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What Is an Internal Fungus Infection?

By Don Amerman ; Updated July 27, 2017

Humans share the world with a wide variety of fungi, which are living organisms that can be found in the air, soil, water and plants, as well as on and in the human body. MedlinePlus says that only about half of all known fungi, which are neither plant nor animal in nature, are harmful. When they take up residence in the human body, particularly in those with weakened immune systems, harmful fungi can cause serious infections.

Types of Infection

Fungi can cause four main types of infections, also known as mycoses, according to the website of MicrobiologyBytes. These are superficial, as in skin disorders such as jock itch and athlete’s foot; subcutaneous, confined to the skin and fatty tissue immediately beneath the skin; systemic, involving deep infection of the internal organs; and opportunistic, infections that affect only those with compromised immune systems, as in HIV/AIDS.

How They Spread

Fungi are literally everywhere, and many species of these organisms reproduce through airborne spores, which can land on the body or be inhaled directly into the lungs. If such spores come from harmful types of fungi, they can cause the various types of infections described earlier.

Infection-Causing Fungi

Aspergillus, a genus of fungi or mold, is responsible for the vast majority of internal fungal infections, according to Janssen-Cilag’s Fungal Infections website. Internal infections can begin with the inhalation of spores of a species of Aspergillus fungi. The infection may begin in the lung but can go systemic, particularly in people whose immune systems are weakened, either because of an existing illness or treatment with chemotherapy. Other fungi that can cause internal infections include Candida albicans, Histoplasma capsulatum and Cryptococcus neoformans, according to MicrobiologyBytes.

Fungi-Related Illnesses

The most widely seen internal fungal infections are named for the fungal species that cause them. Simple pulmonary aspergillosis is an allergic reaction to this type of fungus and is usually confined to the lungs, while the invasive type of this infection is much more dangerous and can spread to other parts of the body. Cryptococcosis begins in the lung with the inhalation of fungal spores but can spread to the brain of patients whose immune systems are weakened. Candidiasis may spread from the skin to the esophagus or bloodstream, the latter of which can be a life-threatening development. Histoplasmosis in rare cases can spread throughout much of the system of people with compromised immune systems.


Oral antifungal medications are prescribed for the treatment of internal fungal infections. Antibiotics are not only useless in treating these infections, but they may make patients more vulnerable to fungal infection. Treatment of internal fungal infections is made more problematic by the fact that they target people whose immune systems are least able to fight them off.

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