The nature extinction crisis is mirrored by one in our own bodies. Both have huge implications for health

The outdoors is good for us, and the greater the richness of species we’re among, the more healthy microbes make their way to our bodies. Photograph: Ruben Earth/Getty Images

Human bodies are like cities, teeming with microcitizens – vast communities of viruses, fungi and bacteria that live all over our skin and inside us. Unsung public servants help us digest food, regulate our immune system, defend against pathogens, and keep hormones in check. Together, they make up what we call the human microbiome.

Most people have probably heard of the gut microbiome, but different microbes thrive all over our bodies – in our nostrils, on our feet, in our eyes. They are slightly different, like boroughs are composed of different communities of people. Ninety per cent of cells in our body are microbes, and “clouds” of bacteria come off someone’s body as they enter a room. We are all walking ecosystems, picking up and shedding material as we move through life.