In the middle of an Adelaide day, the bedroom is dark, the curtains closed. Donna Staehr has removed her shirt and stands before me in a maroon singlet. Her skin is flecked with milky dots – scar tissue – and open pink sores. The 44-year-old former nurse assistant ties back her long black hair and picks up a digital microscope plugged into her computer. It looks like a tiny desk lamp and glows white in the dim light. As she puts the microscope to a lesion on her upper breast, it’s like a moment of truth. Will it reveal the strange things she says are inside her?

Staehr says she has Morgellons, a rare disease that mainstream medicine claims is a delusion. Its most famous sufferer, legendary singer Joni Mitchell, 71, described it in 2010 to The Los Angeles Times as a “weird, incurable disease that seems like it’s from outer space”. Mitchell, who collapsed from a brain aneurysm in March, said: “Fibres in a variety of colours protrude out of my skin like mushrooms after a rainstorm: they cannot be forensically identified as animal, vegetable or mineral.”

Fibres in a variety of colours protrude out of my skin like mushrooms after a rainstorm: they cannot be forensically identified as animal, vegetable or mineral.

Staehr moves the microscope from one sore to another, revealing the black, hair-like sticks, like tiny pieces of seaweed, underneath the skin’s surface. Some are white. I put the microscope on a small sore on my arm. No fibres. Perhaps it is from her clothing? “No,” says Staehr, putting the microscope on her shirt. “Clothing fibres look different.” And so it seems.

In 2001, American lab technician Mary Leitao was in her Pennsylvanian home rubbing cream into her toddler’s irritated skin when, she says, a fibre emerged from his skin. Her son, Drew, had been pointing to a sore near his lip and saying “Bugs”. Leitao found more fibres and went from doctor to doctor for help. She had no luck, until one suggested Drew’s problem was not bugs, not fibres, but his mother.

Undeterred, Leitao turned to the internet and blogged about her son’s symptoms. She named his illness from a 1656 letter by the English scholar and author Thomas Browne, in which he writes of a skin condition afflicting French children “called the morgellons, wherein they critically break out with harsh hairs on their backs”. By 2004, she’d set up the Morgellons Research Foundation. Its website united thousands of people all complaining about the same things: lesions, crawling sensations and weird fibres. By 2015, 14,720 families worldwide had registered with the foundation.