The fungi within our bodies may have a much greater effect on our health than we've long given them credit for.

Amongst the millions of tiny life forms living on and inside our bodies are countless species of fungi. Our skin is a mosaic of them, membranes inside the nose and vagina are full of them, and fungi even live alongside the bacteria inside our guts.

While we might acquire some fungi from our mothers at birth, new fungi are also constantly entering our bodies; we ingest yeasts every time we drink beer or eat bread, and we inhale floating fungal spores with every breath. Many of these fungi are quickly killed off by our immune systems, but others are transient passengers or lifelong acquaintances.

Lately, scientists have been exploring how our fungal inhabitants could even influence our brains, minds and behaviour.

Doctors have long known that fungi can cause dangerous brain infections. But researchers are now also finding curious – albeit sometimes controversial – hints that these microbes might have other neurological effects on humans.

The idea might evoke images of the human-zombifying fungus from HBO's apocalyptic series The Last of Us. But while scientists agree that the idea of fungi taking complete control over our bodies is implausible, they're earnestly investigating whether some fungi inside us could contribute to brain-damaging diseases, or if gut-dwelling fungi could influence our behaviour and mental health.

Much more research is needed, experts say. But these possibilities are important to study – both to understand the deep and complex relationships with the microbes within us and to explore new ways of boosting our health.

In general, humans are pretty good at resisting fungi (our warm body temperature tends to make it hard for them to take hold). And many of the fungi that do might actually be good for us, possibly supporting our immune systems or helping wounds to heal, says microbiologist Matthew Olm of the University of Colorado Boulder, US. "I would say fungi are definitely a critical part of being a healthy human," he says.

But many other fungi can cause infections, from athlete's foot to thrush. This happens when we encounter new, harmful fungi in our environment or when fungi that naturally coexist with us are under certain conditions triggered to explode in abundance, says Rebecca Drummond, a fungal immunologist at the University of Birmingham, UK.

It's rare for fungi to reach the brain, thanks to protective barriers in the lungs and intestines, along with the brain's own defensive wall, the blood-brain barrier, and immune cells that are primed to destroy any fungi that slip through. But fungal brain infections do happen, and the number of cases has increased in recent decades.

This is due to a growing number of people with weakened immune systems, Drummond says, partly because of the global spread of the immune-crippling virus HIV, especially in parts of Africa but also due to rising use of immune-suppressing medications in cancer patients and organ transplant........

© BBC