-rays may be ordered to detect fungal masses, such as in the lungs, and to evaluate the extent of tissue damage.


Some fungal infections are caused by normal flora and by fungi that are present throughout the environment; therefore, not every fungal infection can be prevented and some of them may recur after treatment.

Many superficial fungal infections will resolve with only a topical antifungal treatment, but some cases may require oral antifungal therapy. People with serious lung and systemic fungal infections will require oral and sometimes intravenous medications. The choice of which antifungals to use is based upon the doctor’s experience, on the results of the fungal culture, and on the results of susceptibility testing, if it is available.

Treatment length varies by type, location, and persistence of infection. Vaginal yeast infections, for instance, may require only a few days of therapy to resolve, while fungal skin infections may take a couple of months. Systemic infections may require consistent treatment for a couple of years in order to resolve and, in some cases, people with suppressed immune systems may need to be treated with a maintenance therapy for the rest of their lives. Occasionally, surgery may be necessary to remove fungal masses.


Related Pages

On this site
Tests: Fungal testsAFB smear and cultureCSF analysisSusceptibility testingGram stain
Conditions: Wound and skin infectionsTuberculosis, Lung diseases

Elsewhere on the web
CDC, Division of Bacterial and Mycotic Diseases: Mycotic Disease Listing (USA)
CDC - Fungal Diseases
CDC - Types of fungal diseases
American Society for Microbiology, The Fungal Kingdom: Diverse And Essential Roles In Earth’s Ecosystem

Recent References

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Colonization by Pneumocystis jirovecii and its role in disease. Morris A, Norris KA.
Clin Microbiol Rev. 2012 Apr;25(2):297-317. doi: 10.1128/CMR.00013-12. Review
Molecular and nonmolecular diagnostic methods for invasive fungal infections. Arvanitis M, Anagnostou T, Fuchs BB, Caliendo AM, Mylonakis E. Clin Microbiol Rev. 2014 Jul;27(3):490-526. doi: 10.1128/CMR.00091-13.
Active surveillance for candidemia, Australia. Chen S, Slavin M, Nguyen Q, Marriott D, Playford EG, Ellis D, Sorrell T; Australian Candidemia Study. Emerg Infect Dis. 2006 Oct;12(10):1508-16. PMID: 17176564 [PubMed - indexed for MEDLINE]