The human body hosts a complex array of microorganisms, collectively known as the microbiome. While much attention often focuses on bacteria, a distinct community of fungi also resides within and on us. This fungal component is known as the mycobiome, an integral, though less explored, part of our overall microbial ecosystem. Understanding this fungal community is important for human health and physiological processes.
Composition of the Human Mycobiome
The mycobiome is distributed across various body sites, each hosting a unique fungal community. In the gastrointestinal tract, fungi typically constitute less than 0.1% of the total microbial community, yet they exhibit high diversity. Common fungal genera found here include Saccharomyces and Candida, with Aspergillus and Penicillium also present.
The skin harbors a more abundant fungal population, sometimes making up to 10% of its microbial inhabitants. On the skin, Malassezia is a predominant fungal genus, identified across many body sites, with high diversity observed in areas like the plantar heel and toenails. The oral cavity also supports a diverse mycobiome, where Candida species are frequently found, alongside Cladosporium, Aspergillus, and Cryptococcus. Fungi also inhabit the respiratory and urogenital tracts.
The Mycobiome’s Role in Bodily Functions
In a healthy state, the mycobiome engages in symbiotic relationships. Fungi within the gut, for instance, interact with the bacterial microbiome, contributing to a balanced microbial environment. These fungi assist in the breakdown of complex carbohydrates and other nutrients that human enzymes cannot fully process, aiding in digestion and nutrient absorption.
Beyond nutrient processing, the mycobiome plays a role in modulating the immune system. A healthy fungal community helps train immune responses, guiding them to differentiate between harmless commensal fungi and potentially harmful pathogens. For example, certain gut fungi, like Candida albicans, can stimulate the activation of specific immune cells, such as Th17 cells, which are involved in protective immune responses. This interaction helps maintain gut homeostasis and immune balance.
Mycobiome Imbalance and Health Conditions
An imbalance in the mycobiome, known as fungal dysbiosis, can contribute to various health conditions. Overgrowth of opportunistic fungi, such as Candida, is a common example. This can lead to localized infections like oral thrush (white patches in the mouth) or vaginal yeast infections (irritation and discharge).
Dysbiosis of the gut mycobiome has been linked to inflammatory bowel disease (IBD), including Crohn’s disease and ulcerative colitis. Patients with IBD often show an altered fungal community, with increased diversity and a higher proportion of fungi like Candida and Malassezia. For instance, Malassezia species have been associated with Crohn’s disease, particularly in individuals with certain genetic predispositions. On the skin, Malassezia species are also implicated in conditions such as dandruff and certain forms of eczema, where their overgrowth can trigger inflammatory responses.
Factors That Influence Your Mycobiome
Mycobiome composition is shaped by internal and external factors. Diet plays a role, as food choices directly influence gut fungal communities. Diets rich in simple sugars can promote the growth of certain yeasts like Candida, potentially leading to overgrowth. Conversely, a diet rich in fiber can support a more diverse and balanced fungal community.
Medications, particularly antibiotics, can impact the mycobiome. By reducing bacterial populations, antibiotics can allow fungi, such as Candida albicans, to overgrow due to reduced competition. Antifungal medications also directly alter fungal populations, often targeting specific species.
Host-specific factors, including genetics, also contribute to mycobiome variations. For example, certain genetic variations, such as in the CARD9 gene, have been associated with the presence of Malassezia in the gut. Immune system strength, age, and biological sex can also influence fungal colonization patterns. Environmental factors like geographical location and lifestyle practices also introduce diverse fungal species to the body.