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 (bacteria, viruses, parasites, 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 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 most 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.